COMPARTMENTS Text-mining Protein Localization Evidence Scores Dataset

Description gene-cellular compartment co-occurrence scores from text-mining biomedical abstracts
Measurement association by text-mining
Association protein-cellular component associations from automated text-mining of biomedical literature
Category structural or functional annotations
Resource COMPARTMENTS
Citation(s)
Last Updated
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  1. 14375 genes
  2. 2081 cellular components
  3. 546634 gene-cellular component associations

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cellular component Gene Sets

2081 sets of proteins co-occuring with cellular components in abstracts of biomedical publications from the COMPARTMENTS Text-mining Protein Localization Evidence Scores dataset.

Gene Set Description
1,3-beta-d-glucan synthase complex A protein complex that catalyzes the transfer of a glucose group from UDP-glucose to a (1->3)-beta-D-glucan chain.
3-methyl-2-oxobutanoate dehydrogenase (lipoamide) complex A protein complex that catalyzes the reaction 3-methyl-2-oxobutanoate + lipoamide = S-(2-methylpropanoyl)-dihydrolipoamide + carbon dioxide (CO2). This requires thiamine diphosphate; the enzyme also acts on (S)-3-methyl-2-oxopentanoate and 4-methyl-2-oxo-pentanoate.
3-methylcrotonyl-coa carboxylase complex, mitochondrial A heterodimeric complex having 3-methylcrotonyl-CoA carboxylase activity. The alpha subunit has a covalently bound biotin essential for the ATP-dependent carboxylation. The beta subunit possess carboxyltransferase activity which presumably is essential for binding to 3-methylcrotonyl-CoA.
3-phenylpropionate dioxygenase complex Enzyme complex consisting of four proteins: the two subunits of the hydroxylase component (hcaE and hcaF), a ferredoxin (hcaC) and a ferredoxin reductase (hcaD). Converts 3-phenylpropionic acid (PP) into cis-3-(3-carboxyethyl)-3,5-cyclohexadiene-1,2-diol (PP-dihydrodiol).
4-aminobutyrate transaminase complex A homodimeric protein complex that possesses 4-aminobutyrate transaminase activity.
90s preribosome A large ribonucleoprotein complex considered to be the earliest preribosomal complex. In S. cerevisiae, it has a size of 90S and consists of the 35S pre-rRNA, early-associating ribosomal proteins most of which are part of the small ribosomal subunit, the U3 snoRNA and associated proteins.
a band The dark-staining region of a sarcomere, in which myosin thick filaments are present; the center is traversed by the paler H zone, which in turn contains the M line.
acetyl-coa carboxylase complex A protein complex that catalyzes the first step in long-chain fatty acid biosynthesis. For example, in E. coli the complex is heterohexameric and composed of biotin carbonyl carrier protein, biotin carboxylase and the acetate CoA-transferase complex.
acetyl-coa decarbonylase/synthase-carbon monoxide dehydrogenase complex A multifunctional enzyme complex composed of five different polypeptides that catalyzes the decarbonylation of acetyl-CoA, cleaves the C-C and C-S bonds in the acetyl moiety of acetyl-CoA, oxidizes the carbonyl group to CO2 and transfers the methyl group to tetrahydrosarcinapterin. These reactions are important for methanogenesis.
acetylcholine-gated channel complex A homo- or hetero-pentameric protein complex that forms a transmembrane channel through which ions may pass in response to acetylcholine binding.
acetyltransferase complex A protein complex which is capable of acetyltransferase activity.
acf complex An ISWI complex that contains an ATPase subunit of the ISWI family (SNF2H in mammals, Isw2 in S. cerevisiae), an ACF1 homolog, and generally no other subunits, though Xenopus is an exception with a third non-conserved subunit. ACF plays roles in regulation of RNA polymerase II transcription and in DNA replication and repair.
acidocalcisome An electron-dense acidic membrane-bounded organelle which contains a matrix of pyrophosphate and polyphosphates with bound calcium and other cations.
acidocalcisome membrane The lipid bilayer surrounding an acidocalcisome.
acroblast A cone-shaped structure in the head of a spermatozoon, which is formed by the coalescence of Golgi fragments following the completion of meiosis. The acroblast is situated adjacent to the acrosomal vesicle.
acrosomal lumen The volume enclosed within the acrosome membrane.
acrosomal matrix A structural framework, or 'dense core' at the interior of an acrosome. May regulate the distribution of hydrolases within the acrosome and their release during the acrosome reaction.
acrosomal membrane The membrane that surrounds the acrosomal lumen. The acrosome is a special type of lysosome in the head of a spermatozoon that contains acid hydrolases and is concerned with the breakdown of the outer membrane of the ovum during fertilization.
acrosomal vesicle A structure in the head of a spermatozoon that contains acid hydrolases, and is concerned with the breakdown of the outer membrane of the ovum during fertilization. It lies just beneath the plasma membrane and is derived from the lysosome.
actin cap Polarized accumulation of cytoskeletal proteins (including F-actin) and regulatory proteins in a cell. An example of this is the actin cap found in Saccharomyces cerevisiae.
actin cortical patch An endocytic patch that consists of an actin-containing structure found at the plasma membrane in cells; formed of networks of branched actin filaments that lie just beneath the plasma membrane and assemble, move, and disassemble rapidly. An example of this is the actin cortical patch found in Saccharomyces cerevisiae.
actin cytoskeleton The part of the cytoskeleton (the internal framework of a cell) composed of actin and associated proteins. Includes actin cytoskeleton-associated complexes.
actin filament A filamentous structure formed of a two-stranded helical polymer of the protein actin and associated proteins. Actin filaments are a major component of the contractile apparatus of skeletal muscle and the microfilaments of the cytoskeleton of eukaryotic cells. The filaments, comprising polymerized globular actin molecules, appear as flexible structures with a diameter of 5-9 nm. They are organized into a variety of linear bundles, two-dimensional networks, and three dimensional gels. In the cytoskeleton they are most highly concentrated in the cortex of the cell just beneath the plasma membrane.
actin filament bundle An assembly of actin filaments that are on the same axis but may be oriented with the same or opposite polarities and may be packed with different levels of tightness.
actin rod A cellular structure consisting of parallel, hexagonally arranged actin tubules, comprising filamentous actin and associated proteins. Found in the germinating spores of Dictyostelium discoideum.
activin a complex A nonsteroidal regulator, composed of two covalently linked inhibin beta-A subunits (sometimes known as activin beta-A or activin/inhibin beta-A).
activin ab complex A nonsteroidal regulator, composed of two covalently linked inhibin beta subunits (sometimes known as activin beta or activin/inhibin beta), inhibin beta-A and inhibin beta-B.
activin complex A nonsteroidal regulator, composed of two covalently linked inhibin beta subunits, inhibin beta-A and inhibin beta-B (sometimes known as activin beta or activin/inhibin beta). There are three forms of activin complex, activin A, which is composed of 2 inhibin beta-A subunits, activin B, which is composed of 2 inhibin beta-B subunits, and activin AB, which is composed of an inhibin beta-A and an inhibin beta-B subunit.
activin receptor complex A protein complex that acts as an activin receptor. Heterodimeric activin receptors, comprising one Type I activin receptor and one Type II receptor polypeptide, and heterotrimeric receptors have been observed.
actomyosin Any complex of actin, myosin, and accessory proteins.
actomyosin contractile ring A cytoskeletal structure composed of actin filaments and myosin that forms beneath the plasma membrane of many cells, including animal cells and yeast cells, in a plane perpendicular to the axis of the spindle, i.e. the cell division plane. Ring contraction is associated with centripetal growth of the membrane that divides the cytoplasm of the two daughter cells. In animal cells, the contractile ring is located inside the plasma membrane at the location of the cleavage furrow. In budding fungal cells, e.g. mitotic S. cerevisiae cells, the contractile ring forms beneath the plasma membrane at the mother-bud neck before mitosis.
ada2/gcn5/ada3 transcription activator complex A multiprotein complex that possesses histone acetyltransferase and is involved in regulation of transcription. Contains either GCN5 or PCAF in a mutually exclusive manner. The budding yeast complex includes Gcn5p, two proteins of the Ada family, and two TBP-associate proteins (TAFs); analogous complexes in other species have analogous compositions, and usually contain homologs of the yeast proteins. Both ATAC- or SAGA (see GO:0000124, SAGA complex) are involved in the acetylation of histone H3K9 and K14 residues.
adherens junction A cell junction at which anchoring proteins (cadherins or integrins) extend through the plasma membrane and are attached to actin filaments.
aggresome An inclusion body formed by dynein-dependent retrograde transport of an aggregated protein on microtubules.
aim2 inflammasome complex A protein complex that consists of AIM2, ASC, and caspase-1. AIM2 is a member of the HN-200 protein family that appears to be the sensor of cytosolic double-stranded DNA.
aleurone grain A membrane-bounded storage granule found in cells of the aleurone layer in plants; contains either a protein matrix, protein-carbohydrate bodies and/or globoids. Aleurone grains are formed by the vacuole, rough endoplasmic reticulum and dictyosomes.
aleurone grain membrane The lipid bilayer surrounding an aleurone grain.
alpha dna polymerase:primase complex A complex of four polypeptides, comprising large and small DNA polymerase alpha subunits and two primase subunits, which catalyzes the synthesis of an RNA primer on the lagging strand of replicating DNA; the smaller of the two primase subunits alone can catalyze oligoribonucleotide synthesis.
alpha,alpha-trehalose-phosphate synthase complex (udp-forming) A protein complex that possesses alpha,alpha-trehalose-phosphate synthase (UDP-forming) and trehalose-phosphatase activities, and thus catalyzes two reactions in trehalose biosynthesis. In the complex identified in Saccharomyces, Tps1p has alpha,alpha-trehalose-phosphate synthase (UDP-forming) activity, Tps2p has trehalose 6-phosphate phosphatase activity; Tps3p is a regulatory subunit, and an additional subunit, Tsl1p, may be present.
alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid selective glutamate receptor complex An assembly of four or five subunits which form a structure with an extracellular N-terminus and a large loop that together form the ligand binding domain. The C-terminus is intracellular. The ionotropic glutamate receptor complex itself acts as a ligand gated ion channel; on binding glutamate, charged ions pass through a channel in the center of the receptor complex. The AMPA receptors mediate fast synaptic transmission in the CNS and are composed of subunits GluR1-4, products from separate genes. These subunits have an extracellular N-terminus and an intracellular C-terminus.
alpha-beta t cell receptor complex A T cell receptor complex in which the TCR heterodimer comprises alpha and beta chains, associated with the CD3 complex; recognizes a complex consisting of an antigen-derived peptide bound to a class I or class II MHC protein.
alpha3-beta1 integrin-cd151 complex A protein complex that consists of an alpha3-beta1 integrin complex bound to the tetraspanin CD151.
alphaiib-beta3 integrin-cd9 complex A protein complex that consists of an alphaIIb-beta3 integrin complex bound to the cell surface protein CD9.
alphav-beta3 integrin-egfr complex A protein complex that consists of an alphaV-beta3 integrin complex bound to epidermal growth factor receptor.
alphav-beta3 integrin-vitronectin complex A protein complex that consists of an alphav-beta3 integrin complex bound to vitronectin.
aminoacyl-trna synthetase multienzyme complex A multienzyme complex found in all multicellular eukaryotes composed of eight proteins with aminoacyl-tRNA synthetase activities (abbreviated as: ArgRS, AspRS, GluProRS, GlnRS, IleRS, LeuRS, LysRS, MetRS where RS is the enzyme, preceded by the amino acid it uses as a substrate) as well as three non-synthetase proteins (p43, p38, and p18) with diverse functions. Several of these subunits are known dimers, so the total polypeptide count in the multisynthetase complex is at least fifteen. All of the enzymes in this assembly catalyze the same reaction, the covalent attachment of an amino acid to either the 2'- or 3'-hydroxyl of the 3'-terminal adenosine of tRNA, but using different substrates.
amorphous vesicle A cytoplasmic membrane-bounded vesicle first described in dendrites, categorized by smooth membranes, electron-lucent interiors and irregular shapes. Sometimes occurs in clumps. Amorphous vesicles have been found to contain material taken up from the extracellular space, therefore suggesting that they may be part of the endosomal pathway.
amp-activated protein kinase complex A protein complex that possesses AMP-dependent protein kinase activity.
amphisome An autophagic vacuole formed upon fusion between autophagosomes and endosomes.
amyloplast A plastid whose main function is to synthesize and store starch.
amyloplast envelope The double lipid bilayer enclosing the amyloplast and separating its contents from the rest of the cytoplasm; includes the intermembrane space.
amyloplast membrane Either of the lipid bilayers that surround an amyloplast and form the amyloplast envelope.
anammoxosome An intracytoplasmic membrane-bounded compartment in anaerobic ammonium oxidation (anammox) bacteria, is the site of anammox catabolism.
anaphase-promoting complex A ubiquitin ligase complex that degrades mitotic cyclins and anaphase inhibitory protein, thereby triggering sister chromatid separation and exit from mitosis. Substrate recognition by APC occurs through degradation signals, the most common of which is termed the Dbox degradation motif, originally discovered in cyclin B.
anchored component of membrane The component of a membrane consisting of the gene products that are tethered to the membrane only by a covalently attached anchor, such as a lipid group that is embedded in the membrane. Gene products with peptide sequences that are embedded in the membrane are excluded from this grouping.
anchored component of plasma membrane The component of the plasma membrane consisting of the gene products that are tethered to the membrane only by a covalently attached anchor, such as a lipid group, that is embedded in the membrane. Gene products with peptide sequences that are embedded in the membrane are excluded from this grouping.
anchoring collagen complex Any collagen complex which links one collagen assembly, such as a collagen fibril or sheet, to other structures.
anchoring junction A cell junction that mechanically attaches a cell (and its cytoskeleton) to neighboring cells or to the extracellular matrix.
angiogenin-pri complex A stable heterodimer of angiogenin and placental ribonuclease inhibitor; interaction between angiogenin and PRI prevents angiogenin binding to its receptor to stimulate angiogenesis.
annulate lamellae Stacks of endoplasmic reticulum (ER) membranes containing a high density of nuclear pores, thought to form from excess nuclear membrane components, that have been described in a number of different cells. Annulate lamellar membranes are continuous with and embedded within the ER.
annuli extracellular matrix The extracellular matrix that is a regularly spaced circumferential ridge present in the cortical region of the cuticle. Annuli are delineated by annular furrows and are present throughout the cuticle with the exception of lateral regions where longitudinal alae are present.
anthranilate synthase complex A heterotetrameric enzyme complex made up of two components I and two components II. Catalyzes the formation of anthranilate, pyruvate and L-glutamate from chorismate and L-glutamine.
ap-1 adaptor complex A heterotetrameric AP-type membrane coat adaptor complex that consists of beta1, gamma, mu1 and sigma1 subunits and links clathrin to the membrane surface of a vesicle; vesicles with AP-1-containing coats are normally found primarily in the trans-Golgi network. In at least humans, the AP-1 complex can be heterogeneric due to the existence of multiple subunit isoforms encoded by different genes (gamma1 and gamma2, mu1A and mu1B, and sigma1A, sigma1B and sigma1C).
ap-2 adaptor complex A heterotetrameric AP-type membrane coat adaptor complex that consists of alpha, beta2, mu2 and sigma2 subunits, and links clathrin to the membrane surface of a vesicle; vesicles with AP-2-containing coats are normally found primarily near the plasma membrane, on endocytic vesicles. In at least humans, the AP-2 complex can be heterogeneric due to the existence of multiple subunit isoforms encoded by different alpha genes (alphaA and alphaC).
ap-3 adaptor complex A heterotetrameric AP-type membrane coat adaptor complex that consists of beta3, delta, mu3 and sigma3 subunits and is found associated with endosomal membranes. AP-3 does not appear to associate with clathrin in all organisms. In at least humans, the AP-3 complex can be heterogeneric due to the existence of multiple subunit isoforms encoded by different genes (beta3A and beta3B, mu3A and mu3B, and sigma3A and sigma3B).
ap-type membrane coat adaptor complex Any of several heterotetrameric complexes that link clathrin (or another coat-forming molecule, as hypothesized for AP-3 and AP-4) to a membrane surface; they are found on coated pits and coated vesicles, and mediate sorting of cargo proteins into vesicles. Each AP complex contains two large (a beta and one of either an alpha, gamma, delta, or epsilon) subunits (110-130 kDa), a medium (mu) subunit (approximately 50 kDa), and a small (sigma) subunit (15-20 kDa).
apc-tubulin-iqgap1 complex A protein complex that contains the tumor suppressor protein adenomatous polyposis coli (APC), alpha-tubulin, gamma-tubulin, and the Rac1 and Cdc42 effector IQGAP1; may play a role in cytoskeleton organization.
apical complex A group of cytoskeletal structures and associated membrane-bounded organelles found at the anterior end of adult obligate intracellular protozoan parasites in the phylum Apicomplexa. The apical complex is involved in attachment to and penetration of the host cell, and in parasite proliferation.
apical cortex The region that lies just beneath the plasma membrane on the apical edge of a cell.
apical dendrite A dendrite that emerges near the apical pole of a neuron. In bipolar neurons, apical dendrites are located on the opposite side of the soma from the axon.
apical junction complex A functional unit located near the cell apex at the points of contact between epithelial cells, which in vertebrates is composed of the tight junction, the zonula adherens, and desmosomes and in some invertebrates, such as Drosophila, is composed of the subapical complex (SAC), the zonula adherens and the septate junction. Functions in the regulation of cell polarity, tissue integrity and intercellular adhesion and permeability.
apical lamina of hyaline layer A fibrous network that is part of the hyalin layer extracellular matrix. The apical lamina is thought to be principally composed of the glycoproteins fibropellins. This matrix has been found in echinoderms.
apical part of cell The region of a polarized cell that forms a tip or is distal to a base. For example, in a polarized epithelial cell, the apical region has an exposed surface and lies opposite to the basal lamina that separates the epithelium from other tissue.
apical plasma membrane The region of the plasma membrane located at the apical end of the cell.
apicolateral plasma membrane The apical end of the lateral plasma membrane of epithelial cells.
apicoplast The plastid organelle found in apicomplexans.
apolipoprotein b mrna editing enzyme complex Protein complex that mediates editing of the mRNA encoding apolipoprotein B; catalyzes the deamination of C to U (residue 6666 in the human mRNA). Contains a catalytic subunit, APOBEC-1, and other proteins (e.g. human ASP; rat ASP and KSRP).
apoplast The cell membranes and intracellular regions in a plant are connected through plasmodesmata, and plants may be described as having two major compartments: the living symplast and the non-living apoplast. The apoplast is external to the plasma membrane and includes cell walls, intercellular spaces and the lumen of dead structures such as xylem vessels. Water and solutes pass freely through it.
apoptosome A multisubunit protein complex involved in the signaling phase of the apoptotic process. In mammals it is typically composed of seven Apaf-1 subunits bound to cytochrome c and caspase-9. A similar complex to promote apoptosis is formed from homologous gene products in other eukaryotic organisms.
apoptotic body A fragment containing parts of a dying cell. Apoptotic bodies can be formed during the execution phase of the apoptotic process, when the cell's cytoskeleton breaks up and causes the membrane to bulge outward. These bulges may separate from the cell, taking a portion of cytoplasm with them, to become apoptotic bodies. These are then engulfed by phagocytic cells, and their components recycled.
arbuscule Highly branched symbiont haustoria within host root cortex cells, responsible for nutrient exchange.
arc complex A ribonucleoprotein complex that contains members of the Argonaute family of proteins, additional protein subunits, and duplex siRNA; required for heterochromatin assembly and siRNA generation. Possibly involved in the conversion of ds siRNA to ss siRNA.
arp2/3 protein complex A stable protein complex that contains two actin-related proteins, Arp2 and Arp3, and five novel proteins (ARPC1-5), and functions in the nucleation of branched actin filaments.
aryl hydrocarbon receptor complex A protein complex that acts as an aryl hydrocarbon (Ah) receptor. Cytosolic and nuclear Ah receptor complexes have different subunit composition, but both contain the ligand-binding subunit AhR.
ascospore wall The specialized cell wall of the ascospore (spore), which is the product of meiotic division. Examples of this component are found in Fungi.
ascospore-type prospore An immature spore undergoing development. The spore usually consists of nucleic acid, prospore membrane(s) that encase the nucleic acid, and ultimately a cell wall that covers the membrane(s). This type of spore is observed in ascospore-forming fungi.
ascus epiplasm Ascus cytoplasm that is not packaged into ascospores.
assemblon Antigenically dense structures located at the periphery of nuclei, close to but not abutting nuclear membranes. Assemblons contain the proteins for immature-capsid assembly; they are located at the periphery of a diffuse structure composed of proteins involved in DNA synthesis, which overlaps only minimally with the assemblons. More than one site can be present simultaneously.
aster An array of microtubules emanating from a spindle pole MTOC that do not connect to kinetochores.
astra complex A protein complex that is part of the chromatin remodeling machinery; the acronym stands for ASsembly of Tel, Rvb and Atm-like kinase. In Saccharomyces cerevisiae this complex includes Rvb1p, Rvb2p, Tra1p, Tel2p, Asa1p, Ttilp and Tti2p.
astral microtubule Any of the spindle microtubules that radiate in all directions from the spindle poles and are thought to contribute to the forces that separate the poles and position them in relation to the rest of the cell.
astrocyte end-foot Terminal process of astrocyte abutting non-neuronal surfaces in the brain.
astrocyte projection A prolongation or process extending from the soma of an astrocyte and wrapping around neurons.
asymmetric synapse A type of synapse occurring between an axon and a dendritic spine or dendritic shaft. Asymmetric synapses, the most abundant synapse type in the central nervous system, involve axons that contain predominantly spherical vesicles and contain a thickened postsynaptic density.
atg12-atg5-atg16 complex A protein complex required for the expansion of the autophagosomal membrane. In budding yeast, this complex consists of Atg12p, Atg5p and Atg16p.
atp-binding cassette (abc) transporter complex A complex for the transport of metabolites into and out of the cell, typically comprised of four domains; two membrane-associated domains and two ATP-binding domains at the intracellular face of the membrane, that form a central pore through the plasma membrane. Each of the four core domains may be encoded as a separate polypeptide or the domains can be fused in any one of a number of ways into multidomain polypeptides. In Bacteria and Archaebacteria, ABC transporters also include substrate binding proteins to bind substrate external to the cytoplasm and deliver it to the transporter.
atp-binding cassette (abc) transporter complex, transmembrane substrate-binding subunit-containing A complex for the transport of metabolites into the cell, consisting of 4 subunits: a transmembrane substrate-binding protein (known as the S component), and an energy-coupling module that comprises two ATP-binding proteins (known as the A and A' components) and a transmembrane protein (known as the T component). Transport of the substrate across the membrane is driven by the hydrolysis of ATP.
atp-sensitive potassium channel complex A protein complex that comprises four pore-forming (Kir6.x) and four regulatory sulphonylurea receptor (SURx) subunits and forms a transmembrane channel through which ions may pass. The opening and closing of the channel is regulated by ATP: binding of ATP to the Kir6.2 subunit inhibits channel activity, whereas binding of Mg2+-complexed ATP or ADP to the SUR1 subunit stimulates channel activity.
atpase dependent transmembrane transport complex A transmembrane protein complex that functions in ATPase dependent active transport across a membrane.
atr-atrip complex A protein complex that contains the protein kinase ATR and ATR-interacting protein (ATRIP) and binds single-stranded DNA; ssDNA binding affinity is increased in the presence of replication protein A.
attachment organelle A membrane-bounded extension of the cell, originally characterized in Mycoplasma species, that contains an electron-dense core that is part of the cytoskeleton and is oriented lengthwise and ends distally in a bulbous knob (terminal button). Required for adherence to host cells and involved in gliding motility and cell division.
autolysosome A type of secondary lysosome in which a primary lysosome has fused with the outer membrane of an autophagosome. It is involved in the second step of autophagy in which it degrades contents with acidic lysosomal hydrolases.
autophagic vacuole A double-membrane-bounded compartment in which endogenous cellular material is sequestered; known as autophagosome in yeast.
autophagic vacuole membrane The lipid bilayer surrounding an autophagic vacuole, a double-membrane-bounded vesicle in which endogenous cellular material is sequestered.
autosome Any chromosome other than a sex chromosome.
axolemma The portion of the plasma membrane surrounding an axon; it is a specialized trilaminar random mosaic of protein molecules floating within a fluid matrix of highly mobile phospholipid molecules, 7-8 nm in thickness.
axon The long process of a neuron that conducts nerve impulses, usually away from the cell body to the terminals and varicosities, which are sites of storage and release of neurotransmitter.
axon collateral Any of the smaller branches of an axon that emanate from the main axon cylinder.
axon hillock Portion of the neuronal cell soma from which the axon originates.
axon initial segment Portion of the axon proximal to the neuronal cell body, at the level of the axon hillock. The action potentials that propagate along the axon are generated at the level of this initial segment.
axon part A part of an axon, a cell projection of a neuron.
axon terminus Terminal inflated portion of the axon, containing the specialized apparatus necessary to release neurotransmitters. The axon terminus is considered to be the whole region of thickening and the terminal button is a specialized region of it.
axonal growth cone The migrating motile tip of a growing nerve cell axon.
axonal spine A spine that originates from the axon, usually from the initial segment.
axonemal dynein complex A dynein complex found in eukaryotic cilia and flagella; the motor domain heads interact with adjacent microtubules to generate a sliding force which is converted to a bending motion. May contain two or three dynein heavy chains as well as several light chains.
axonemal microtubule A microtubule in the axoneme of a eukaryotic cilium or flagellum; an axoneme contains nine modified doublet microtubules, which may or may not surround a pair of single microtubules.
axoneme The bundle of microtubules and associated proteins that forms the core of cilia (also called flagella) in eukaryotic cells and is responsible for their movements.
axoneme part Any constituent part of an axoneme, the bundle of microtubules and associated proteins that forms the core of cilia (also called flagella) in eukaryotic cells and is responsible for their movements.
azurophil granule Primary lysosomal granule found in neutrophil granulocytes. Contains a wide range of hydrolytic enzymes and is released into the extracellular fluid.
azurophil granule membrane The lipid bilayer surrounding an azurophil granule, a primary lysosomal granule found in neutrophil granulocytes that contains a wide range of hydrolytic enzymes and is released into the extracellular fluid.
b cell receptor complex An immunoglobulin complex that is present in the plasma membrane of B cells and that in its canonical form is composed of two identical immunoglobulin heavy chains and two identical immunoglobulin light chains and a signaling subunit, a heterodimer of the Ig-alpha and Ig-beta proteins.
b800-850 antenna complex Protein-pigment complex that absorbs light at 800 and 850 nm; is peripherally associated to the bacterial reaction center; transfers excitation energy to the B875 antenna complex.
b875 antenna complex Protein complex that surrounds and transfers excitation energy directly to the bacterial reaction center; binds bacteriochlorophyll a and has a single absorption band between 870 and 890 nm.
bacterial nucleoid The region of a bacterial cell to which the DNA is confined.
bacterial-type flagellum A motor complex composed of an extracellular helical protein filament coupled to a rotary motor embedded in the cell envelope.
bacterial-type flagellum basal body One of the three major substructures of the flagellin-based flagellum; a structure consisting of a rod, a series of rings, the Mot proteins, the switch complex and the flagellum-specific export apparatus. The rings anchor the flagellum to the cytoplasmic membrane (MS ring), the peptidoglycan (P ring) and the outer membrane (L ring). Examples of this component are found in bacteria.
bacterial-type flagellum filament The long (approximately 20 nm), thin external structure of the flagellum, which acts as a propeller. Examples of this component are found in bacteria.
bacterial-type flagellum hook The portion of the flagellum that connects the filament to the basal body. Examples of this component are found in bacteria.
bacterial-type flagellum part Any constituent part of flagellum, a 20 nm diameter filament composed of subunits of flagellin driven passively at its base by a motor powered by the transmembrane proton potential. Examples of this component are found in bacterial species.
bacteroid-containing symbiosome A symbiosome containing any of various structurally modified bacteria, such as those occurring on the root nodules of leguminous plants.
bad-bcl-2 complex A heterodimeric protein complex consisting of BAD and BCL-2, members of the Bcl-2 family of anti- and proapoptotic regulators.
bad-bcl-xl complex A heterodimeric protein complex consisting of BAD and BCL-xl, members of the Bcl-2 family of anti- and proapoptotic regulators.
baf-type complex A SWI/SNF-type complex that contains a subunit from the BAF (Brahma-Associated Factor) family.
bak complex An oligomeric protein complex consisting of BAK, a member of the Bcl-2 family of anti- and proapoptotic regulators.
barr body A structure found in a female mammalian cell containing an unpaired X chromosome that has become densely heterochromatic, silenced and localized at the nuclear periphery.
barrier septum A septum which spans a cell and does not allow exchange of organelles or cytoplasm between compartments.
basal cortex The region that lies just beneath the plasma membrane on the basal edge of a cell.
basal labyrinth A region in the lower half of some cells formed from extensive infoldings of the basal plasma membrane; includes cytoplasm adjacent to the infolded membrane.
basal lamina A thin sheet of proteoglycans and glycoproteins, especially laminin, secreted by cells as an extracellular matrix.
basal part of cell The region of a cell situated near the base. For example, in a polarized epithelial cell, the basal surface rests on the basal lamina that separates the epithelium from other tissue.
basal plasma membrane The region of the plasma membrane located at the basal end of the cell. Often used in reference to animal polarized epithelial membranes, where the basal membrane is the part attached to the extracellular matrix, or in plant cells, where the basal membrane is defined with respect to the zygotic axis.
basal pole of neuron Portion of a neuron cell soma closest to the point where the basilar dendrite emerges.
basement membrane A thin layer of dense material found in various animal tissues interposed between the cells and the adjacent connective tissue. It consists of the basal lamina plus an associated layer of reticulin fibers.
basement membrane collagen trimer Any collagen timer that is part of a basement membrane.
basilar dendrite A dendrite that emerges near the basal pole of a neuron. In bipolar neurons, basal dendrites are either on the same side of the soma as the axon, or project toward the axon.
basolateral plasma membrane The region of the plasma membrane that includes the basal end and sides of the cell. Often used in reference to animal polarized epithelial membranes, where the basal membrane is the part attached to the extracellular matrix, or in plant cells, where the basal membrane is defined with respect to the zygotic axis.
bat3 complex An ER membrane insertion complex that acts by facilitating tail-anchored protein capture by ASNA1/TRC40. In mammals the complex contains Bat3, TRC35 and Ubl4A.
bax complex An oligomeric protein complex consisting of BAX, a member of the Bcl-2 family of anti- and proapoptotic regulators.
bbsome A protein complex that associates with the primary cilium and is involved in cilium biogenesis; consists of seven conserved proteins: BBS1, BBS2, BBS4, BBS5, BBS7, BBS8 and BBS9.
bcl-2 complex A homodimeric protein complex consisting of BCL-2, a member of the Bcl-2 family of anti- and proapoptotic regulators.
bcl-2 family protein complex A protein complex that consists of members of the Bcl-2 family of anti- and proapoptotic regulators. Bcl-2 proteins respond to cues from various forms of intracellular stress, such as DNA damage or cytokine deprivation, and interact with opposing family members to determine whether or not the caspase proteolytic cascade should be unleashed.
beta-catenin destruction complex A cytoplasmic protein complex containing glycogen synthase kinase-3-beta (GSK-3-beta), the adenomatous polyposis coli protein (APC), and the scaffolding protein axin, among others; phosphorylates beta-catenin, targets it for degradation by the proteasome.
beta-catenin-tcf7l2 complex A protein complex that contains beta-catenin and TCF7L2 (TCF4), binds to the TCF DNA motif within a promoter element, and is involved in the regulation of WNT target gene transcription.
beta-galactosidase complex A protein complex that possesses beta-galactosidase activity, i.e. catalyzes the hydrolysis of terminal non-reducing beta-D-galactose residues in beta-D-galactosides. In E. coli, the complex is a homotetramer; dimeric and hexameric beta-galactosidase complexes have been observed in other species.
beta-heterochromatin A diffusely banded region of heterochromatin located between euchromatin and alpha-heterochromatin in the polytene chromosome chromocenter; normally replicated during polytenization.
bid-bcl-2 complex A heterodimeric protein complex consisting of BID and BCL-2, members of the Bcl-2 family of anti- and proapoptotic regulators.
bim-bcl-2 complex A heterodimeric protein complex consisting of BIM and BCL-2, members of the Bcl-2 family of anti- and proapoptotic regulators.
bim-bcl-xl complex A heterodimeric protein complex consisting of BIM and BCL-xl, members of the Bcl-2 family of anti- and proapoptotic regulators.
biofilm matrix A structure lying external to bacterial cells. A biofilm is an aggregate of surface-associated bacteria, and the biofilm matrix is the envelope of polymeric substances that surrounds the bacteria.
bleb A cell extension characterized by rapid formation, rounded shape, and scarcity of organelles within the protrusions.
bloc complex Any of several protein complexes required for the biogenesis of specialized organelles of the endosomal-lysosomal system, such as melanosomes, platelet dense granules, and other related organelles; acronym for biogenesis of lysosomal-related organelles complex.
bloc-1 complex A protein complex required for the biogenesis of specialized organelles of the endosomal-lysosomal system, such as melanosomes and platelet dense granules. Many of the protein subunits are conserved between mouse and human; the mouse complex contains the Pallidin, Muted, Cappuccino, Dysbindin, Snapin, BLOS1, BLOS2, AND BLOS3 proteins.
bloc-2 complex A protein complex required for the biogenesis of specialized organelles of the endosomal-lysosomal system, such as melanosomes and platelet dense granules. The human complex contains the Hps3, Hps5, and Hps6 proteins; the mouse complex contains ru2 and ru.
blood microparticle A phospholipid microvesicle that is derived from any of several cell types, such as platelets, blood cells, endothelial cells, or others, and contains membrane receptors as well as other proteins characteristic of the parental cell. Microparticles are heterogeneous in size, and are characterized as microvesicles free of nucleic acids.
bmp receptor complex A protein complex that acts as a receptor for bone morphogenetic proteins (BMPs); a homo- or heterodimer of type I and/or type II BMP receptor subunits.
bounding membrane of organelle The lipid bilayer that forms the outer-most layer of an organelle.
box c/d snornp complex A ribonucleoprotein complex containing small nucleolar RNA of the box C/D type that can carry out ribose-2'-O-methylation of target RNAs.
box h/aca rnp complex A ribonucleoprotein complex that contains an RNA of the box H/ACA type, a subtype of the small nucleolar RNA (snoRNA) family. RNA pseudouridylation (isomerization of uridine to pseudouridine) is the major, and most likely the ancestral, function of H/ACA RNPs, although some have evolved other functions. Pseudouridylation targets include both large and small ribosomal RNAs (rRNAs), and on U2 small nuclear RNA (U2 snRNA).
box h/aca scarnp complex A box H/ACA RNP complex that is located in the Cajal body of the nucleoplasm. In higher eukaryotes, box H/ACA RNP located in Cajal bodies mediate pseudouridylation of spliceosomal snRNAs.
box h/aca snornp complex A box H/ACA RNP complex that is located in the nucleolus.
brahma complex A SWI/SNF-type complex that contains the ATPase product of the Drosophila brahma gene, or an ortholog thereof.
brca1-a complex A protein complex that contains the BRCA1-BARD1 heterodimer, RAP80/UIMC1, BRCC3/BRCC36, BRE/BRCC45, FAM175A/CCDC98/Abraxas and MERIT40/NBA1, and specifically recognizes and binds K63-linked polyubiquitin chains present on histone H2A and H2AX at DNA damage sites.
brca1-b complex A protein complex that contains the BRCA1-BARD1 heterodimer, BACH1 and TopBP1, and binds to DNA during S phase at DNA damage sites.
brca1-bard1 complex A heterodimeric complex comprising BRCA1 and BARD1, which possesses ubiquitin ligase activity and is involved in genome maintenance, possibly by functioning in surveillance for DNA damage.
brca1-c complex A protein complex that contains the BRCA1-BARD1 heterodimer, CtIP and Mre11/Rad50/NBS1 (M/R/N) complex, and binds to DNA at DNA damage sites. BRCA1-C binding ta damaged DNA is required for DNA damage-induced Chk1 phosphorylation and the G2/M transition checkpoint.
brisc complex A protein complex that contains the FAM175B/ABRO1, BRCC3/BRCC36, BRE/BRCC45 and MERIT40/NBA1 proteins, and specifically cleaves K63-linked polyubiquitin chains.
brush border Dense covering of microvilli on the apical surface of epithelial cells in tissues such as the intestine, kidney, and choroid plexus; the microvilli aid absorption by increasing the surface area of the cell.
brush border membrane The portion of the plasma membrane surrounding the brush border.
bunina body Small granular inclusions (about 1-3 microns in diameter) found in the anterior horn cells, and appearing either singly or in a group. Sometimes they are arranged in small beaded chains. Bunina bodies express cystatin C and consist of electron-dense amorphous material that contains tubules or vesicular structures. The amorphous material frequently includes a cytoplasmic island containing neurofilaments and other micro-organelles.
c bouton Synaptic bouton found in spinal cord on the soma and proximal dendrites of motor neurons.
c zone A region of the A band in which myosin-binding protein C is located and that can be seen by electron microscopy. This is a functional zone that also includes myosin.
c-fiber The axon of a dorsal root ganglion cell that are responsive to pain and temperature. C-fibers are small in diameter (0.2-1.5 um) and unmyelinated.
caf-1 complex A conserved heterotrimeric protein complex that promotes histone H3 and H4 deposition onto newly synthesized DNA during replication or DNA repair; specifically facilitates replication-dependent nucleosome assembly with the major histone H3 (H3.1). In many species the CAF-1 subunits are designated p150, p60, and p48.
cajal body A class of nuclear body, first seen after silver staining by Ramon y Cajal in 1903, enriched in small nuclear ribonucleoproteins, and certain general RNA polymerase II transcription factors; ultrastructurally, they appear as a tangle of coiled, electron-dense threads roughly 0.5 micrometers in diameter; involved in aspects of snRNP biogenesis; the protein coilin serves as a marker for Cajal bodies. Some argue that Cajal bodies are the sites for preassembly of transcriptosomes, unitary particles involved in transcription and processing of RNA.
cak-ercc2 complex A protein complex formed by the association of the cyclin-dependent protein kinase activating kinase (CAK) holoenzyme complex with ERCC2.
calcineurin complex A heterodimeric calcium ion and calmodulin dependent protein phosphatase composed of catalytic and regulatory subunits; the regulatory subunit is very similar in sequence to calmodulin.
calcium channel complex An ion channel complex through which calcium ions pass.
calcium- and calmodulin-dependent protein kinase complex An enzyme complex which in eukaryotes is composed of four different chains: alpha, beta, gamma, and delta. The different isoforms assemble into homo- or heteromultimeric holoenzymes composed of 8 to 12 subunits. Catalyzes the phosphorylation of proteins to O-phosphoproteins.
calyx of held The terminal specialization of a calyciferous axon which forms large synapses in the mammalian auditory central nervous system.
capitate projection Simple or compound process of epithelial glial cells with a spherical head that inserts into photoreceptor axons. Capitate projections have only been observed in Brachycera (flies).
capsomere Any of the protein subunits that comprise the closed shell or coat (capsid) of certain viruses.
capsule A protective structure surrounding some fungi and bacteria, attached externally to the cell wall and composed primarily of polysaccharides. Capsules are highly organized structures that adhere strongly to cells and cannot be easily removed. Capsules play important roles in pathogenicity, preventing phagocytosis by other cells, adherance, and resistance to dessication.
carbamoyl-phosphate synthase complex A protein complex that catalyzes the formation of carbamoyl phosphate; comprises a small subunit that binds and cleaves glutamine, and a large subunit that accepts the ammonia group cleaved from glutamine, binds all of the remaining substrates and effectors, and carries out all of the other catalytic events.
carboxy-terminal domain protein kinase complex A protein complex that phosphorylates amino acid residues of RNA polymerase II C-terminal domain repeats; phosphorylation occurs mainly on Ser2 and Ser5.
carboxysome An organelle found in the Cyanobacteria consisting of a proteinaceous coat and enzymes for the fixation of carbon dioxide including mechanisms for the concentration of carbonate to increase the efficiency of fixation under low-carbon dioxide conditions.
casparian strip Region of plant cell wall specialised to act as a seal to prevent back leakage of secreted material (analogous to tight junction between epithelial cells). Found particularly where root parenchymal cells secrete solutes into xylem vessels. The barrier is composed of suberin; a fatty substance, containing long chain fatty acids and fatty esters, also found in the cell walls of cork cells (phellem) in higher plants.
catalytic complex A protein complex which is capable of catalytic activity.
catalytic step 1 spliceosome A spliceosomal complex that is formed by the displacement of the two snRNPs from the precatalytic spliceosome; three snRNPs including U5 remain associated with the mRNA. This complex, sometimes called the activated spliceosome, is the catalytically active form of the spliceosome, and includes many proteins in addition to those found in the associated snRNPs.
catenin complex Complex of peripheral cytoplasmic proteins (alpha-, beta- and gamma-catenin) that interact with the cytoplasmic region of uvomorulin/E-cadherin to connect it to the actin cytoskeleton.
catenin-tcf7l2 complex A protein complex that contains a catenin and TCF7L2 (TCF4), binds to the TCF DNA motif within a promoter element, and is involved in the regulation of WNT target gene transcription.
cation channel complex An ion channel complex through which cations pass.
cation-transporting atpase complex Protein complex that carries out the reaction: ATP + H2O + cation(out) = ADP + phosphate + cation(in).
catsper complex A sperm-specific voltage-gated calcium channel that controls the intracellular calcium ion concentration and, thereby, the swimming behavior of sperm. Consists of a heteromeric tetramer surrounding a calcium ion- selective pore. May also contain additional auxiliary subunits.
caveola A membrane raft that forms small pit, depression, or invagination that communicates with the outside of a cell and extends inward, indenting the cytoplasm and the cell membrane. Examples include any of the minute pits or incuppings of the cell membrane formed during pinocytosis. Such caveolae may be pinched off to form free vesicles within the cytoplasm.
caveolar macromolecular signaling complex A complex composed of proteins required for beta adrenergic receptor activation of protein kinase A. It includes the Cav 12. subunit of L-type calcium channel, protein kinase A regulatory subunit 2(PKAR2), adenyl cyclase, beta-adrenergic receptor, G-alpha-S, protein phosphatase 2A (PP2A) and caveolin 3 (CAV3).
cbf3 complex A multisubunit protein complex that binds to centromeric DNA and initiates kinetochore assembly. In yeast, this complex consists of four subunits, namely Ctf13p, Skp1p, Cep3p and Cbf2p.
cbm complex A protein complex comprising Carma1, Bcl10 and MALT1; plays a role in signal transduction during NF-kappaB activation.
ccr4-not complex The evolutionarily conserved CCR4-NOT complex is involved in several aspects of mRNA metabolism, including repression and activation of mRNA initiation, control of mRNA elongation, and the deadenylation and subsequent degradation of mRNA. In Saccharomyces the CCR4-NOT complex comprises a core complex of 9 proteins (Ccr4p, Caf1p, Caf40p, Caf130p, Not1p, Not2p, Not3p, Not4p, and Not5p), Caf4p, Caf16p, and several less well characterized proteins.
ccr4-not core complex The core of the CCR4-NOT complex. In Saccharomyces the CCR4-NOT core complex comprises Ccr4p, Caf1p, Caf40p, Caf130p, Not1p, Not2p, Not3p, Not4p, and Not5p.
cd40 receptor complex A protein complex that contains at least CD40 (a cell surface receptor of the tumour necrosis factor receptor (TNFR) superfamily), and other signaling molecules.
cd95 death-inducing signaling complex A protein complex formed upon binding of Fas/CD95/APO-1 to its ligand. The complex includes FADD/Mort1, procaspase-8/10 and c-FLIP in addition to the ligand-bound receptor.
cdc42 gtpase complex A protein complex formed by the association of the small GTPase Cdc42 with additional proteins. In Schizosaccharomyces the complex contains the Cdc42, Ras1, Scd1, Scd2, andShk1 proteins, and functions in the Ras1-Scd GTPase signalling pathway.
cdc73/paf1 complex A multiprotein complex that associates with RNA polymerase II and general RNA polymerase II transcription factor complexes and may be involved in both transcriptional initiation and elongation. In Saccharomyces the complex contains Paf1p, Cdc73p, Ctr9p, Rtf1p, and Leo1p.
cell The basic structural and functional unit of all organisms. Includes the plasma membrane and any external encapsulating structures such as the cell wall and cell envelope.
cell body The portion of a cell bearing surface projections such as axons, dendrites, cilia, or flagella that includes the nucleus, but excludes all cell projections.
cell body fiber A neuron projection that is found in unipolar neurons and corresponds to the region between the cell body and the point at which the single projection branches.
cell body membrane The plasma membrane of a cell that bears surface projections such as axons, dendrites, cilia, or flagella, excluding the plasma membrane on cell projections.
cell cortex The region of a cell that lies just beneath the plasma membrane and often, but not always, contains a network of actin filaments and associated proteins.
cell cortex part Any constituent part of the cell cortex, the region of a cell that lies just beneath the plasma membrane and often, but not always, contains a network of actin filaments and associated proteins.
cell division site The eventual plane of cell division (also known as cell cleavage or cytokinesis) in a dividing cell. In Eukaryotes, the cleavage apparatus, composed of septin structures and the actomyosin contractile ring, forms along this plane, and the mitotic, or meiotic, spindle is aligned perpendicular to the division plane. In bacteria, the cell division site is generally located at mid-cell and is the site at which the cytoskeletal structure, the Z-ring, assembles.
cell division site part Any constituent part of the cell division plane, the eventual plane of cell division in a dividing cell.
cell envelope An envelope that surrounds a bacterial cell and includes the cytoplasmic membrane and everything external, encompassing the periplasmic space, cell wall, and outer membrane if present.
cell envelope sec protein transport complex A transmembrane protein complex involved in the translocation of proteins across the cytoplasmic membrane. In Gram-negative bacteria, Sec-translocated proteins are subsequently secreted via the type II, IV, or V secretion systems. Sec complex components include SecA, D, E, F, G, Y and YajC.
cell hair A long, thin cell projection that contains F-actin and tubulin, with microtubules centrally located and F-actin peripherally located.
cell junction A cellular component that forms a specialized region of connection between two cells or between a cell and the extracellular matrix. At a cell junction, anchoring proteins extend through the plasma membrane to link cytoskeletal proteins in one cell to cytoskeletal proteins in neighboring cells or to proteins in the extracellular matrix.
cell leading edge The area of a motile cell closest to the direction of movement.
cell outer membrane A lipid bilayer that forms the outermost membrane of the cell envelope; enriched in polysaccharide and protein; the outer leaflet of the membrane contains specific lipopolysaccharide structures.
cell part Any constituent part of a cell, the basic structural and functional unit of all organisms.
cell periphery The part of a cell encompassing the cell cortex, the plasma membrane, and any external encapsulating structures.
cell plate The nascent cell membrane and cell wall structure that forms between two daughter nuclei near the center of a dividing plant cell. It develops at the equitorial region of the phragmoplast. It grows outwards to join with the lateral walls and form two daughter cells.
cell pole Either of two different areas at opposite ends of an axis of a cell.
cell projection A prolongation or process extending from a cell, e.g. a flagellum or axon.
cell projection cytoplasm All of the contents of a cell projection, excluding the plasma membrane surrounding the projection.
cell projection membrane The portion of the plasma membrane surrounding a cell surface projection.
cell projection part Any constituent part of a cell projection, a prolongation or process extending from a cell, e.g. a flagellum or axon.
cell septum A structure composed of peptidoglycan and often chitin in addition to other materials. It usually forms perpendicular to the long axis of a cell or hypha and grows centripetally from the cell wall to the center of the cell and often functions in the compartmentalization of a cell into two daughter cells.
cell surface The external part of the cell wall and/or plasma membrane.
cell surface furrow A furrow that may be found on the cell surface. Examples are the cleavage furrow observed during cytokinesis in animal cells, and the cingulum and sulcus found in some dinoflagellates.
cell tip The region at either end of the longest axis of a cylindrical or elongated cell.
cell trailing edge The area of a motile cell opposite to the direction of movement.
cell trailing edge membrane The portion of the plasma membrane surrounding the trailing edge of a motile cell.
cell wall The rigid or semi-rigid envelope lying outside the cell membrane of plant, fungal, most prokaryotic cells and some protozoan parasites, maintaining their shape and protecting them from osmotic lysis. In plants it is made of cellulose and, often, lignin; in fungi it is composed largely of polysaccharides; in bacteria it is composed of peptidoglycan; in protozoan parasites such as Giardia species, it's made of carbohydrates and proteins.
cell wall part Any constituent part of the cell wall, the rigid or semi-rigid envelope lying outside the cell membrane of plant, fungal, and most prokaryotic cells, maintaining their shape and protecting them from osmotic lysis.
cell-cell adherens junction An adherens junction which connects a cell to another cell.
cell-cell contact zone Extended zone of intimate apposition between two cells containing one or more types of intercellular junctions, e.g., the intercalated disk of muscle.
cell-cell junction A cell junction that forms a connection between two cells; excludes direct cytoplasmic junctions such as ring canals.
cell-substrate adherens junction An adherens junction which connects a cell to the extracellular matrix.
cell-substrate junction A cell junction that forms a connection between a cell and the extracellular matrix.
cellular bud A protuberance from a cell of an organism that reproduces by budding, which will grow larger and become a separate daughter cell after nuclear division, cytokinesis, and cell wall formation (when appropriate). The daughter cell may completely separate from the mother cell, or the mother and daughter cells may remain associated.
cellular bud membrane The portion of the plasma membrane surrounding a cellular bud.
cellular bud neck The constriction between the mother cell and daughter cell (bud) in an organism that reproduces by budding.
cellular bud tip The end of a cellular bud distal to the site of attachment to the mother cell.
cellular_component The part of a cell or its extracellular environment in which a gene product is located. A gene product may be located in one or more parts of a cell and its location may be as specific as a particular macromolecular complex, that is, a stable, persistent association of macromolecules that function together.
cellulose microfibril A microfibril composed of cellulose arranged in orthogonal layers. Cellulose is a straight chain polysaccharide composed of B(14) linked glucose subunits. It is a major component of plant cell walls. Higher plant microfibrils are about 10nm in diameter and extremely long in relation to their width. The cellulose molecules are oriented parallel to the long axis of the microfibril in a paracrystalline array, which provides great tensile strength. The microfibrils are held in place by the wall matrix and their orientation is closely controlled by the cell.
cellulose synthase complex A large, multimeric protein complex, organized in a rosette, which catalyzes the biosynthesis of cellulose for the plant cell wall.
cellulosome An extracellular multi-enzyme complex containing up to 11 different enzymes aligned on a non-catalytic scaffolding glycoprotein. Functions to hydrolyze cellulose.
cenp-a containing nucleosome A form of nucleosome located only at the centromere, in which the histone H3 is replaced by the variant form CENP-A (sometimes known as CenH3).
central element A structural unit of the synaptonemal complex found between the lateral elements.
central vacuole A membrane-enclosed sac that takes up most of the volume of a mature plant cell. Functions include storage, separation of toxic byproducts, and cell growth determination.
centralspindlin complex A heterotetrameric protein complex playing a key role in the formation of the central spindle in mitosis. Made up of two molecules each of a mitotic kinesin (ZEN-4 in Caenorhabditis elegans or MKLP1 in mammals) and of two molecules each of a GTPase activating protein (GAP) factor (CYK-4 in Caenorhabditis elegans or MgcRacGAP in mammals).
centriolar satellite A small (70-100 nm) cytoplasmic granule that contains a number of centrosomal proteins; centriolar satellites traffic toward microtubule minus ends and are enriched near the centrosome.
centriole A cellular organelle, found close to the nucleus in many eukaryotic cells, consisting of a small cylinder with microtubular walls, 300-500 nm long and 150-250 nm in diameter. It contains nine short, parallel, peripheral microtubular fibrils, each fibril consisting of one complete microtubule fused to two incomplete microtubules. Cells usually have two centrioles, lying at right angles to each other. At division, each pair of centrioles generates another pair and the twin pairs form the pole of the mitotic spindle.
centrosomal corona An amorphous structure surrounding the core of the centrosome, from which microtubules are nucleated; contains gamma-tubulin.
centrosome A structure comprised of a core structure (in most organisms, a pair of centrioles) and peripheral material from which a microtubule-based structure, such as a spindle apparatus, is organized. Centrosomes occur close to the nucleus during interphase in many eukaryotic cells, though in animal cells it changes continually during the cell-division cycle.
cerebellar mossy fiber An axon arising from cerebellar projecting cells in the cochlea, vestibular nuclei, spinal cord, reticular formation, cerebellar nuclei and basilar pontine nuclei. Mossy fibers enter through all three cerebellar peduncles and send collaterals to the deep cerebellar nuclei, then branch in the white matter and terminate in the granule cell layer. Through this branching, a given mossy fiber can innervate several folia. Mossy fibers synapse on granule cells. The synaptic contacts are made at enlargements along the length of the mossy fiber called mossy fiber rosettes. The enlargements of the rosettes give the axons as mossy appearance in Golgi stained preparations.
cerf complex An ISWI complex that contains an ATPase subunit of the ISWI family (specifically SNF2L in mammals, which contain two ISWI homologs) and a CECR2 homolog. In mammals, CERF is involved in regulation of transcription from RNA polymerase II promoters.
chaperonin-containing t-complex A multisubunit ring-shaped complex that mediates protein folding in the cytosol without a cofactor.
chd-type complex A SWI/SNF-type complex that contains a subunit from the CHD(Chromodomain helicase DNA-binding) family. The CHD family is characterized by two signature sequence motifs: tandem chromodomains located in the N-terminal region, and the SNF2-like ATPase domain located in the central region of the protein structure.
checkpoint clamp complex Conserved heterotrimeric complex of PCNA-like proteins that is loaded onto DNA at sites of DNA damage.
chiasma A connection formed between chromatids, visible during meiosis, thought to be the point of the interchange involved in crossing-over.
chitosome An intracellular membrane-bounded particle found in fungi and containing chitin synthase; it synthesizes chitin microfibrils. Chitin synthase activity exists in chitosomes and they are proposed to act as a reservoir for regulated transport of chitin synthase enzymes to the division septum.
chloride channel complex An ion channel complex through which chloride ions pass.
chloroplast A chlorophyll-containing plastid with thylakoids organized into grana and frets, or stroma thylakoids, and embedded in a stroma.
chloroplast atp synthase complex The protein complex that catalyzes the phosphorylation of ADP to ATP in chloroplasts.
chloroplast chromosome A circular DNA molecule containing chloroplast encoded genes.
chloroplast envelope The double lipid bilayer enclosing the chloroplast and separating its contents from the rest of the cytoplasm; includes the intermembrane space.
chloroplast inner membrane The inner, i.e. lumen-facing, lipid bilayer of the chloroplast envelope; also faces the chloroplast stroma.
chloroplast intermembrane space The region between the inner and outer lipid bilayers of a chloroplast envelope.
chloroplast large ribosomal subunit The large subunit of a ribosome contained within a chloroplast.
chloroplast membrane Either of the lipid bilayers that surround a chloroplast and form the chloroplast envelope.
chloroplast nucleoid The region of a chloroplast to which the DNA is confined.
chloroplast outer membrane The outer, i.e. cytoplasm-facing, lipid bilayer of the chloroplast envelope.
chloroplast part Any constituent part of a chloroplast, a chlorophyll-containing plastid with thylakoids organized into grana and frets, or stroma thylakoids, and embedded in a stroma.
chloroplast photosystem i Photosystem located in the chloroplast that functions as a light-dependent plastocyanin-ferredoxin oxidoreductase, transferring electrons from plastocyanin to ferredoxin. An example of this is found in Arabidopsis thaliana.
chloroplast photosystem ii An integral chloroplast membrane complex containing the P680 reaction center. In the light, PSII functions as a water-plastoquinone oxidoreductase, transferring electrons from water to plastoquinone.
chloroplast ribosome A ribosome contained within a chloroplast.
chloroplast ribulose bisphosphate carboxylase complex A complex, located in the chloroplast, containing either both large and small subunits or just small subunits which carries out the activity of producing 3-phosphoglycerate from carbon dioxide and ribulose-1,5-bisphosphate. An example of this component is found in Arabidopsis thaliana.
chloroplast small ribosomal subunit The small subunit of a ribosome contained within a chloroplast.
chloroplast starch grain Plant storage body for amylose and amylopectin, 1-100um in diameter, and located in chloroplasts. Also contains small amounts of enzymes, amino acids, lipids and nucleic acids. The shape of the grain varies widely amongst species, but is often spherical or disk-shaped.
chloroplast stroma The space enclosed by the double membrane of a chloroplast but excluding the thylakoid space. It contains DNA, ribosomes and some temporary products of photosynthesis.
chloroplast thylakoid Sac-like membranous structures (cisternae) in a chloroplast combined into stacks (grana) and present singly in the stroma (stroma thylakoids or frets) as interconnections between grana. An example of this component is found in Arabidopsis thaliana.
chloroplast thylakoid lumen The cavity enclosed within the chloroplast thylakoid membrane. An example of this component is found in Arabidopsis thaliana.
chloroplast thylakoid membrane The pigmented membrane of a chloroplast thylakoid. An example of this component is found in Arabidopsis thaliana.
chlorosome A large enclosure of aggregated pigment, typically bacteriochlorophyll c (BChl c), that acts as a light-harvesting antenna structure and is characteristic of green photosynthetic bacteria (e.g. Chlorobiaceae). The BChl aggregates are organized into lamellar elements by pigment-pigment rather than pigment-protein interactions. Chlorosomes also contain BChl a, carotenoids, quinones, lipids, and proteins, and are attached to the cytoplasmic membrane via a BChl a-containing protein baseplate.
chlorosome envelope The structure, composed of a monolayer of glycolipids with embedded proteins, that encloses the pigments and other contents of the chlorosome.
chorion A protective, noncellular membrane that surrounds the eggs of various animals including insects and fish.
chrac An ISWI complex that contains an ATPase subunit of the ISWI family (SNF2H in mammals, Isw2 in S. cerevisiae), an ACF1 homolog, and additional small histone fold subunits (generally two of these, but Xenopus has only one and some additional non-conserved subunits). CHRAC plays roles in the regulation of RNA polymerase II transcription and in DNA replication and repair.
chromaffin granule Specialized secretory vesicle found in the cells of adrenal glands and various other organs, which is concerned with the synthesis, storage, metabolism, and secretion of epinephrine and norepinephrine.
chromaffin granule membrane The lipid bilayer surrounding a chromaffin granule, a specialized secretory vesicle found in the cells of adrenal glands and various other organs, which is concerned with the synthesis, storage, metabolism, and secretion of epinephrine and norepinephrine.
chromatin The ordered and organized complex of DNA, protein, and sometimes RNA, that forms the chromosome.
chromatin silencing complex Any protein complex that mediates changes in chromatin structure that result in transcriptional silencing.
chromatoid body A ribonucleoprotein complex found in the cytoplasm of male germ cells, composed of exceedingly thin filaments that are consolidated into a compact mass or into dense strands of varying thickness that branch to form an irregular network. Contains mRNAs, miRNAs, and protein components involved in miRNA processing (such as Argonaute proteins and the endonuclease Dicer) and in RNA decay (such as the decapping enzyme DCP1a and GW182).
chromocenter A region in which centric, heterochromatic portions of one or more chromosomes form a compact structure.
chromoplast A plastid containing pigments other than chlorophyll, usually yellow and orange carotenoid pigments.
chromoplast envelope The double lipid bilayer enclosing the chromoplast and separating its contents from the rest of the cytoplasm; includes the intermembrane space.
chromoplast membrane Either of the lipid bilayers that surround a chromoplast and form the chromoplast envelope.
chromosomal part Any constituent part of a chromosome, a structure composed of a very long molecule of DNA and associated proteins (e.g. histones) that carries hereditary information.
chromosomal region Any subdivision of a chromosome along its length.
chromosome A structure composed of a very long molecule of DNA and associated proteins (e.g. histones) that carries hereditary information.
chromosome passenger complex A eukaryotically conserved protein complex that localizes to kinetochores in early mitosis, the spindle mid-zone in anaphase B and to the telophase midbody. It has been proposed that the passenger complex coordinates various events based on its location to different structures during the course of mitosis. Complex members include the BIR-domain-containing protein Survivin, Aurora kinase, INCENP and Borealin.
chromosome segregation-directing complex A trimeric protein complex which in E. coli is composed of the subunits MreB, MreC and MreD. The complex directs longitudinal cell wall synthesis, maintaining cell morphology.
chromosome, centromeric region The region of a chromosome that includes the centromeric DNA and associated proteins. In monocentric chromosomes, this region corresponds to a single area of the chromosome, whereas in holocentric chromosomes, it is evenly distributed along the chromosome.
chromosome, telomeric region The terminal region of a linear chromosome that includes the telomeric DNA repeats and associated proteins.
chylomicron A large lipoprotein particle (diameter 75-1200 nm) composed of a central core of triglycerides and cholesterol surrounded by a protein-phospholipid coating. The proteins include one molecule of apolipoprotein B-48 and may include a variety of apolipoproteins, including APOAs, APOCs and APOE. Chylomicrons are found in blood or lymph and carry lipids from the intestines into other body tissues.
chylomicron remnant A lipoprotein particle that is derived from a mature chylomicron particle by the removal of triglycerides from the chylomicron core by lipoprotein lipase and the subsequent loss of surface components. It characteristically contains apolipoprotein E (APOE) and is cleared from the blood by the liver.
cia complex The cytosolic iron-sulfur protein assembly (CIA) complex mediates the incorporation of iron-sulfur clusters into apoproteins involved in DNA metabolism and genomic integrity.
ciliary basal body A membrane-tethered, short cylindrical array of microtubules and associated proteins found at the base of a eukaryotic cilium (also called flagellum) that is similar in structure to a centriole and derives from it. The cilium basal body is the site of assembly and remodelling of the cilium and serves as a nucleation site for axoneme growth. As well as anchoring the cilium, it is thought to provide a selective gateway regulating the entry of ciliary proteins and vesicles by intraflagellar transport.
ciliary cytoplasm All of the contents of a cilium, excluding the plasma membrane surrounding the cilium.
ciliary membrane The portion of the plasma membrane surrounding a cilium.
ciliary neurotrophic factor receptor complex A protein complex that acts as a receptor for the cytokine ciliary neurotrophic factor (CNTF). In humans the receptor complex is a hexamer composed of two molecules each of CNTF and CNTFR and one molecule each of gp130 and LIFR.
ciliary part Any constituent part of a cilium, a specialized eukaryotic organelle that consists of a filiform extrusion of the cell surface. Each cilium is bounded by an extrusion of the cytoplasmic (plasma) membrane, and contains a regular longitudinal array of microtubules, anchored basally in a centriole.
ciliary pocket Invagination of the plasma membrane from which a cilium (also called flagellum) protrudes.
ciliary pocket membrane That part of the plasma membrane found in the ciliary pocket (also called flagellar pocket).
ciliary rootlet A cytoskeleton-like structure, originating from the basal body at the proximal end of a cilium, and extending proximally toward the cell nucleus. Rootlets are typically 80-100 nm in diameter and contain cross striae distributed at regular intervals of approximately 55-70 nm.
ciliary transition zone A region of the cilium between the basal body and proximal segment that is characterized by Y-shaped assemblages that connect axonemal microtubules to the ciliary membrane. The ciliary transition zone appears to function as a gate that controls ciliary membrane composition.
cilium A specialized eukaryotic organelle that consists of a filiform extrusion of the cell surface and of some cytoplasmic parts. Each cilium is largely bounded by an extrusion of the cytoplasmic (plasma) membrane, and contains a regular longitudinal array of microtubules, anchored to a basal body.
cis-golgi network The network of interconnected tubular and cisternal structures located at the convex side of the Golgi apparatus, which abuts the endoplasmic reticulum.
cis-golgi network membrane The lipid bilayer surrounding any of the compartments that make up the cis-Golgi network.
classical lewy body Cytoplasmic inclusion, 5 to 15 micrometers in diameter, with a dense core surrounded by a halo of 10 to 20 nm wide radially oriented alpha-synuclein fibrils.
clathrin adaptor complex A membrane coat adaptor complex that links clathrin to a membrane.
clathrin coat A membrane coat found on coated pits and some coated vesicles; consists of polymerized clathrin triskelions, each comprising three clathrin heavy chains and three clathrin light chains, linked to the membrane via one of the AP adaptor complexes.
clathrin coat of coated pit The coat found on coated pits and the coated vesicles derived from coated pits; comprises clathrin and the AP-2 adaptor complex.
clathrin coat of endocytic vesicle A clathrin coat found on an endocytic vesicle.
clathrin coat of trans-golgi network vesicle A clathrin coat found on a vesicle of the trans-Golgi network.
clathrin complex A protein complex that consists of three clathrin heavy chains and three clathrin light chains, organized into a symmetrical three-legged structure called a triskelion. In clathrin-coated vesicles clathrin is the main component of the coat and forms a polymeric mechanical scaffold on the vesicle surface.
clathrin vesicle coat A clathrin coat found on a vesicle.
clathrin-coated endocytic vesicle A clathrin-coated, membrane-bounded intracellular vesicle formed by invagination of the plasma membrane around an extracellular substance.
clathrin-coated endocytic vesicle membrane The lipid bilayer surrounding a clathrin-coated endocytic vesicle.
clathrin-coated vesicle A vesicle with a coat formed of clathrin connected to the membrane via one of the clathrin adaptor complexes.
clathrin-coated vesicle membrane The lipid bilayer surrounding a clathrin-coated vesicle.
cleavage body A nuclear body that contains proteins involved in pre-mRNA 3'-end cleavage and polyadenylation, such as DDX1, CSTF2 and CPSFs, as well as the transcription factors TFIIE and TFIIF. Cleavage bodies are localized adjacent to Cajal bodies and are involved in mRNA3'-end processing.
cleavage furrow In animal cells, the first sign of cleavage, or cytokinesis, is the appearance of a shallow groove in the cell surface near the old metaphase plate. A contractile ring containing actin and myosin is located just inside the plasma membrane at the location of the furrow. Ring contraction is associated with centripetal growth of the membrane that deepens the cleavage furrow and divides the cytoplasm of the two daughter cells. While the term 'cleavage furrow' was initially associated with animal cells, such a structure occurs in many other types of cells, including unicellular protists.
climbing fiber The axon of inferior olive neuron that projects to the cerebellar cortex, largely via the inferior cerebellar peduncle. They range in diameter from 1-3 um and are myelinated until they enter the granule cell layer. They give off collaterals to the deep cerebellar nuclei. They synapse extensively with the dendrites of Purkinje cells in the molecular layer, where each fiber branches repeatedly to climb along the Purkinje cell dendritic tree. Each Purkinje cell is innervated by only a single climbing fiber.
clrc ubiquitin ligase complex An cullin-dependent E3 ubiquitin ligase/histone H3-K9 methyltransferase complex essential for heterochromatin assembly by RNAi.
cmg complex A protein complex that contains the GINS complex, Cdc45p, and the heterohexameric MCM complex, and that is involved in unwinding DNA during replication.
coated membrane A single or double lipid bilayer with any of several different proteinaceous coats that can associate with membranes. Membrane coats include those formed by clathrin plus an adaptor complex, the COPI and COPII complexes.
coated pit A part of the endomembrane system in the form of an invagination of a membrane upon which a clathrin coat forms, and that can be converted by vesicle budding into a clathrin-coated vesicle. Coated pits form on the plasma membrane, where they are involved in receptor-mediated selective transport of many proteins and other macromolecules across the cell membrane, in the trans-Golgi network, and on some endosomes.
coated vesicle Small membrane-bounded organelle formed by pinching off of a coated region of membrane. Some coats are made of clathrin, whereas others are made from other proteins.
coated vesicle membrane The lipid bilayer surrounding a coated vesicle.
cohesin complex A protein complex that is required for sister chromatid cohesion in eukaryotes. The cohesin complex forms a molecular ring complex, and is composed of structural maintenance of chromosomes (SMC) and kleisin proteins. For example, in yeast, the complex is composed of the SMC proteins Smc1p and Smc3p, and the kleisin protein Scc1p. In vertebrates, the complex is composed of the SMC1 (SMC1A or SMC1B) and SMC3 heterodimer attached via their hinge domains to a kleisin (RAD21, REC8 or RAD21L) which links them, and one STAG protein (STAG1, STAG2 or STAG3).
cohesin core heterodimer The core heterodimer of a cohesin complex; a structure required for sister chromatid cohesion in eukaryotes.
collagen and cuticulin-based cuticle extracellular matrix A collagen and cuticulin-based noncellular, multilayered structure that is synthesized by an underlying ectodermal (hypodermal) cell layer. The cuticle serves essential functions in body morphology, locomotion, and environmental protection. An example of this component is found in Caenorhabditis elegans.
collagen and cuticulin-based cuticle extracellular matrix part Any constituent part of the collagen and cuticulin-based cuticle extracellular matrix, a collagen and cuticulin-based noncellular, multilayered structure that is synthesized by an underlying ectodermal (hypodermal) cell layer.
collagen trimer A protein complex consisting of three collagen chains assembled into a left-handed triple helix. These trimers typically assemble into higher order structures.
collagen type i trimer A collagen trimer containing alpha(I) chains. The most common form of type I collagen is a heterotrimer containing two alpha1(I) chains and one alpha2(I) chain; homotrimers containing three alpha1(I) chains are also found. Type I collagen triple helices associate to form banded fibrils.
collagen type ii trimer A collagen homotrimer of alpha1(II) chains; type II collagen triple helices associate to form fibrils.
collagen type iii trimer A collagen homotrimer of alpha1(III) chains; type III collagen triple helices associate to form fibrils.
collagen type iv trimer A collagen heterotrimer containing type IV alpha chains; [alpha1(IV)]2alpha2(IV) trimers are commonly observed, although more type IV alpha chains exist and may be present in type IV trimers; type IV collagen triple helices associate to form 3 dimensional nets within basement membranes.
collagen type ix trimer A collagen heterotrimer containing type IX alpha chains in alpha1(IX)alpha2(IX)alpha3(IX) trimers; type IX collagen triple helices associate to form a structure that links glycosaminoglycans to type II collagen fibrils.
collagen type v trimer A collagen heterotrimer containing type V alpha chains; [alpha1(V)]2alpha2(V) and alpha1(V)alpha2(V)alpha3(V) trimers have been observed; type V collagen triple helices associate to form fibrils.
collagen type vi trimer A collagen heterotrimer containing type VI alpha chains in alpha1(VI)alpha2(VI)alpha3(VI) trimers; type VI collagen triple helices associate to form beaded fibrils.
collagen type vii trimer A collagen homotrimer of alpha1(VII) chains; type VII collagen triple helices form antiparallel dimer, which in turn associate laterally to form anchoring fibrils that connect type IV collagen in the basal lamina to plaques in the underlying connective tissue. It binds laminin.
collagen type viii trimer A collagen heterotrimer containing type VIII alpha chains; [alpha1(VIII)2]alpha2(VIII) and alpha1(VIII)[alpha2(VIII)]2 trimers have been observed; type VIII collagen triple helices associate to form regular hexagonal nets.
collagen type x trimer A collagen homotrimer of alpha1(X) chains; type X collagen triple helices form hexagonal networks (sheets).
collagen type xi trimer A collagen heterotrimer containing type XI alpha chains in alpha1(XI)alpha2(XI)alpha3(XI) trimers; type XI collagen triple helices associate to form fibrils.
collagen type xii trimer A collagen homotrimer of alpha1(XII) chains; type XII collagen triple helices may link sheet-forming or fibrillar collagens to other structures.
collagen type xiii trimer A collagen homotrimer of alpha1(XIII) chains; type XIII collagen triple helices span the plasma membrane.
collagen type xiv trimer A collagen homotrimer of alpha1(XIV) chains; type XIV collagen triple helices may link sheet-forming or fibrillar collagens to other structures.
collagen type xv trimer A collagen homotrimer of alpha1(XV) chains; a chondroitin sulfate proteoglycan often found in specialized basement membranes where it bridges between fibrils.
collagen type xvi trimer A collagen trimer containing alpha(XVI) chains; type XVI trimers can associate with microfibrils.
collagen type xvii trimer A collagen homotrimer of alpha1(XVII) chains; type XVII collagen triple helices span the plasma membrane and associate with hemidesmosomes and the basal lamina where they bind laminin.
collagen type xviii trimer A collagen homotrimer of alpha1(XVIII) chains.
coma complex A multiprotein complex in yeast consisting of Ctf19p, Okp1p, Mcm21p, and Ame1p. This complex bridges the subunits that are in contact with centromeric DNA and the subunits bound to microtubules during kinetochore assembly.
commitment complex A spliceosomal complex that is formed by association of the U1 snRNP with the 5' splice site of an unspliced intron in an RNA transcript.
compact myelin The portion of the myelin sheath in which layers of cell membrane are tightly juxtaposed, completely excluding cytoplasm. The juxtaposed cytoplasmic surfaces form the major dense line, while the juxtaposed extracellular surfaces form the interperiod line visible in electron micrographs.
complement component c1 complex A protein complex composed of six subunits of C1q, each formed of the three homologous polypeptide chains C1QA, C1QB, and C1QB, and tetramer of two C1QR and two C1QS polypeptide chains.
complex laminated body A cytoplasmic inclusion body found in some lateral geniculate neurons and composed of sheets of tubules (25 nm in diameter) separated by dense material (about 75 nm wide), which together with the tubules whorl give a structure resembling a fingerprint.
condensed chromosome A highly compacted molecule of DNA and associated proteins resulting in a cytologically distinct structure.
condensed chromosome inner kinetochore The region of a condensed chromosome kinetochore closest to centromeric DNA; in mammals the CREST antigens (CENP proteins) are found in this layer; this layer may help define underlying centromeric chromatin structure and position of the kinetochore on the chromosome.
condensed chromosome kinetochore A multisubunit complex that is located at the centromeric region of a condensed chromosome and provides an attachment point for the spindle microtubules.
condensed chromosome outer kinetochore The region of a condensed chromosome kinetochore most external to centromeric DNA; this outer region mediates kinetochore-microtubule interactions.
condensed chromosome, centromeric region The region of a condensed chromosome that includes the centromere and associated proteins, including the kinetochore. In monocentric chromosomes, this region corresponds to a single area of the chromosome, whereas in holocentric chromosomes, it is evenly distributed along the chromosome.
condensed nuclear chromosome A highly compacted molecule of DNA and associated proteins resulting in a cytologically distinct structure that remains in the nucleus.
condensed nuclear chromosome kinetochore A multisubunit complex that is located at the centromeric region of a condensed chromosome in the nucleus and provides an attachment point for the spindle microtubules.
condensed nuclear chromosome outer kinetochore The region of a condensed nuclear chromosome kinetochore most external to centromeric DNA; this outer region mediates kinetochore-microtubule interactions.
condensed nuclear chromosome, centromeric region The region of a condensed chromosome in the nucleus that includes the centromere and associated proteins, including the kinetochore. In monocentric chromosomes, this region corresponds to a single area of the chromosome, whereas in holocentric chromosomes, it is evenly distributed along the chromosome.
condensin complex A multisubunit protein complex that plays a central role in chromosome condensation.
condensin core heterodimer The core heterodimer of a condensin complex, a multisubunit protein complex that plays a central role in chromosome condensation.
cone cell pedicle A specialized axon terminus which is produced by retinal cone cells. Pedicles are large, conical, flat end-feet (8-10 micrometers diameter) of the retinal cone axon that lie more or less side by side on the same plane at the outer edge of the outer plexiform layer (OPL).
connexon complex An assembly of six molecules of connexin, made in the Golgi apparatus and subsequently transported to the plasma membrane, where docking of two connexons on apposed plasma membranes across the extracellular space forms a gap junction.
conoid A spiral cytoskeletal structure located at the apical end of the apical complex in some apicomplexan parasites. Fibers form a left-handed spiral, and are comprised of tubulin protofilaments organized in a ribbon-like structure that differs from the conventional tubular structure characteristic of microtubules.
contact site Sites of close apposition of the inner and outer mitochondrial membrane.
contractile fiber Fibers, composed of actin, myosin, and associated proteins, found in cells of smooth or striated muscle.
contractile fiber part Any constituent part of a contractile fiber, a fiber composed of actin, myosin, and associated proteins, found in cells of smooth or striated muscle.
contractile ring A cytoskeletal structure composed of filamentous protein that forms beneath the membrane of many cells or organelles, in the plane of cell or organelle division. Ring contraction is associated with centripetal growth of the membrane that divides the cytoplasm of the two daughter cells or organelles.
contractile vacuolar membrane The lipid bilayer surrounding the contractile vacuole.
contractile vacuole A specialized vacuole of eukaryotic cells, especially Protozoa, that fills with water from the cytoplasm and then discharges this externally by the opening of contractile vacuole pores. Its function is probably osmoregulatory.
contractile vacuole pore Stable structure that regulates the flow of liquid between the contractile vacuole and the surrounding medium.
cop9 signalosome A protein complex that catalyzes the deneddylation of proteins, including the cullin component of SCF ubiquitin E3 ligase; deneddylation increases the activity of cullin family ubiquitin ligases. The signalosome is involved in many regulatory process, including some which control development, in many species; also regulates photomorphogenesis in plants; in many species its subunits are highly similar to those of the proteasome.
copi vesicle coat One of two multimeric complexes that forms a membrane vesicle coat. The mammalian COPI subunits are called alpha-, beta-, beta'-, gamma-, delta-, epsilon- and zeta-COP. Vesicles with COPI coats are found associated with Golgi membranes at steady state.
copi-coated vesicle A vesicle with a coat formed of the COPI coat complex proteins. COPI-coated vesicles are found associated with Golgi membranes at steady state, are involved in Golgi to endoplasmic reticulum (retrograde) vesicle transport, and possibly also in intra-Golgi transport.
copi-coated vesicle membrane The lipid bilayer surrounding a COPI-coated vesicle.
copii vesicle coat One of two multimeric complexes that forms a membrane vesicle coat. COPII is best characterized in S. cerevisiae, where the subunits are called Sar1p, Sec13p, Sec31p, Sec23p, and Sec24p. Vesicles with COPII coats are found associated with endoplasmic reticulum (ER) membranes at steady state.
core mediator complex A protein complex that interacts with the carboxy-terminal domain of the largest subunit of RNA polymerase II and plays an active role in transducing the signal from a transcription factor to the transcriptional machinery. The core mediator complex has a stimulatory effect on basal transcription, and contains most of the same subdomains as the larger form of mediator complex -- a head domain comprising proteins known in Saccharomyces as Srb2, -4, and -5, Med6, -8, and -11, and Rox3 proteins; a middle domain comprising Med1, -4, and -7, Nut1 and -2, Cse2, Rgr1, Soh1, and Srb7 proteins; and a tail consisting of Gal11p, Med2p, Pgd1p, and Sin4p -- but lacks the regulatory subcomplex comprising Ssn2, -3, and -8, and Srb8 proteins. Metazoan core mediator complexes have similar modular structures and include homologs of yeast Srb and Med proteins.
core tfiih complex The 7 subunit core of TFIIH that is a part of either the general transcription factor holo-TFIIH or the nucleotide-excision repair factor 3 complex. In S. cerevisiae/humans the complex is composed of: Ssl2/XPB, Tfb1/p62, Tfb2/p52, Ssl1/p44, Tfb4/p34, Tfb5/p8 and Rad3/XPD.
cornified envelope A type of plasma membrane that has been modified through addition of distinct intracellular and extracellular components, including ceramide, found in cornifying epithelial cells (corneocytes).
cortical actin cytoskeleton The portion of the actin cytoskeleton, comprising filamentous actin and associated proteins, that lies just beneath the plasma membrane.
cortical cytoskeleton The portion of the cytoskeleton that lies just beneath the plasma membrane.
cortical endoplasmic reticulum A cortical network of highly dynamic tubules that are juxtaposed to the plasma membrane and undergo ring closure and tubule-branching movements.
cortical granule A secretory vesicle that is stored under the cell membrane of an egg. These vesicles fuse with the egg plasma membrane as part of egg activation and are part of the block to polyspermy.
cortical layer of collagen and cuticulin-based cuticle extracellular matrix The cuticle layer that lies directly beneath the lipid-containing epicuticle. The cortical layer contains collagens and insoluble, non-collagenous cuticulins and is characterized by a distinct annular pattern consisting of regularly spaced annular ridges delineated by annular furrows. An example of this component is found in Caenorhabditis elegans.
cortical lewy body Cytoplasmic inclusion similar to a classical Lewy body but lacking a halo of protein fibrils.
cortical microtubule Arrays of microtubules underlying and connected to the plasma membrane in the cortical cytosol.
cortical microtubule cytoskeleton The portion of the microtubule cytoskeleton that lies just beneath the plasma membrane.
corvet complex A multimeric protein complex that acts as an endosomal tethering complex (CORVET = class C core vacuole/endosome tethering) by cooperating with Rab GTPases to capture endosomal vesicles and trap them prior to the action of SNAREs; the complex is involved in endo-lysosomal biogenesis and required for transport between endosome and vacuole. The Saccharomyces cerevisiae complex contains Vps8p, Vps3p, Pep5p, Vps16p, Pep3p, and Vps33p.
costamere Regular periodic sub membranous arrays of vinculin in skeletal and cardiac muscle cells, these arrays link Z-discs to the sarcolemma and are associated with links to extracellular matrix.
creatine kinase complex A protein complex having creatine kinase activity.
crystalloid A transient, cytoplasmic organelle found in Plasmodium species that resembles a cytoplasmic inclusion body and whose function is poorly understood. Crystalloids form in ookinetes and disappear after ookinete-to-oocyst transformation.
ctf18 rfc-like complex A heptameric complex related to replication factor C, which loads the DNA polymerase processivity factor proliferating cell nuclear antigen (PCNA) onto DNA and plays a vital role in chromosome cohesion. In Saccharomyces the subunits are known as Ctf18p, Rfc2p, Rfc3p, Rfc4p, Rfc5p, Dcc1p, and Ctf8p.
cugbp1-eif2 complex A protein complex that contains the eukaryotic translation initiation factor 2 complex (EIF2), CUG binding protein 1, and several endoplasmic reticulum proteins; the complex is involved in the regulation of translation.
cul2-ring ubiquitin ligase complex A ubiquitin ligase complex in which a cullin from the Cul2 subfamily and a RING domain protein form the catalytic core; substrate specificity is conferred by an elongin-BC adaptor and a SOCS/BC box protein.
cul3-ring ubiquitin ligase complex A ubiquitin ligase complex in which a cullin from the Cul3 subfamily and a RING domain protein form the catalytic core; substrate specificity is conferred by a BTB-domain-containing protein.
cul4-ring e3 ubiquitin ligase complex A ubiquitin ligase complex in which a cullin from the Cul4 family and a RING domain protein form the catalytic core; substrate specificity is conferred by an adaptor protein.
cul4a-ring e3 ubiquitin ligase complex A ubiquitin ligase complex in which a cullin from the Cul4A subfamily and a RING domain protein form the catalytic core; substrate specificity is conferred by an adaptor protein.
cul4b-ring e3 ubiquitin ligase complex A ubiquitin ligase complex in which a cullin from the Cul4B subfamily and a RING domain protein form the catalytic core; substrate specificity is conferred by unknown subunits.
cul5-ring ubiquitin ligase complex A ubiquitin ligase complex in which a cullin from the Cul5 subfamily and a RING domain protein form the catalytic core; substrate specificity is conferred by an elongin-BC adaptor and a SOCS/BC box protein.
cul7-ring ubiquitin ligase complex A ubiquitin ligase complex in which a cullin from the Cul7 subfamily and a RING domain protein form the catalytic core; substrate specificity is conferred by a Skp1 linker and an F-box protein.
cullin-ring ubiquitin ligase complex Any ubiquitin ligase complex in which the catalytic core consists of a member of the cullin family and a RING domain protein; the core is associated with one or more additional proteins that confer substrate specificity.
curi complex A protein complex that is involved in the transcription of ribosomal genes. In Saccharomyces this complex consists of Ckb2p, Utp22p, Rrp7p and Ifh1p.
cuticular plate A dense network of actin filaments found beneath the apical cell surface of hair cells, and into which stereocilia are inserted.
cvt complex A protein complex that is involved in the CVT pathway. In budding yeast, the CVT complex consists of multimers of preApe1p.
cvt vesicle A cytosolic vesicle that is enclosed by a double membrane and is implicated in the cytoplasm to vacuole targeting pathway. These vesicles are found in the yeast S. cerevisiae, and contain vacuolar hydrolases, aminopeptidase I (Ape1p) and alpha-mannosidase (Ams1p).
cyanelle A plastid that contains unstacked, phycobilisome-bearing thylakoid membranes and is surrounded by a double membrane with a peptidoglycan layer in the intermembrane space between the two envelope membranes. Cyanelles are characteristic of algae in the class Glaucophyta, and may represent an ancestral form of plastid.
cyanelle ribonuclease p complex A ribonuclease P complex located in the cyanelle, where it catalyzes the 5' endonucleolytic cleavage of precursor tRNAs to yield mature tRNAs. The best characterized cyanelle ribonuclease P complex, from the alga Cyanophora paradoxa, contains a single RNA molecule that is necessary but not sufficient for catalysis, and several protein molecules.
cyclin a1-cdk2 complex A protein complex consisting of cyclin A1 and cyclin-dependent kinase 2 (CDK2). Cyclins are characterized by periodicity in protein abundance throughout the cell cycle. Cyclin-dependent kinases represent a family of serine/threonine protein kinases that become active upon binding to a cyclin regulatory partner.
cyclin a2-cdk1 complex A protein complex consisting of cyclin A2 and cyclin-dependent kinase 1 (CDK1). Cyclins are characterized by periodicity in protein abundance throughout the cell cycle. Cyclin-dependent kinases represent a family of serine/threonine protein kinases that become active upon binding to a cyclin regulatory partner.
cyclin a2-cdk2 complex A protein complex consisting of cyclin A2 and cyclin-dependent kinase 2 (CDK2). Cyclins are characterized by periodicity in protein abundance throughout the cell cycle. Cyclin-dependent kinases represent a family of serine/threonine protein kinases that become active upon binding to a cyclin regulatory partner.
cyclin b1-cdk1 complex A protein complex consisting of cyclin B1 and cyclin-dependent kinase 1 (CDK1). Cyclins are characterized by periodicity in protein abundance throughout the cell cycle. Cyclin-dependent kinases represent a family of serine/threonine protein kinases that become active upon binding to a cyclin regulatory partner.
cyclin b2-cdk1 complex A protein complex consisting of cyclin B2 and cyclin-dependent kinase 1 (CDK1). Cyclins are characterized by periodicity in protein abundance throughout the cell cycle. Cyclin-dependent kinases represent a family of serine/threonine protein kinases that become active upon binding to a cyclin regulatory partner.
cyclin d1-cdk4 complex A protein complex consisting of cyclin D1 and cyclin-dependent kinase 4 (CDK4). Cyclins are characterized by periodicity in protein abundance throughout the cell cycle. Cyclin-dependent kinases represent a family of serine/threonine protein kinases that become active upon binding to a cyclin regulatory partner.
cyclin d1-cdk6 complex A protein complex consisting of cyclin D1 and cyclin-dependent kinase 6 (CDK6). Cyclins are characterized by periodicity in protein abundance throughout the cell cycle. Cyclin-dependent kinases represent a family of serine/threonine protein kinases that become active upon binding to a cyclin regulatory partner.
cyclin d2-cdk4 complex A protein complex consisting of cyclin D2 and cyclin-dependent kinase 4 (CDK4). Cyclins are characterized by periodicity in protein abundance throughout the cell cycle. Cyclin-dependent kinases represent a family of serine/threonine protein kinases that become active upon binding to a cyclin regulatory partner.
cyclin d2-cdk6 complex A protein complex consisting of cyclin D2 and cyclin-dependent kinase 6 (CDK6). Cyclins are characterized by periodicity in protein abundance throughout the cell cycle. Cyclin-dependent kinases represent a family of serine/threonine protein kinases that become active upon binding to a cyclin regulatory partner.
cyclin d3-cdk4 complex A protein complex consisting of cyclin D3 and cyclin-dependent kinase 4 (CDK4). Cyclins are characterized by periodicity in protein abundance throughout the cell cycle. Cyclin-dependent kinases represent a family of serine/threonine protein kinases that become active upon binding to a cyclin regulatory partner.
cyclin d3-cdk6 complex A protein complex consisting of cyclin D3 and cyclin-dependent kinase 6 (CDK6). Cyclins are characterized by periodicity in protein abundance throughout the cell cycle. Cyclin-dependent kinases represent a family of serine/threonine protein kinases that become active upon binding to a cyclin regulatory partner.
cyclin e1-cdk2 complex A protein complex consisting of cyclin E1 and cyclin-dependent kinase 2 (CDK2). Cyclins are characterized by periodicity in protein abundance throughout the cell cycle. Cyclin-dependent kinases represent a family of serine/threonine protein kinases that become active upon binding to a cyclin regulatory partner.
cyclin e2-cdk2 complex A protein complex consisting of cyclin E2 and cyclin-dependent kinase 2 (CDK2). Cyclins are characterized by periodicity in protein abundance throughout the cell cycle. Cyclin-dependent kinases represent a family of serine/threonine protein kinases that become active upon binding to a cyclin regulatory partner.
cyclin k-cdk12 complex A protein complex consisting of cyclin Kand cyclin-dependent kinase 12 (CDK12). Cyclins are characterized by periodicity in protein abundance throughout the cell cycle. Cyclin-dependent kinases represent a family of serine/threonine protein kinases that become active upon binding to a cyclin regulatory partner.
cyclin k-cdk13 complex A protein complex consisting of cyclin Kand cyclin-dependent kinase 13 (CDK13). Cyclins are characterized by periodicity in protein abundance throughout the cell cycle. Cyclin-dependent kinases represent a family of serine/threonine protein kinases that become active upon binding to a cyclin regulatory partner.
cyclin-dependent protein kinase activating kinase holoenzyme complex A cyclin-dependent kinase activating kinase complex capable of activating cyclin-dependent kinases by threonine phosphorylation, thus regulating cell cycle progression. consists of a kinase, cyclin and optional assembly factors, in human CDK7, CCNH and MNAT1. CAK activity is itself regulated throughout the cell cycle by T-loop phosphorylation of its kinase component (CDK7 in human). Phosphorylation of serine residues during mitosis inactivates the enzyme. Also capable of CAK phosphorylating the carboxyl-terminal domain (CTD) of RNA polymerase II and other transcription activating proteins, as part of the general transcription factor TFIIH.
cyclin-dependent protein kinase holoenzyme complex Cyclin-dependent protein kinases (CDKs) are enzyme complexes that contain a kinase catalytic subunit associated with a regulatory cyclin partner.
cysteine synthase complex Cysteine synthase is a multienzyme complex made up, in E. coli, of the heteromeric hexamer serine acetyltransferase and the homodimer O-acetylserine (thiol)-lyase A.
cytochrome b6f complex Complex that transfers electrons from reduced plastoquinone to oxidized plastocyanin and translocates protons from the stroma to the lumen. The complex contains a core structure of three catalytic subunits: cytochrome b, the Rieske iron sulfur protein (ISP), and cytochrome f, which are arranged in an integral membrane-bound dimeric complex; additional subunits are present, and vary among different species.
cytochrome complex A protein complex in which at least one of the proteins is a cytochrome, i.e. a heme-containing protein involved in catalysis of redox reactions.
cytolytic granule A specialized secretory lysosome that is present in cells with cytolytic capability such as cytotoxic T lymphocytes and natural killer cells. Cytolytic granules mediate the storage and regulated excretion of lytic molecules for killing of target cells.
cytoneme A long, thin, polarized cell projection that contains actin and can extend for distances many times the diameter of the cell. Cytonemes represent extensions of cell cytoplasm and typically have a diameter of approximately 0.2um.
cytoophidium A subcellular filamentary structure where CTP synthase is compartmentalized in a range of organisms including bacteria, yeast, fruit fly, rat and human.
cytoplasm All of the contents of a cell excluding the plasma membrane and nucleus, but including other subcellular structures.
cytoplasmic chromatin The ordered and organized complex of DNA, protein, and sometimes RNA, that forms the chromosome in the cytoplasm.
cytoplasmic chromosome A chromosome found in the cytoplasm.
cytoplasmic dynein complex Any dynein complex that catalyzes movement along a cytoplasmic microtubule; cytoplasmic dynein complexes participates in many transport activities in eukaryotes, such as mRNA localization, intermediate filament transport, nuclear envelope breakdown, apoptosis, transport of centrosomal proteins, mitotic spindle assembly, virus transport, kinetochore functions, and movement of signaling and spindle checkpoint proteins. Subunits associated with the dynein heavy chain mediate association between dynein heavy chain and cargoes,and may include light chains and light intermediate chains.
cytoplasmic exosome (rnase complex) Complex of 3'-5' exoribonucleases found in the cytoplasm.
cytoplasmic membrane-bounded vesicle A membrane-bounded vesicle found in the cytoplasm of the cell.
cytoplasmic membrane-bounded vesicle lumen The volume enclosed by the membrane of a cytoplasmic membrane-bounded vesicle.
cytoplasmic microtubule Any microtubule in the cytoplasm of a cell.
cytoplasmic mrna processing body A focus in the cytoplasm where mRNAs may become inactivated by decapping or some other mechanism. mRNA processing and binding proteins are localized to these foci.
cytoplasmic nucleosome A complex comprised of DNA wound around a multisubunit core and associated proteins, which forms the primary packing unit of DNA in the cytoplasm into higher order structures.
cytoplasmic origin of replication recognition complex A multisubunit complex that is located at the replication origins of a chromosome in the cytoplasm.
cytoplasmic part Any constituent part of the cytoplasm, all of the contents of a cell excluding the plasma membrane and nucleus, but including other subcellular structures.
cytoplasmic ribonucleoprotein granule A ribonucleoprotein granule located in the cytoplasm.
cytoplasmic scf ubiquitin ligase complex A ubiquitin ligase complex, located in the cytoplasm, in which a cullin from the Cul1 subfamily and a RING domain protein form the catalytic core; substrate specificity is conferred by a Skp1 adaptor and an F-box protein. SCF complexes are involved in targeting proteins for degradation by the proteasome. The best characterized complexes are those from yeast and mammals (with core subunits named Cdc53/Cul1, Rbx1/Hrt1/Roc1).
cytoplasmic side of membrane The side of a membrane that faces the cytoplasm.
cytoplasmic side of plasma membrane The leaflet the plasma membrane that faces the cytoplasm and any proteins embedded or anchored in it or attached to its surface.
cytoplasmic stress granule A dense aggregation in the cytosol composed of proteins and RNAs that appear when the cell is under stress.
cytoplasmic u snrnp body A ribonucleoprotein complex that can be visualized as a focus in the cytoplasm, and contains uridine-rich small nuclear ribonucleoproteins (U snRNPs) and essential snRNP assembly factors. These U bodies are invariably found in association with P bodies.
cytoplasmic ubiquitin ligase complex A ubiquitin ligase complex found in the cytoplasm.
cytoplasmic vesicle A vesicle formed of membrane or protein, found in the cytoplasm of a cell.
cytoplasmic vesicle membrane The lipid bilayer surrounding a cytoplasmic vesicle.
cytoplasmic vesicle part Any constituent part of cytoplasmic vesicle, a vesicle formed of membrane or protein, found in the cytoplasm of a cell.
cytoproct Stable, specialized structure for extrusion of waste by the cell into the surrounding medium.
cytoskeletal calyx A large cytoskeletal structure located at the posterior end of the perinuclear theca of a mammalian sperm head. The nucleus is tightly associated with the calyx, which contains calicin and basic cylicin proteins.
cytoskeletal part Any constituent part of the cytoskeleton, a cellular scaffolding or skeleton that maintains cell shape, enables some cell motion (using structures such as flagella and cilia), and plays important roles in both intra-cellular transport (e.g. the movement of vesicles and organelles) and cellular division. Includes constituent parts of intermediate filaments, microfilaments, microtubules, and the microtrabecular lattice.
cytoskeleton Any of the various filamentous elements that form the internal framework of cells, and typically remain after treatment of the cells with mild detergent to remove membrane constituents and soluble components of the cytoplasm. The term embraces intermediate filaments, microfilaments, microtubules, the microtrabecular lattice, and other structures characterized by a polymeric filamentous nature and long-range order within the cell. The various elements of the cytoskeleton not only serve in the maintenance of cellular shape but also have roles in other cellular functions, including cellular movement, cell division, endocytosis, and movement of organelles.
cytosol The part of the cytoplasm that does not contain organelles but which does contain other particulate matter, such as protein complexes.
cytosolic aryl hydrocarbon receptor complex An aryl hydrocarbon receptor complex found in the cytosol, in which the ligand-binding subunit AhR is not bound to ligand; consists of AhR, two molecules of HSP90, the protein kinase c-Src, and the immunophilin XAP2/AIP.
cytosolic creatine kinase complex A dimeric protein complex having creatine kinase activity.
cytosolic large ribosomal subunit The large subunit of a ribosome located in the cytosol.
cytosolic part Any constituent part of cytosol, that part of the cytoplasm that does not contain membranous or particulate subcellular components.
cytosolic proteasome complex A proteasome complex found in the cytosol of a cell.
cytosolic ribosome A ribosome located in the cytosol.
cytosolic small ribosomal subunit The small subunit of a ribosome located in the cytosol.
cytosolic trna wobble base thiouridylase complex A complex of two proteins involved in the thiolation of U34 in glutamate, lysine, and glutamine tRNAs of eukaryotes.
cytostome Stable, specialized structure for the ingestion of food by the cell into phagosomes.
dash complex A large protein complex, containing around 8-10 subunits in yeast, including Duo1p, Dam1p, Dad1p and Ask1p. The complex forms part of the kinetochore, associates with microtubules when the kinetochore attaches to the spindle, and plays a role in spindle attachment, chromosome segregation and spindle stability.
dbf4-dependent protein kinase complex A heterodimeric protein complex required for the activation of DNA replication origins; comprises a catalytic subunit and a regulatory subunit (in Saccharomyces, Cdc7p and Dbf4p, respectively); complexes identified in other species generally contain proteins related to the Saccharomyces proteins.
dbird complex A protein complex that associates with mRNP particles and RNA polymerase II and is proposed to integrate transcript elongation with the regulation of alternative splicing. In humans it is composed of the proteins KIAA1967/DBC1 and ZNF326/ZIRD.
death-inducing signaling complex A protein complex formed by the association of signaling proteins with a death receptor upon ligand binding. The complex includes procaspases and death domain-containing proteins in addition to the ligand-bound receptor, and may control the activation of caspases 8 and 10.
decaprenyl diphosphate synthase complex A complex that possesses di-trans,poly-cis-decaprenylcistransferase activity; involved in ubiquinone biosynthesis.
deep fiber Inward projections of the cytoskeletal structures of the oral apparatus, which form a fiber that extends past the cytostome into the cytoplasm.
delta1 complex A protein complex that consists of homodimer of the Notch ligand Delta1.
dendriole Small dendrites that makes up a brush structure found as the terminal specialization of a dendrite of a unipolar brush cell (UBC).
dendrite A neuron projection that has a short, tapering, often branched, morphology, receives and integrates signals from other neurons or from sensory stimuli, and conducts a nerve impulse towards the axon or the cell body. In most neurons, the impulse is conveyed from dendrites to axon via the cell body, but in some types of unipolar neuron, the impulse does not travel via the cell body.
dendrite cytoplasm All of the contents of a dendrite, excluding the surrounding plasma membrane.
dendrite membrane The portion of the plasma membrane surrounding a dendrite.
dendrite terminus A structure at the distal end of a dendrite adapted to carry out a specific function, e.g. dendriole.
dendritic branch A dendrite arising from another dendrite.
dendritic branch point The part of a dendrite where the cell projection branches, giving rise to a dendritic branch.
dendritic growth cone The migrating motile tip of a growing nerve cell dendrite.
dendritic microtubule Any microtubule in a dendrite, a neuron projection.
dendritic shaft Cylindric portion of the dendrite, directly stemming from the perikaryon, and carrying the dendritic spines.
dendritic spine Protrusion from a dendrite. Spines are specialised subcellular compartments involved in the synaptic transmission. They are linked to the dendritic shaft by a restriction. Because of their bulb shape, they function as a biochemical and an electrical compartment. Spine remodeling is though to be involved in synaptic plasticity.
dendritic spine head Distal part of the dendritic spine, that carries the post-synaptic density.
dendritic spine membrane The portion of the plasma membrane surrounding a dendritic spine.
dendritic spine neck Part of the dendritic spine that connects the dendritic shaft to the head of the dendritic spine.
dendritic tree The entire complement of dendrites for a neuron, consisting of each primary dendrite and all its branches.
dendritic tuft The terminal specialization found in some types of dendrites which consists of numerous small terminal branches, giving the dendrite a tufted appearance.
dense body An electron dense body which may contain granules.
dense core granule Electron-dense organelle with a granular internal matrix; contains proteins destined to be secreted.
dense core granule membrane The lipid bilayer surrounding a dense core granule.
dense fibrillar component A structure found in the nucleolus, which contains newly synthesized preribosomal RNA (pre-rRNA) and a collection of proteins.
dense nuclear body A location in the host cell nucleus where viral proteins colocalize late in infection prior to the onset of viral DNA synthesis. More than one site can be present simultaneously.
dentate gyrus mossy fiber Distinctive, unmyelinated axons produced by granule cells.
desmosome A cell-cell junction in which: on the cytoplasmic surface of each interacting plasma membrane is a dense plaque composed of a mixture of intracellular anchor proteins; a bundle of keratin intermediate filaments is attached to the surface of each plaque; transmembrane adhesion proteins of the cadherin family bind to the plaques and interact through their extracellular domains to hold the adjacent membranes together by a Ca2+-dependent mechanism.
dihydrolipoyl dehydrogenase complex A protein complex that possesses alpha-ketoglutarate dehydrogenase activity.
dimeric positive transcription elongation factor complex b A positive transcription elongation factor complex b that comprises two subunits; an example is the budding yeast complex containing Svg1p (also called Bur1p) and Bur2p.
discoidal high-density lipoprotein particle A newly formed high-density lipoprotein particle; consists of a phospholipid bilayer surrounded by two or more APOA1 molecules. The discoidal HDL particle is formed when lipid-free or lipid-poor APOA1 acquires phospholipids and unesterified cholesterol from either cell membranes or triglyceride-rich lipoproteins (undergoing lipolysis by lipoprotein lipase).
dna bending complex A protein-DNA complex that contains DNA in combination with a protein which binds to and bends DNA. Often plays a role in DNA compaction.
dna helicase complex A protein complex that possesses DNA helicase activity.
dna ligase iii-xrcc1 complex A protein complex that contains DNA ligase III and XRCC1, and is involved in base excision repair.
dna ligase iv complex A eukaryotically conserved protein complex that contains DNA ligase IV and is involved in DNA repair by non-homologous end joining; in addition to the ligase, the complex also contains XRCC4 or a homolog, e.g. Saccharomyces Lif1p.
dna packaging complex A protein complex that plays a role in the process of DNA packaging.
dna polymerase complex A protein complex that possesses DNA polymerase activity and is involved in template directed synthesis of DNA.
dna polymerase iii complex The DNA polymerase III holoenzyme is a complex that contains 10 different types of subunits. These subunits are organized into 3 functionally essential sub-assemblies: the pol III core, the beta sliding clamp processivity factor and the clamp-loading complex. The pol III core carries out the polymerase and the 3'-5' exonuclease proofreading activities. The polymerase is tethered to the template via the sliding clamp processivity factor. The clamp-loading complex assembles the beta processivity factor onto the primer template and plays a central role in the organization and communication at the replication fork.
dna polymerase processivity factor complex A protein complex which is capable of increasing the processivity of nucleotide polymerization by DNA polymerase as a part of DNA replication.
dna recombinase mediator complex A protein complex containing accessory proteins which bind a recombinase (e.g. Rad51) and bind single-stranded DNA (ssDNA), and promote nucleation of the recombinase onto ssDNA.
dna repair complex A protein complex involved in DNA repair processes including direct reversal, base excision repair, nucleotide excision repair, photoreactivation, bypass, double-strand break repair pathway, and mismatch repair pathway.
dna replication factor a complex A conserved heterotrimeric complex that binds nonspecifically to single-stranded DNA and is required for multiple processes in eukaryotic DNA metabolism, including DNA replication, DNA repair, and recombination. In all eukaryotic organisms examined the complex is composed of subunits of approximately 70, 30, and 14 kDa.
dna replication factor c complex A complex of five polypeptides in eukaryotes, and two in prokaryotes, that loads the DNA polymerase processivity factor proliferating cell nuclear antigen (PCNA) onto DNA, thereby permitting processive DNA synthesis catalyzed by DNA polymerase.
dna replication preinitiation complex A protein-DNA complex assembled at eukaryotic DNA replication origins immediately prior to the initiation of DNA replication. The preinitiation complex is formed by the assembly of additional proteins onto an existing prereplicative complex. In budding yeast, the additional proteins include Cdc45p, Sld2p, Sld3p, Dpb11p, DNA polymerases, and others; in fission yeast the GINS complex is present.
dna replication termination region A chromosomal region that contains fork pausing elements influencing the progression and merging of DNA replication forks.
dna viral genome A viral genome composed of deoxyribonucleic acid.
dna-dependent protein kinase complex A protein complex that is involved in the repair of DNA double-strand breaks and, in mammals, V(D)J recombination events. It consists of the DNA-dependent protein kinase catalytic subunit (DNA-PKcs) and the DNA end-binding heterodimer Ku.
dna-directed rna polymerase complex A protein complex that possesses DNA-directed RNA polymerase activity.
dna-directed rna polymerase ii, holoenzyme Large protein complex composed of the RNA polymerase core complex and a variety of other proteins including transcription factor complexes TFIIA, D, E, F, and H which are required for promoter recognition, and the Mediator subcomplex. Catalyzes the synthesis of eukaryotic pre-mRNA.
dna-directed rna polymerase v complex RNA polymerase V is a multisubunit RNA polymerase complex found in the nucleus of plants and involved in accumulation of siRNAs and in DNA methylation-dependent silencing of endogenous repeated sequences. Pol V is composed of subunits that are paralogous or identical to the 12 subunits of Pol II. Two large subunits comprise the most conserved portion including the catalytic site and share similarity with other eukaryotic and bacterial multisubunit RNA polymerases. The second largest subunit is also found in RNA polymerase IVa, while the largest subunit is found only in the IVa complex and contains an extended C-terminal domain (CTD) that includes multiple repeats of a 16 amino-acid consensus sequence as well as other sequences. The remainder of the complex is composed of smaller subunits.
doa10p ubiquitin ligase complex A multiprotein complex that recognizes and ubiquitinates membrane proteins with misfolded cytosolic domains during ER-associated protein degradation (ERAD). In S. cerevisiae, this complex contains the ubiquitin ligase Ssm4p/Doa10p.
dolipore septum A septum, or cross-wall, between two portions of a cell or hypha; contains a central pore around which the septum is swollen to form a barrel-shaped structure; pore is covered on each side of the septum by a septal pore cap (parenthosome).
dosage compensation complex A protein or protein-RNA complex that localizes to one or more of the sex chromosome(s), where it acts to normalize transcription between different sexes.
drm complex A transcriptional repressor complex that contains the lin-9, lin-35, lin-37, lin-52, lin-53, lin-5is involved in 4-, dpl-1 and efl-1 proteins, and is involved in cell fate specification.
dsc e3 ubiquitin ligase complex An E3 ubiquitin ligase complex localized to the ER and Golgi membrane. In fission yeast comprises Dsc1, 2, 3 and 4. Involved in the processes of fission yeast sre1 (human SREBP) transcriptional activator proteolytic cleavage, the multivesicular body (MVB) pathway, and a post-endoplasmic reticulum pathway for protein catabolism.
dsif complex A heterodimeric protein complex formed of Spt4 and Spt5 proteins which is expressed in eukaryotes from yeast to man. DSIF is an inhibitory elongation factor that promotes RNA polymerase II transcriptional pausing, but can also stimulate transcriptional elongation under certain conditions, and may play a role in RNA processing via its physical association with mRNA capping enzymes.
dsl1p complex A multisubunit tethering complex, i.e. a protein complex involved in mediating the initial interaction between vesicles and the membranes with which they fuse, that is involved in trafficking from the Golgi apparatus to the ER. In Saccharomyces cerevisiae the Dsl1p complex contains Dsl1p, Tip20p, and Sec39p.
dsrna viral genome A viral genome composed of double stranded RNA.
dubm complex A protein complex that forms part of SAGA-type complexes SAGA and SLIK, and mediates deubiquitination of histone H2B. In S. cerevisiae, the DUBm consists of the proteins Ubp8p, Sgf11p, Sus1p, and Sgf73p.
dynactin complex A 20S multiprotein assembly of total mass about 1.2 MDa that activates dynein-based activity in vivo. A large structural component of the complex is an actin-like 40 nm filament composed of actin-related protein, to which other components attach.
dynein complex Any of several large complexes that contain two or three dynein heavy chains and several light chains, and have microtubule motor activity.
dystrobrevin complex A protein complex comprising alpha- and beta-dystrobrevin; forms part of the dystrophin glycoprotein complex.
dystroglycan complex A protein complex that includes alpha- and beta-dystroglycan, which are alternative products of the same gene; the laminin-binding component of the dystrophin-associated glycoprotein complex, providing a link between the subsarcolemmal cytoskeleton (in muscle cells) and the extracellular matrix. Alpha-dystroglycan is an extracellular protein binding to alpha-laminin and to beta-dystroglycan; beta-dystroglycan is a transmembrane protein which binds alpha-dystroglycan and dystrophin.
dystrophin-associated glycoprotein complex A multiprotein complex that forms a strong mechanical link between the cytoskeleton and extracellular matrix; typical of, but not confined to, muscle cells. The complex is composed of transmembrane, cytoplasmic, and extracellular proteins, including dystrophin, sarcoglycans, dystroglycan, dystrobrevins, syntrophins, sarcospan, caveolin-3, and NO synthase.
early endosome A membrane-bounded organelle that receives incoming material from primary endocytic vesicles that have been generated by clathrin-dependent and clathrin-independent endocytosis; vesicles fuse with the early endosome to deliver cargo for sorting into recycling or degradation pathways.
early endosome membrane The lipid bilayer surrounding an early endosome.
early phagosome A membrane-bounded intracellular vesicle as initially formed upon the ingestion of particulate material by phagocytosis.
early phagosome membrane The lipid bilayer surrounding an early phagosome.
early recombination nodule An electron dense structure that is associated with meiotic chromosomes in leptotene or zygotene during meiosis I.
ectexine The outer part of the exine, which stains positively with basic fuchsin in optical microscopy and has higher electron density in conventionally prepared TEM sections.
ectoplasm Granule free cytoplasm, lying immediately below the plasma membrane.
egasyn-beta-glucuronidase complex A protein complex that contains beta-glucuronidase and the carboxyl esterase egasyn; formation of the complex causes beta-glucuronidase to be retained in the endoplasmic reticulum.
egfr-grb2-sos complex A protein complex that contains the epidermal growth factor receptor (EGFR), Grb2 and the guanine nucleotide exchange factor Sos (or an ortholog thereof, such as mSos1), and is involved in linking EGFR activation to the p21-Ras pathway.
egfr-shc-grb2-sos complex A protein complex that contains the epidermal growth factor receptor (EGFR), Grb2, the adaptor protein SHC and the guanine nucleotide exchange factor Sos (or an ortholog thereof, such as mSos1), and is involved in linking EGFR activation to the p21-Ras pathway.
egg coat A specialized extracellular matrix that surrounds the ovum of animals. The egg coat provides structural support and can play an essential role in oogenesis, fertilization and early development.
ego complex A vacuolar membrane-associated protein complex that is required for activation of microautophagy during exit from rapamycin-induced growth arrest. In budding yeast, S. cerevisiae, this complex includes Gtr1p, Gtr2p, Meh1p, and Slm4p.
eisosome A cell part that is composed of the eisosome membrane or MCC domain, a furrow-like plasma membrane sub-domain and associated integral transmembrane proteins, and the proteins (eisosome filaments) that form a scaffolding lattice on the cytoplasmic face. Eisosomes broadly affect overall plasma membrane organization.
ekc/keops complex A protein complex proposed to be involved in transcription as well as promoting telomere uncapping and telomere elongation. For example, in Saccharomyces cerevisiae the complex contains Bud32p, Kae1p, Gon7p, Cgi121p, and Pcc1p.
elaioplast A leucoplast in which oil is stored.
elastic fiber An extracellular matrix part that consists of an insoluble core of polymerized tropoelastin monomers and a surrounding mantle of microfibrils. Elastic fibers provide elasticity and recoiling to tissues and organs, and maintain structural integrity against mechanical strain.
electron transfer flavoprotein complex A protein complex containing flavin adenine dinucleotide (FAD) and acyl-CoA dehydrogenase, which form a system that oxidizes an acyl-CoA molecule and reduces ubiquinone and other acceptors in the mitochondrial electron transport system.
elg1 rfc-like complex A pentameric complex related to replication factor C, which loads the DNA polymerase processivity factor proliferating cell nuclear antigen (PCNA) onto DNA and has roles in telomere length regulation and other aspects of genome stability. In Saccharomyces the subunits are known as Elg1p, Rfc2p, Rfc3p, Rfc4p, and Rfc5p.
ell-eaf complex A heterodimeric protein complex that acts as an RNA polymerase II elongation factor; the complex is conserved from yeast to humans, and is present in S. pombe, but absent from S. cerevisiae.
elongator holoenzyme complex A heterohexameric protein complex that is involved in modification of wobble nucleosides in tRNA, and exerts direct effects on transcriptional elongation and exocytosis. The complex can associate physically with hyperphosphorylated RNA polymerase II; it contains two discrete heterotrimeric subcomplexes.
elongin complex A transcription elongation factor complex that suppresses RNA polymerase II pausing, and may act by promoting proper alignment of the 3'-end of nascent transcripts with the polymerase catalytic site. Consists of a transcriptionally active Elongin A subunit (abut 100 kDa)and two smaller Elongin B (about 18 kDa) and Elongin C (about 15 kDa)subunits.
endocytic patch The part of the cell cortex consisting of an aggregation of proteins that will give rise to an endocytic vesicle.
endocytic vesicle A membrane-bounded intracellular vesicle formed by invagination of the plasma membrane around an extracellular substance. Endocytic vesicles fuse with early endosomes to deliver the cargo for further sorting.
endocytic vesicle membrane The lipid bilayer surrounding an endocytic vesicle.
endolysosome An transient hybrid organelle formed by fusion of a late endosome with a lysosome, and in which active degradation takes place.
endolysosome membrane The lipid bilayer surrounding an endolysosome. An endolysosome is a transient hybrid organelle formed by fusion of a late endosome with a lysosome.
endomembrane system A collection of membranous structures involved in transport within the cell. The main components of the endomembrane system are endoplasmic reticulum, Golgi bodies, vesicles, cell membrane and nuclear envelope. Members of the endomembrane system pass materials through each other or though the use of vesicles.
endonuclear canal A membrane-bound structure present in the nucleus of a spermatozoon. There is variation in the number of endonuclear canals between sperm of different organisms, and some species lack these structures altogether. The endonuclear canal may provide a supporting role for the sperm nucleus, and originates during spermiogenesis from an invagination of the nuclear envelope.
endoplasmic reticulum The irregular network of unit membranes, visible only by electron microscopy, that occurs in the cytoplasm of many eukaryotic cells. The membranes form a complex meshwork of tubular channels, which are often expanded into slitlike cavities called cisternae. The ER takes two forms, rough (or granular), with ribosomes adhering to the outer surface, and smooth (with no ribosomes attached).
endoplasmic reticulum chaperone complex A protein complex that is located in the endoplasmic reticulum and is composed of chaperone proteins, including BiP, GRP94; CaBP1, protein disulfide isomerase (PDI), ERdj3, cyclophilin B, ERp72, GRP170, UDP-glucosyltransferase, and SDF2-L1.
endoplasmic reticulum exit site An endoplasmic reticulum part at which COPII-coated vesicles are produced.
endoplasmic reticulum lumen The volume enclosed by the membranes of the endoplasmic reticulum.
endoplasmic reticulum membrane The lipid bilayer surrounding the endoplasmic reticulum.
endoplasmic reticulum palmitoyltransferase complex A dimeric complex of the endoplasmic reticulum that catalyzes S-palmitoylation, the addition of palmitate (C16:0) or other long-chain fatty acids to proteins at a cysteine residue.
endoplasmic reticulum part Any constituent part of the endoplasmic reticulum, the irregular network of unit membranes, visible only by electron microscopy, that occurs in the cytoplasm of many eukaryotic cells. The membranes form a complex meshwork of tubular channels, which are often expanded into slitlike cavities called cisternae.
endoplasmic reticulum quality control compartment A subcompartment of the endoplasmic reticulum in which proteins with improper or incorrect folding accumulate. Enzymes in this compartment direct proteins with major folding problems to translocation to the cytosol and degradation, and proteins with minor folding problems to the ER, to interact with chaperon proteins.
endoplasmic reticulum sec complex An endoplasmic reticulum membrane-associated complex involved in the translocation of proteins that are targeted to the ER. In yeast, this complex consists of two subcomplexes, namely, the Sec61 complex and the Sec62/Sec63 complex.
endoplasmic reticulum tubular network An endoplasmic reticulum part that comprises the membranes with high curvature in cross-section.
endoplasmic reticulum-golgi intermediate compartment A complex system of membrane-bounded compartments located between endoplasmic reticulum (ER) and the Golgi complex, with a distinctive membrane protein composition; involved in ER-to-Golgi transport.
endoplasmic reticulum-golgi intermediate compartment membrane The lipid bilayer surrounding any of the compartments of the endoplasmic reticulum (ER)-Golgi intermediate compartment system.
endoribonuclease complex A protein complex which is capable of endoribonuclease activity.
endosomal part Any constituent part of an endosome, a membrane-bounded organelle to which materials ingested by endocytosis are delivered.
endosomal scaffold complex A protein complex that contains MAPKSP1 (MP1, Map2k1ip1) and ROBLD3 (p14, Mapbpip), is anchored to late endosomes, and is involved in selective activation of the ERK1 in ERK/MAPK signaling.
endosome A membrane-bounded organelle to which materials ingested by endocytosis are delivered.
endosome lumen The volume enclosed by the membrane of an endosome.
endosome membrane The lipid bilayer surrounding an endosome.
endospore coat The layer in a bacterial endospore that lies under the exosporium, and is impermeable to many toxic molecules. The coat may also contain enzymes that are involved in endospore germination.
endospore cortex A layer surrounding a bacterial endospore found inside the outer endospore membrane, but outside the membrane surrounding the endospore core. It consists of peptidoglycan of a different chemical nature than that found in vegetative cell walls which results in less cross-linking of peptidoglycan.
endospore external encapsulating structure The structures that lie outside the inner membrane and surround the entire endospore; consists of a peptidoglycan-containing inner layer (the endospore cortex) surrounded by a multilayered proteinaceous coat. An exosporium may be present as an extreme outer layer.
endothelial microparticle A blood microparticle that is derived from, and contains membrane receptors as well as other proteins characteristic of, an endothelial cell.
enhanceosome A protein-DNA complex formed by the association of a distinct set of general and specific transcription factors with a region of enhancer DNA. The cooperative assembly of an enhanceosome confers specificity of transcriptional regulation.
ensheathing process A cell projection (often from glial cells such as Schwann cells) that surrounds an unmyelinated axon or cell soma.
enterobactin synthetase complex A multienzyme complex usually composed of four proteins, EntB, EntD, EntE and EntF. Plays a role in the enterobactin biosynthesis pathway.
envelope A multilayered structure surrounding all or part of a cell; encompasses one or more lipid bilayers, and may include a cell wall layer; also includes the space between layers.
epidermal lamellar body A specialized secretory organelle found in keratinocytes and involved in the formation of an impermeable, lipid-containing membrane that serves as a water barrier and is required for correct skin barrier function.
epsilon dna polymerase complex A heterotetrameric DNA polymerase complex that catalyzes processive DNA synthesis in the absence of PCNA, but is further stimulated in the presence of PCNA. The complex contains a large catalytic subunit and three small subunits, and is best characterized in Saccharomyces, in which the subunits are named Pol2p, Dpb2p, Dpb3p, and Dpb4p. Some evidence suggests that DNA polymerase epsilon is the leading strand polymerase; it is also involved in nucleotide-excision repair and mismatch repair.
equatorial microtubule organizing center A microtubule organizing center formed by a band of gamma-tubulin that is recruited to a circumferential band of F-actin at the midpoint of a cell and which nucleates microtubules from the cell division site at the end of mitosis.
er body A novel compartment found in plant cells that is derived from the ER. The structures have a characteristic shape and size (10 mm long and 0.5 mm wide) and are surrounded with ribosomes. They have been found in Arabidopsis thaliana and related Brassicaceae species.
er membrane insertion complex A protein complex that is involved in the post-translational delivery of tail-anchored (TA) membrane proteins to the endoplasmic reticulum. TA membrane proteins, also called type II transmembrane proteins, contain a single C-terminal transmembrane region. Some ER membrane insertion complex subunits are conserved between different species such as mammals and budding yeast.
er membrane protein complex A transmembrane protein complex that is involved in protein folding in the endoplasmic reticulum. In S. cerevisiae, it has six members: EMC1, EMC2, AIM27, EMC4, KRE27, and EMC6.
er proteasome complex A proteasome found in the endoplasmic reticulum of a cell.
er to golgi transport vesicle A vesicle that mediates transport from the endoplasmic reticulum to the Golgi complex; bears a coat formed of the COPII coat complex proteins; such vesicles found associated with endoplasmic reticulum (ER) membranes at steady state, and are involved in ER to Golgi (anterograde) vesicle transport.
er to golgi transport vesicle membrane The lipid bilayer surrounding a vesicle transporting substances from the endoplasmic reticulum to the Golgi.
er ubiquitin ligase complex A ubiquitin ligase complex found in the ER.
er-mitochondrion membrane contact site A zone of apposition between endoplasmic-reticulum and mitochondrial membranes, structured by bridging complexes. These contact sites are thought to facilitate inter-organelle calcium and phospholipid exchange.
erbb4-egfr complex A heterodimeric complex between the tyrosine kinase receptors ERBB4 (also called HER4) and epidermal growth factor receptor (EGFR/ERBB1).
erbb4-erbb3 complex A heterodimeric complex between the tyrosine kinase receptors ERBB4 (also called HER4) and ERBB3 (also called HER3). ERBB3 has impaired kinase activity so relies on the kinase activity of its heterodimer partner for activation and signal transmission.
erbb4-erbb4 complex A homodimeric complex containing two monomers of the tyrosine kinase receptor ERBB4 (also called HER4).
ercc4-ercc1 complex A heterodimeric nucleotide-excision repair complex that has endonuclease activity specific for bubble structures characteristic of certain DNA lesions. The subunits are known as XPF/ERCC4 and ERCC1 in mammals, and Rad1p and Rad10p in S. cerevisiae.
ermes complex A protein complex that links the endoplasmic reticulum with mitochondria and may have a role in promoting exchange of calcium and phospholipids between the two organelles. The complex is also associated with actively replicating mitochondrial DNA nucleoids, and may further coordinate mitochondrial genome replication and membrane growth.
esc/e(z) complex A multimeric protein complex that can methylate lysine-27 and lysine-9 residues of histone H3. In Drosophila the core subunits of the complex include ESC, E(Z), CAF1 (NURF-55) and SU(Z)12. In mammals the core subunits of the complex include EED, EZH2, SUZ12 and RBBP4.
escrt complex An endosomal sorting complex required for transport.
escrt i complex An endosomal sorting complex required for transport. It consists of the class E vacuolar protein sorting (Vps) proteins and interacts with ubiquitinated cargoes.
escrt ii complex An endosomal sorting complex required for transport and functions downstream of ESCRT I complex. It consists of the class E vacuolar protein sorting (Vps) proteins and is required for the membrane recruitment of ESCRT III complex and binds to ubiquitinated cargoes.
escrt iii complex An endosomal sorting complex required for transport. Consists of two soluble subcomplexes of highly charged coiled-coil proteins and is required for sorting and/or concentration of multivesicular body (MVB) cargoes.
escrt-0 complex A protein complex required for the recycling of Golgi proteins, formation of lumenal membranes and sorting of ubiquitinated proteins into those membranes. This complex includes Vps1p and Hse1p in yeast and the Hrs and STAM proteins in mammals.
esterosome A vesicle filled with crystalline protein that shows sequence similarities with various esterases.
etioplast A plastid arrested in the development of chloroplasts from proplastids due to absence of light or low light conditions.
etioplast envelope The double lipid bilayer enclosing the etioplast and separating its contents from the rest of the cytoplasm; includes the intermembrane space.
etioplast membrane Either of the lipid bilayers that surround a etioplast and form the etioplast envelope.
etioplast prolamellar body A three dimensional regular lattice found in etioplasts. It is composed of a continuous system of tubules but when exposed to light the symmetrical arrangement is rapidly lost as tubules become pinched off into two dimensional sections of lattice. These for perforated sheets of membrane that move apart, extend and increase, finally establishing the typical granal and intergranal lamellae of the mature chloroplast.
euchromatin A dispersed and relatively uncompacted form of chromatin.
eukaryotic 48s preinitiation complex A protein complex composed of the small ribosomal subunit, eIF3, eIF1A, methionyl-initiatior methionine and a capped mRNA. The complex is initially positioned at the 5'-end of the capped mRNA.
eukaryotic translation elongation factor 1 complex A multisubunit nucleotide exchange complex that binds GTP and aminoacyl-tRNAs, and catalyzes their codon-dependent placement at the A-site of the ribosome. In humans, the complex is composed of four subunits, alpha, beta, delta and gamma.
eukaryotic translation initiation factor 2 complex Complex of three heterogeneous polypeptide chains, that form a ternary complex with initiator methionyl-tRNA and GTP. This ternary complex binds to free 40S subunit, which subsequently binds the 5' end of mRNA.
eukaryotic translation initiation factor 2b complex A multisubunit guanine nucleotide exchange factor which catalyzes the exchange of GDP bound to initiation factor eIF2 for GTP, generating active eIF2-GTP. In humans, it is composed of five subunits, alpha, beta, delta, gamma and epsilon.
eukaryotic translation initiation factor 3 complex A complex of several polypeptides that plays at least two important roles in protein synthesis: First, eIF3 binds to the 40S ribosome and facilitates loading of the Met-tRNA/eIF2.GTP ternary complex to form the 43S preinitiation complex. Subsequently, eIF3 apparently assists eIF4 in recruiting mRNAs to the 43S complex. The eIF3 complex contains five conserved core subunits, and may contain several additional proteins; the non-core subunits are thought to mediate association of the complex with specific sets of mRNAs.
eukaryotic translation initiation factor 4f complex The eukaryotic translation initiation factor 4F complex is composed of eIF4E, eIF4A and eIF4G; it is involved in the recognition of the mRNA cap, ATP-dependent unwinding of the 5'-terminal secondary structure and recruitment of the mRNA to the ribosome.
excinuclease repair complex Any of the protein complexes formed by the UvrABC excinuclease system, which carries out nucleotide excision repair. Three different complexes are formed by the 3 proteins as they proceed through the excision repair process. First a complex consisting of two A subunits and two B subunits bind DNA and unwind it around the damaged site. Then, the A subunits disassociate leaving behind a stable complex between B subunits and DNA. Now, subunit C binds to this B+DNA complex and causes subunit B to nick the DNA on one side of the complex while subunit C nicks the DNA on the other side of the complex. DNA polymerase I and DNA ligase can then repair the resulting gap.
excitatory synapse A synapse in which an action potential in the presynaptic cell increases the probability of an action potential occurring in the postsynaptic cell.
exine The outer layer of the pollen grain wall which is composed primarily of sporopollenin.
exocyst A protein complex peripherally associated with the plasma membrane that determines where vesicles dock and fuse. At least eight complex components are conserved between yeast and mammals.
exocytic vesicle A transport vesicle that mediates transport from an intracellular compartment to the plasma membrane, and fuses with the plasma membrane to release various cargo molecules, such as proteins or hormones, by exocytosis.
exomer complex A protein complex that forms a coat structure on vesicles involved in exocytosis of proteins from the trans-Golgi network to the cell surface; in Saccharomyces, the complex contains Chs5p, Chs6p, and Chs6p paralogues.
exon-exon junction complex A multi-subunit complex deposited by the spliceosome upstream of messenger RNA exon-exon junctions. The exon-exon junction complex provides a binding platform for factors involved in mRNA export and nonsense-mediated mRNA decay.
exoneme A dense granule-like organelle of the apical complex of merozoites, released into the parasitophorous vacuole, mediating protease-dependent rupture and parasite exit from the infected erythrocyte.
exosome (rnase complex) Complex of 3'-5' exoribonucleases.
exosporium The outermost layer of a bacterial endospore, which is loosely attached and located outside of the endospore coat. It is generally composed of protein, carbohydrate, and perhaps lipid.
external encapsulating structure A structure that lies outside the plasma membrane and surrounds the entire cell.
external encapsulating structure part Any constituent part of an external encapsulating structure, a structure that lies outside the plasma membrane and surrounds the entire cell.
external side of plasma membrane The leaflet of the plasma membrane that faces away from the cytoplasm and any proteins embedded or anchored in it or attached to its surface.
extracellular ferritin complex A ferritin complex located in the extracellular region. Extracellular ferritin complexes contain L (light) chains but few or no H (heavy) chains.
extracellular matrix A structure lying external to one or more cells, which provides structural support for cells or tissues; may be completely external to the cell (as in animals and bacteria) or be part of the cell (as in plants).
extracellular matrix part Any constituent part of the extracellular matrix, the structure lying external to one or more cells, which provides structural support for cells or tissues; may be completely external to the cell (as in animals) or be part of the cell (as often seen in plants).
extracellular membrane-bounded organelle Organized structure of distinctive morphology and function, bounded by a lipid bilayer membrane and occurring outside the cell.
extracellular non-membrane-bounded organelle Organized structure of distinctive morphology and function, not bounded by a lipid bilayer membrane and occurring outside the cell.
extracellular organelle Organized structure of distinctive morphology and function, occurring outside the cell. Includes, for example, extracellular membrane vesicles (EMVs) and the cellulosomes of anaerobic bacteria and fungi.
extracellular region The space external to the outermost structure of a cell. For cells without external protective or external encapsulating structures this refers to space outside of the plasma membrane. This term covers the host cell environment outside an intracellular parasite.
extracellular region part Any constituent part of the extracellular region, the space external to the outermost structure of a cell. For cells without external protective or external encapsulating structures this refers to space outside of the plasma membrane. This term covers constituent parts of the host cell environment outside an intracellular parasite.
extracellular space That part of a multicellular organism outside the cells proper, usually taken to be outside the plasma membranes, and occupied by fluid.
extracellular space of host The space within a host but external to the plasma membrane of host cells, e.g. within host bloodstream.
extracellular vesicle Any vesicle that is part of the extracellular region.
extracellular vesicular exosome A membrane-bounded vesicle that is released into the extracellular region by fusion of the limiting endosomal membrane of a multivesicular body with the plasma membrane.
extrachromosomal circular dna Circular DNA structures that are not part of a chromosome.
extrachromosomal dna DNA structures that are not part of a chromosome.
extrachromosomal rdna circle Circular DNA molecules encoding ribosomal RNA that are replicated independently of chromosomal replication. These molecules originate in the chromosome but are excised and circularized, often by intramolecular homologous recombination between direct tandem repeats.
extrahaustorial matrix The space between the symbiont plasma membrane and the extrahaustorial membrane of the host.
extraorganismal space The environmental space outside of an organism; this may be a host organism in the case of parasitic and symbiotic organisms.
extrinsic component of cytoplasmic side of plasma membrane The component of a plasma membrane consisting of gene products and protein complexes that are loosely bound to its cytoplasmic surface, but not integrated into the hydrophobic region.
extrinsic component of intraperoxisomal membrane The component of the intraperoxisomal membrane consisting of gene products and protein complexes that are loosely bound to one of its surfaces, but not integrated into the hydrophobic region.
extrinsic component of membrane The component of a membrane consisting of gene products and protein complexes that are loosely bound to one of its surfaces, but not integrated into the hydrophobic region.
extrinsic component of organelle membrane The component of an organelle membrane consisting of gene products and protein complexes that are loosely bound to one of its surfaces, but not integrated into the hydrophobic region.
extrinsic component of plasma membrane The component of a plasma membrane consisting of gene products and protein complexes that are loosely bound to one of its surfaces, but not integrated into the hydrophobic region.
f bouton Synaptic bouton found in the ventral horn of the spinal cord. F boutons range in diameter from 0.5 to 7 um and contain flattened or pleomorphic synaptic vesicles.
f-actin capping protein complex A heterodimer consisting of alpha and beta subunits that binds to and caps the barbed ends of actin filaments, thereby regulating the polymerization of actin monomers but not severing actin filaments.
facit collagen trimer A collagen trimer that associates with collagen fibrils and consists of collagen monomers that contain two or more relatively short triple-helical domains connected by non-triple-helical sequences.
fact complex An abundant nuclear complex, which was originally identified in mammalian systems as a factor required for transcription elongation on chromatin templates. The FACT complex has been shown to destablilize the interaction between the H2A/H2B dimer and the H3/H4 tetramer of the nucleosome, thus reorganizing the structure of the nucleosome. In this way, the FACT complex may play a role in DNA replication and other processes that traverse the chromatin, as well as in transcription elongation. FACT is composed of two proteins that are evolutionarily conserved in all eukaryotes and homologous to mammalian Spt16 and SSRP1. In metazoans, the SSRP1 homolog contains an HMG domain; however in fungi and protists, it does not. For example, in S. cerevisiae the Pob3 protein is homologous to SSRP1, but lacks the HMG chromatin binding domain. Instead, the yFACT complex of Spt16p and Pob3p, binds to nucleosomes where multiple copies of the HMG-domain containing protein Nhp6p have already bound, but Nhp6p does not form a stable complex with the Spt16p/Pob3p heterodimer.
fancm-mhf complex A protein complex contains the proteins FANCM and MHF, or their orthologs, plays an essential role in DNA remodeling, protects replication forks, and is conserved in eukaryotes.
fanconi anaemia nuclear complex A protein complex composed of the Fanconi anaemia (FA) proteins including A, C, E, G and F (FANCA-F). Functions in the activation of the downstream protein FANCD2 by monoubiquitylation, and is essential for protection against chromosome breakage.
far/sin/stripak complex A conserved protein phosphatase type 2A complex which contains a protein phosphatase type 2A, a protein phosphatase regulatory subunit, a striatin, an FHA domain protein and other subunits (at least six proteins). In fission yeast this complex negatively regulate the septation initiation network at the spindle pole body.
fascia adherens A cell-cell adherens junction that contains the transmembrane protein N-cadherin, which interacts with identical molecules from neighboring cells to form a tight mechanical intercellular link; forms a large portion of the intercalated disc, the structure at which myofibrils terminate in cardiomyocytes.
fatty acid beta-oxidation multienzyme complex A multienzyme complex possessing three kinds of enzymes that catalyze the chain reactions in the fatty acid beta-oxidation cycle, enoyl-CoA hydratase (ECH), 3-hydroxyacyl-CoA dehydrogenase (HACD), and acetyl-CoA C-acyltransferase (KACT).
fatty acid synthase complex A multienzyme complex that catalyses the synthesis of fatty acids from acetyl CoA.
fc receptor complex A protein complex composed of a subunit or subunits capable of binding the Fc portion of an immunoglobulin with additional signaling components. The complex functions as a receptor for immunoglobulin.
fc-alpha receptor i complex A protein complex composed of an Fc-alpha R alpha chain and an Fc-epsilon RI gamma chain dimer with or without additional signaling components. The complex functions primarily as an activating receptor for IgA.
fc-epsilon receptor i complex A protein complex composed of an Fc-epsilon RI alpha chain and an Fc-epsilon RI gamma chain dimer with or without an Fc-episilon RI beta chain and additional signaling components. The complex functions primarily as an activating receptor for IgE.
fc-gamma receptor i complex A protein complex composed of an Fc-gamma RI alpha chain and an Fc-epsilon RI gamma chain dimer with or without additional signaling components. The complex functions primarily as an activating receptor for IgG.
female germ cell nucleus The nucleus of the female germ cell, a reproductive cell in females.
female germline ring canal An intercellular bridge that connects the germline cells of a female cyst.
female germline ring canal inner rim A proteinaceous actin-rich layer of the insect ovarian ring canal that forms subcortically to the outer rim. The electron dense inner rim accumulates after the final mitotic division of each germline syncytia, and contains actin, a phosphotyrosine protein, and a number of cytoskeletal proteins.
female pronucleus The pronucleus originating from the ovum that is being fertilized.
ferritin complex A protein complex that binds iron and acts as a major iron storage system. Intracellular and extracellular ferritin complexes have different ratios of two types of ferritin monomer, the L (light) chain and H (heavy) chain.
fertilization envelope A structure that lies outside the plasma membrane and surrounds the egg. The fertilization envelope forms from the vitelline membrane after fertilization as a result of cortical granule release.
fhf complex A protein complex that is composed of AKTIP/FTS, FAM160A2/p107FHIP, and one or more members of the Hook family of proteins, HOOK1, HOOK2, and HOOK3. The complex is thought to promote vesicle trafficking and/or fusion, and associates with the homotypic vesicular sorting complex (the HOPS complex).
fibril Extracellular matrix material consisting of polysaccharides and protein.
fibrillar center A structure found most metazoan nucleoli, but not usually found in lower eukaryotes; surrounded by the dense fibrillar component; the zone of transcription from multiple copies of the pre-rRNA genes is in the border region between these two structures.
fibrillar collagen trimer Any triple helical collagen trimer that forms fibrils.
fibrillary inclusion Cellular inclusion consisting of circular areas filled with fine slender filaments about 10 nanometers in diameter, delimited by a wall of varying complexity (either a single continuous membrane or a tubular network consisting of a fine filamentous material giving the wall a honeycomb appearance). Fibrillary inclusions are found in the cytoplasm of giant cells of Dieters in the lateral vestibular nucleus of the rat; similar structures have been described in the ventral cochlear nucleus, spinal cord, and substantia nigra.
fibrinogen complex A highly soluble, elongated protein complex found in blood plasma and involved in clot formation. It is converted into fibrin monomer by the action of thrombin. In the mouse, fibrinogen is a hexamer, 46 nm long and 9 nm maximal diameter, containing two sets of nonidentical chains (alpha, beta, and gamma) linked together by disulfide bonds.
fibronectin-tissue transglutaminase complex A protein complex that consists of fibronectin bound to tissue transglutaminase, and is involved in cell adhesion.
filamentous actin A two-stranded helical polymer of the protein actin.
filiform apparatus A complex of cell wall invaginations in a synergid cell, similar to those in transfer cells.
filopodium Thin, stiff protrusion extended by the leading edge of a motile cell such as a crawling fibroblast or amoeba, or an axonal or dendritic growth cone, or a dendritic shaft.
filopodium tip The end of a filopodium distal to the body of the cell.
filtration diaphragm A specialized cell-cell junction found between the cells of the excretory system, which provides a barrier for filtration of blood or hemolymph.
flemming body A cell part that is the central region of the midbody characterized by a gap in alpha-tubulin staining. It is a dense structure of antiparallel microtubules from the central spindle in the middle of the intercellular bridge.
focal adhesion Small region on the surface of a cell that anchors the cell to the extracellular matrix and that forms a point of termination of actin filaments.
follicle-stimulating hormone complex A gonadotrophic glycoprotein hormone secreted, in mammals, by the anterior pituitary gland; consists of alpha and beta subunits, the latter of which confers hormonal specificity.
food vacuole Vacuole within a parasite used for digestion of the host cell cytoplasm. An example of this component is found in the Apicomplexa.
foot layer The inner layer of the ectexine.
formate dehydrogenase complex An enzyme complex that catalyzes the dehydrogenation of formate to produce carbon dioxide (CO2).
fumarate reductase complex A membrane-bound flavoenzyme complex consisting of four subunits, A, B, C, and D. A and B comprise the membrane-extrinsic catalytic domain and C (InterPro:IPR003510; InterPro:IPR004224) and D (InterPro:IPR003418) link the catalytic centers to the electron-transport chain. This family consists of the 13 kDa hydrophobic subunit D. This component may be required to anchor the catalytic components of the fumarate reductase complex to the cytoplasmic membrane. Fumarate reductase couples the reduction of fumarate to succinate to the oxidation of quinol to quinone, in a reaction opposite to that catalyzed by the related complex II of the respiratory chain (succinate dehydrogenase-(ubiquinone)).
fungal-type cell wall A rigid yet dynamic structure surrounding the plasma membrane that affords protection from stresses and contributes to cell morphogenesis, consisting of extensively cross-linked glycoproteins and carbohydrates. The glycoproteins may be modified with N- or O-linked carbohydrates, or glycosylphosphatidylinositol (GPI) anchors; the polysaccharides are primarily branched glucans, including beta-linked and alpha-linked glucans, and may also include chitin and other carbohydrate polymers, but not cellulose or pectin. Enzymes involved in cell wall biosynthesis are also found in the cell wall. Note that some forms of fungi develop a capsule outside of the cell wall under certain circumstances; this is considered a separate structure.
fusome A large intracellular spectrin-rich structure that has been found in insect germline cells and mammalian hematopoietic cells. The fusome is an elongated, branched structure, formed from the spherical spectrosome organelle.
g-protein beta/gamma-subunit complex The heterodimer formed by the beta and gamma subunits of a heterotrimeric G protein, which dissociates from the alpha subunit upon guanine nuclotide exchange.
g-protein coupled receptor complex A protein complex that contains G-protein coupled receptors.
g-protein coupled receptor dimeric complex A protein complex that contains two G-protein coupled receptors.
g-protein coupled receptor heterodimeric complex A protein complex that contains two G-protein coupled receptors (GPCRs) of different subtypes. Formation of a GPCR heterodimer may alter the functional property of the GPCR.
g-protein coupled receptor homodimeric complex A protein complex that contains two G-protein coupled receptors (GPCRs) of the same subtype. Formation of a GPCR homodimer may be important for the transport of newly formed receptors to the cell surface, and the function of the receptor.
gait complex A protein complex which mediates interferon-gamma-induced transcript-selective translation inhibition in inflammation processes. The complex binds to stem loop-containing GAIT elements in the 3'-UTR of diverse inflammatory mRNAs and suppresses their translation by blocking the recruitment of the 43S ribosomal complex to m7G cap-bound eIF4G. In humans it includes RPL13A, EPRS, SYNCRIP and GAPDH; mouse complexes lack SYNCRIP.
gamma dna polymerase complex A DNA polymerase complex consisting of a large subunit, responsible for the catalytic activities, and a small accessory subunit. Functions in the replication and repair of mitochondrial DNA.
gamma-catenin-tcf7l2 complex A protein complex that contains gamma-catenin and TCF7L2 (TCF4), binds to the TCF DNA motif within a promoter element, and is involved in the regulation of WNT target gene transcription.
gamma-delta t cell receptor complex A T cell receptor complex in which the TCR heterodimer comprises gamma and delta chains, associated with the CD3 complex; recognizes antigen directly, without a requirement for processing and presentation by an MHC protein.
gamma-secretase complex A protein complex that has aspartic-type endopeptidase activity, and contains a catalytic subunit, presenilin (PS), that is a prototypical member of the GxGD-type aspartyl peptidases. The complex also contains additional subunits, including nicastrin, APH-1, PEN-2, and a regulatory subunit, CD147. Gamma-secretase cleaves several transmembrane proteins including the cell surface receptor Notch and the beta-amyloid precursor protein.
gamma-tubulin complex A multiprotein complex composed of gamma-tubulin and other non-tubulin proteins. Gamma-tubulin complexes are localized to microtubule organizing centers, and play an important role in the nucleation of microtubules. The number and complexity of non-tubulin proteins associated with these complexes varies between species.
gamma-tubulin large complex A complex of gamma tubulin and associated proteins thought to be formed by multimerization of gamma-tubulin small complexes. An example of this structure is found in Schizosaccharomyces pombe.
gamma-tubulin ring complex A multiprotein complex composed of gamma-tubulin and other non-tubulin proteins that forms a flexible open ring structure thought to be the unit of nucleation at the minus end of a microtubule.
gamma-tubulin small complex A complex usually comprising two gamma-tubulin molecules and two conserved non-tubulin proteins. Some gamma-tubulin small complexes are thought to be the repeating unit making up the core of the gamma-tubulin ring complex.
gap junction A cell-cell junction that is composed of an array of small channels that permit small molecules to pass from one cell to another. At gap junctions, the membranes of two adjacent cells are separated by a uniform narrow gap of about 2-4 nm that is spanned by channel-forming proteins called connexins, which form hexagonal tubes called connexons.
garp complex A quatrefoil tethering complex required for retrograde traffic from the early endosome back to the late Golgi and biogenesis of cytoplasmic vesicles.
gas vesicle A hollow structure made of protein, which usually has the form of a cylindrical tube closed by conical end caps. By regulating their relative gas vesicle content aquatic microbes are able to perform vertical migrations.
gas vesicle shell The proteinaceous structure surrounding a gas vesicle.
gemin3-gemin4-gemin5 complex A protein complex that contains Gemin3 (DDX20), Gemin4, and Gemin5, and can bind to snRNAs; may be an intermediate in SMN complex assembly.
gemin6-gemin7-unrip complex A protein complex that contains Gemin6, Gemin7, and unrip (STRAP), and can bind to snRNAs; may play a role in snRNP assembly.
gemmule Spine-like process found on some neurons, e.g., periglomerular cells of olfactory cortex.
generative cell nucleus The nucleus of the generative cell, a cell contained within the pollen grain that will divide to produce two haploid sperm cells.
germ cell nucleus The nucleus of a germ cell, a reproductive cell in multicellular organisms.
germ plasm Differentiated cytoplasm associated with a pole of an oocyte, egg or early embryo that will be inherited by the cells that will give rise to the germ line.
germ tube The slender tubular outgrowth first produced by most spores in germination.
germinal vesicle The enlarged, fluid filled nucleus of a primary oocyte, the development of which is suspended in prophase I of the first meiotic division between embryohood and sexual maturity.
germination pore A small pore in the outer wall of a mycelial spore through which the germ tube exits upon germination. It can be apical or eccentric in its location.
germline ring canal Germline specific intercellular bridge. During cyst formation in insects, ring canals interconnect the cells of the cyst, facilitating the passage of cytoplasmic components between cells.
gerontoplast A plastid found in senescing, formerly green tissues that is derived from a chloroplast that undergoes an organized developmental program of senescence.
get complex A multisubunit complex involved in ER/Golgi trafficking (Golgi to ER Traffic). In yeast, includes Get1p, Get2p and Get3p proteins.
giant axon Extremely large, unmyelinated axon found in invertebrates. Has high conduction speeds and is usually involved in panic or escape responses.
gid complex A protein complex with ubiquitin ligase activity that is involved in proteasomal degradation of fructose-1,6-bisphosphatase (FBPase) and phosphoenolpyruvate carboxykinase during the transition from gluconeogenic to glycolytic growth conditions. In S. cerevisiae, the GID (Glucose Induced degradation Deficient) complex consists of Vid30p, Rmd5p, Vid24p, Vid28p, Gid7p, Gid8p, and Fyv10p.
gins complex A heterotetrameric protein complex that associates with replication origins, where it is required for the initiation of DNA replication, and with replication forks.
glial cell projection A prolongation or process extending from a glial cell.
glial cytoplasmic inclusion Non-membrane-bound cytoplasmic inclusions composed of 10-40 nm granule-coated fibrils. These inclusions have an abnormal accumulation of alpha-synuclein protein and are found in association with multiple system atrophy.
glial filament An intermediate filament composed of glial fibrillary acidic protein (GFAP) and found in astrocytes.
glucosidase complex A protein complex which is capable of glucosidase activity.
glucosidase ii complex A heterodimeric complex that catalyzes the trimming of glucose residues from N-linked core glycans on newly synthesized glycoproteins.
glutamyl-trna(gln) amidotransferase complex A protein complex that possesses glutamyl-tRNA(Gln) amidotransferase activity, and therefore creates Gln-tRNA by amidating Glu-tRNA; usually composed of 3 subunits: A, B, and C. Note that the C subunit may not be required in all organisms.
glycine cleavage complex A protein complex that catalyzes the reversible oxidation of glycine. In E. coli, it has four components: dihydrolipoamide dehydrogenase, glycine dehydrogenase (decarboxylating), lipoyl-GcvH-protein and aminomethyltransferase, also known as L, P, H, and T.
glycine reductase complex Complex that possesses glycine reductase activity; usually comprises three subunits, of which two are selenoproteins; the subunits are typically designated selenoprotein A, selenoprotein B and protein C.
glycine-gated chloride channel complex A protein complex that forms a transmembrane channel through which chloride ions may pass in response to glycine binding to the channel complex or one of its constituent parts.
glycocalyx A viscous, carbohydrate rich layer at the outermost periphery of a cell.
glycogen granule Cytoplasmic bead-like structures of animal cells, visible by electron microscope. Each granule is a functional unit with the biosynthesis and catabolism of glycogen being catalyzed by enzymes bound to the granule surface.
glycoprotein network An extracellular matrix part that consists of cross-linked glycoproteins.
glycosome A membrane-bounded organelle found in organisms from the order Kinetoplastida that houses the enzymes of glycolysis.
glycosome lumen The volume enclosed by the membrane of a glycosome.
glycosome membrane The lipid bilayer surrounding a glycosome.
glycosylphosphatidylinositol-n-acetylglucosaminyltransferase (gpi-gnt) complex An enzyme complex that catalyzes the transfer of GlcNAc from UDP-GlcNAc to an acceptor phosphatidylinositol, the first step in the production of GPI anchors for cell surface proteins. The complex contains PIG-A, PIG-C, PIG-H, PIG-Q, PIG-P, and DPM2 in human, and Eri1p, Gpi1p, Gpi2p, Gpi15p, Gpi19p, and Spt14p in budding yeast.
glyoxysomal lumen The volume enclosed by the membranes of a glyoxysome.
glyoxysomal membrane The lipid bilayer surrounding a glyoxysome.
glyoxysome A specialized form of peroxisome that contains the enzymes of the glyoxylate pathway. The glyoxysome is found in some plant cells, notably the cells of germinating seeds.
golgi apparatus A compound membranous cytoplasmic organelle of eukaryotic cells, consisting of flattened, ribosome-free vesicles arranged in a more or less regular stack. The Golgi apparatus differs from the endoplasmic reticulum in often having slightly thicker membranes, appearing in sections as a characteristic shallow semicircle so that the convex side (cis or entry face) abuts the endoplasmic reticulum, secretory vesicles emerging from the concave side (trans or exit face). In vertebrate cells there is usually one such organelle, while in invertebrates and plants, where they are known usually as dictyosomes, there may be several scattered in the cytoplasm. The Golgi apparatus processes proteins produced on the ribosomes of the rough endoplasmic reticulum; such processing includes modification of the core oligosaccharides of glycoproteins, and the sorting and packaging of proteins for transport to a variety of cellular locations. Three different regions of the Golgi are now recognized both in terms of structure and function: cis, in the vicinity of the cis face, trans, in the vicinity of the trans face, and medial, lying between the cis and trans regions.
golgi apparatus part Any constituent part of the Golgi apparatus, a compound membranous cytoplasmic organelle of eukaryotic cells, consisting of flattened, ribosome-free vesicles arranged in a more or less regular stack.
golgi cisterna Any of the thin, flattened membrane-bounded compartments that form the central portion of the Golgi complex.
golgi cisterna membrane The lipid bilayer surrounding any of the thin, flattened compartments that form the central portion of the Golgi complex.
golgi lumen The volume enclosed by the membranes of any cisterna or subcompartment of the Golgi apparatus, including the cis- and trans-Golgi networks.
golgi membrane The lipid bilayer surrounding any of the compartments of the Golgi apparatus.
golgi stack The set of thin, flattened membrane-bounded compartments, called cisternae, that form the central portion of the Golgi complex. The stack usually comprises cis, medial, and trans cisternae; the cis- and trans-Golgi networks are not considered part of the stack.
golgi trans cisterna The Golgi cisterna farthest from the endoplasmic reticulum; the final processing compartment through which proteins pass before exiting the Golgi apparatus; the compartment in which N-linked protein glycosylation is completed.
golgi transport complex A complex of proteins that, in vitro, stimulates intra-Golgi transport; a 13S complex, about 800 kDa in size and consists of at least five polypeptides. In yeast, this complex is called the Sec34/35 complex and is composed of eight subunits (Sec34p, Sec35p, Dor1p, Cod1p, Cod2p, Cod3p, Cod4p, and Cod5p).
golgi-associated vesicle Any vesicle associated with the Golgi complex and involved in mediating transport within the Golgi or between the Golgi and other parts of the cell.
golgi-associated vesicle membrane The lipid bilayer surrounding a vesicle associated with the Golgi apparatus.
gpi-anchor transamidase complex An enzyme complex which in humans and yeast consists of at least five proteins; for example, the complex contains GAA1, GPI8, PIG-S, PIG-U, and PIG-T in human, and Gaa1p, Gab1p, Gpi8p, Gpi16p, and Gpi17p in yeast. Catalyzes the posttranslational attachment of the carboxyl-terminus of a precursor protein to a GPI-anchor.
granular component A structure found in the nucleolus, which contains nearly completed preribosomal particles destined for the cytoplasm.
granular vesicle A cytoplasmic membrane-bounded vesicle of varying size, but usually larger than 45 nm, with an electron dense granular core, found in noradrenergic and peptidergic cells.
granulocyte macrophage colony-stimulating factor receptor complex The heterodimeric receptor for granulocyte macrophage colony-stimulating factor.
granum Distinct stack of lamellae seen within chloroplasts. Grana contain the pigments, electron transfer compounds, and enzymes essential to the light-dependent reactions of photosynthesis.
grb2-egfr complex A protein complex that contains the epidermal growth factor receptor (EGFR) and Grb2, and is involved in linking EGFR activation to the p21-Ras pathway.
grb2-shc complex A protein complex that contains Grb2 and the adaptor protein Shc, and is involved in linking epidermal growth factor receptor (EGFR) activation to the p21-Ras pathway.
grb2-shp-2 complex A protein complex that contains the receptor adaptor proteins Grb2 and SHP-2, and is involved signaling via the PDGFR signaling pathway.
grb2-sos complex A protein complex that contains Grb2 and the guanine nucleotide exchange factor Sos (or an ortholog thereof, such as mSos1), and is involved in linking EGFR activation to the p21-Ras pathway.
growing cell tip The region at either end of the longest axis of a cylindrical or elongated cell, where polarized growth occurs.
growth cone The migrating motile tip of a growing nerve cell axon or dendrite.
growth cone membrane The portion of the plasma membrane surrounding a growth cone.
growth factor complex A protein complex that has growth factor activity.
growth hormone receptor complex A receptor complex that consists of two identical subunits and binds growth hormone.
guanyl-nucleotide exchange factor complex A protein complex that stimulates the exchange of guanyl nucleotides associated with a GTPase.
guanylate cyclase complex, soluble Complex that possesses guanylate cyclase activity and is not bound to a membrane.
h zone A relatively pale zone traversing the center of the A band of a sarcomere, visible in relaxed muscle fibers; consists of the central portion of thick (myosin) filaments that are not overlapped by thin (actin) filaments.
h3 histone acetyltransferase complex A multisubunit complex that catalyzes the acetylation of histone H3.
h4 histone acetyltransferase complex A protein complex which is capable of H4 histone acetyltransferase activity.
h4/h2a histone acetyltransferase complex A multisubunit complex that catalyzes the acetylation of histones H4 and H2A.
haptoglobin-hemoglobin complex A protein complex formed by the stable binding of a haptoglobin to hemoglobin.
haus complex A protein complex that localizes to interphase centrosomes and to mitotic spindle tubules and regulates mitotic spindle assembly and centrosome integrity; in human, the complex consists of eight subunits, some of which are homologous to subunits of the Drosophila Augmin complex.
haustorium A projection from a cell or tissue that penetrates the host's cell wall and invaginates the host cell membrane.
hda1 complex A tetrameric histone deacetylase complex that contains a Class II deacetylase catalytic subunit. In S. cerevisiae it is composed of two Hda1p subunits along with Hda2p and Hda3p.
heavy chain immunoglobulin complex A protein complex composed of two identical immunoglobulin heavy chains of the IgNAR isotype held together by disulfide bonds and lacking immunoglobulin light chains.
hedgehog signaling complex A multiprotein complex that binds microtubules in a Hedgehog-dependent manner, and is required for signal transduction by members of the Hedgehog family of proteins. The core components of the complex are the serine/threonine protein kinase Fused, the kinesin motor protein Costal2 (Cos2), and a zinc finger transcription factor (Gli family members in humans, and Cubitus interruptus (Ci) in Drosophila).
hemidesmosome A cell-substrate junction that forms a point of contact between the basal surface of epithelial cells and the basal lamina. Morphologically resembles desmosomes; attached to intermediate filaments.
hemidesmosome associated protein complex Any protein complex that is part of or has some part in a hemidesmosome.
hemoglobin complex An iron-containing, oxygen carrying complex. In vertebrates it is made up of two pairs of associated globin polypeptide chains, each chain carrying a noncovalently bound heme prosthetic group.
heterochromatin A compact and highly condensed form of chromatin.
heterotrimeric g-protein complex Any of a family of heterotrimeric GTP-binding and hydrolyzing proteins; they belong to a superfamily of GTPases that includes monomeric proteins such as EF-Tu and RAS. Heterotrimeric G-proteins consist of three subunits; the alpha subunit contains the guanine nucleotide binding site and possesses GTPase activity; the beta and gamma subunits are tightly associated and function as a beta-gamma heterodimer; extrinsic plasma membrane proteins (cytoplasmic face) that function as a complex to transduce signals from G-protein coupled receptors to an effector protein.
hics complex A multisubunit complex involved in cytokinesis. In the yeast Saccharomyces cerevisiae this complex consists of Sho1p, Hof1p, Inn1p and Cyk3p proteins.
high-affinity iron permease complex A protein complex composed of a multicopper ferroxidase that oxidizes Fe(II) to Fe(III), and a ferric iron permease that transports the produced Fe(III) into the cell. In high-affinity transport the transporter is able to bind the solute even if it is only present at very low concentrations.
high-density lipoprotein particle A lipoprotein particle with a high density (typically 1.063-1.21 g/ml) and a diameter of 5-10 nm that contains APOAs and may contain APOCs and APOE; found in blood and carries lipids from body tissues to the liver as part of the reverse cholesterol transport process.
hir complex A protein complex proposed to be involved in replication-independent nucleosome assembly, by promoting histone deposition onto DNA. For example, in Saccharomyces, the complex contains Hir1p, Hir2p, Hir3p, and Hpc2p.
histone acetyltransferase complex A protein complex that possesses histone acetyltransferase activity.
histone deacetylase complex A protein complex that possesses histone deacetylase activity.
histone locus body A nuclear body associated with the histone gene locus that is thought to contain all of the factors necessary for histone mRNA transcription and pre-mRNA processing. In Drosophila, U7 snRNP is located in the histone locus body rather than the distinct Cajal body.
histone methyltransferase complex A multimeric complex that is able to catalyze the addition of methyl groups to histone proteins.
histone pre-mrna 3'end processing complex A ribonucleoprotein that binds to specific sites in, and is required for cleavage of, the 3'-end of histone pre-mRNAs. The complex contains the U7 snRNP and additional proteins, including the stem-loop binding protein (SLBP) and the exonuclease 3'hExo/Eri-1.
holliday junction resolvase complex A protein complex that mediates the conversion of a Holliday junction into two separate duplex DNA molecules; the complex includes a single- or multisubunit helicase that catalyzes the extension of heteroduplex DNA by branch migration and a nuclease that resolves the junction by nucleolytic cleavage.
homodimeric serine palmitoyltransferase complex A homodimeric complex which transfers a palmitoyl group onto serine, forming 3-dehydro-D-sphinganine.
hops complex A multimeric protein complex that associates with the vacuolar membrane, late endosomal (multivesicular body) and lysosomal membranes. HOPS is a tethering complex involved in vesicle fusion.
horsetail-astral microtubule array An array of astral microtubules that emanates from the spindle pole body during meiosis and facilitates horsetail nuclear movement.
host Any organism in which another organism, especially a parasite or symbiont, spends part or all of its life cycle and from which it obtains nourishment and/or protection.
host cell nuclear part Any constituent part of a host cell's nucleus, a membrane-bounded organelle of eukaryotic cells in which chromosomes are housed and replicated. The host is the larger of the organisms involved in a symbiotic interaction.
host cell part Any constituent part of a host cell. The host is defined as the larger of the organisms involved in a symbiotic interaction.
host intracellular part Any constituent part of the living contents of a host cell; the matter contained within (but not including) the plasma membrane, usually taken to exclude large vacuoles and masses of secretory or ingested material. In eukaryotes it includes the nucleus and cytoplasm. The host is defined as the larger of the organisms involved in a symbiotic interaction.
hrd1p ubiquitin ligase complex A multiprotein complex that recognizes and ubiquitinates proteins with misfolded luminal and membrane domains during ER-associated protein degradation (ERAD). In S. cerevisiae, this complex contains the ubiquitin ligase Hrd1p.
hsluv protease complex A protein complex that possesses ATP-dependent protease activity; consists of an ATPase large subunit with homology to other ClpX family ATPases and a peptidase small subunit related to the proteasomal beta-subunits of eukaryotes. In the E. coli complex, a double ring-shaped homohexamer of HslV is capped on each side by a ring-shaped HslU homohexamer.
hulc complex A ubiquitin-conjugating enzyme complex that contains two RING finger proteins, which have ubiquitin ligase activity, in addition to a protein with ubiquitin-conjugating enzyme activity; catalyzes the ubiquitination of histone H2B at lysine 119 (or the equivalent residue). In Schizosaccharomyces the subunits are Rhp1, Brl2/Rfp1 and Brl1/Rfp2.
hyaline inclusion A glass-like, pale intracellular inclusion.
hyaline layer A multilayered extraembryonic matrix that functions as a substrate for cell adhesion through early development. It is thought to protect and lubricate the embryo, stabilize the blastomeres during morphogenesis, and regulate nutrient intake. The major constituent of the hyaline layer is the protein hyalin. This matrix has been found in echinoderms.
hyaluranon cable A cable structure, surrounding some cell types (e.g. proximal or bronchial tubular epithelial cells), and composed of hyaluranon (HA), a ubiquitous connective tissue glycosaminoglycan.
hydrogenosomal membrane The lipid bilayer surrounding a hydrogenosome.
hydrogenosome A spherical, membrane-bounded organelle found in some anaerobic protozoa, which participates in ATP and molecular hydrogen formation.
hyphal cell wall The cell wall surrounding a fungal hypha.
hyphal tip The end, or tip, of a fungal hypha, where polarized growth occurs during hyphal elongation.
hypolemmal cisterna Specialized part of the smooth endoplasmic reticulum that closely underlies the plasma membrane, usually within 60 nm or closer.
i band A region of a sarcomere that appears as a light band on each side of the Z disc, comprising a region of the sarcomere where thin (actin) filaments are not overlapped by thick (myosin) filaments; contains actin, troponin, and tropomyosin; each sarcomere includes half of an I band at each end.
i-aaa complex Protease complex of the mitochondrial inner membrane whose catalytic residues lie on the intermembrane space side of the inner membrane; involved in mitochondrial protein turnover. Contains a subunit belonging to the AAA family of ATP-dependent metalloproteases.
i-kappab/nf-kappab complex A protein complex containing an inhibitory-kappaB (I-kappaB/IKB) protein and one or more copies of an NF-kappaB protein. In the resting state, NF-kappaB dimers are bound to I-kappaB proteins, sequestering NF-kappaB in the cytoplasm.
icosahedral viral capsid The protein coat that surrounds the infective nucleic acid in some virus particles; the subunits are arranged to form an icosahedron, a solid with 20 faces and 12 vertices. Icosahedral capsids have 12 pentamers plus 10(T-1) hexamers, where T is the triangulation number. Tobacco satellite necrosis virus has such a capsid structure.
iga b cell receptor complex An IgA immunoglobulin complex that is present in the plasma membrane of B cells and is composed of two identical immunoglobulin heavy chains of an IgA isotype and two identical immunoglobulin light chains and a signaling subunit, a heterodimer of the Ig-alpha and Ig-beta proteins.
iga immunoglobulin complex A protein complex composed of two identical immunoglobulin heavy chains of the IgA isotype and two identical immunoglobulin light chains, held together by disulfide bonds, and sometimes complexed with J chain or J chain and secretory component. An IgA immunoglobulin complex may be embedded in the plasma membrane or present in the extracellular space, in mucosal areas or other tissues, or circulating in the blood or lymph.
iga immunoglobulin complex, circulating A protein complex composed of two identical immunoglobulin heavy chains of an IgA isotype and two identical immunoglobulin light chains, held together by disulfide bonds, sometimes complexed with J chain or J chain and secretory component, and present in the extracellular space, in mucosal areas or other tissues, or circulating in the blood or lymph.
igd b cell receptor complex An IgD immunoglobulin complex that is present in the plasma membrane of B cells and is composed of two identical immunoglobulin heavy chains of the IgD isotype and two identical immunoglobulin light chains and a signaling subunit, a heterodimer of the Ig-alpha and Ig-beta proteins.
igd immunoglobulin complex A protein complex composed of two identical immunoglobulin heavy chains of the IgD isotype and two identical immunoglobulin light chains, held together by disulfide bonds. An IgD immunoglobulin complex may be embedded in the plasma membrane or present in the extracellular space, in mucosal areas or other tissues, or circulating in the blood or lymph.
ige b cell receptor complex An IgE immunoglobulin complex that is present in the plasma membrane of B cells and is composed of two identical immunoglobulin heavy chains of the IgE isotype and two identical immunoglobulin light chains and a signaling subunit, a heterodimer of the Ig-alpha and Ig-beta proteins.
ige immunoglobulin complex A protein complex composed of two identical immunoglobulin heavy chains of the IgE isotype and two identical immunoglobulin light chains, held together by disulfide bonds. An IgE immunoglobulin complex may be embedded in the plasma membrane or present in the extracellular space, in mucosal areas or other tissues, or circulating in the blood or lymph.
ige immunoglobulin complex, circulating A protein complex composed of two identical immunoglobulin heavy chains of the IgE isotype and two identical immunoglobulin light chains, held together by disulfide bonds, and present in the extracellular space, in mucosal areas or other tissues, or circulating in the blood or lymph.
igg b cell receptor complex An IgG immunoglobulin complex that is present in the plasma membrane of B cells and is composed of two identical immunoglobulin heavy chains of an IgG isotype and two identical immunoglobulin light chains and a signaling subunit, a heterodimer of the Ig-alpha and Ig-beta proteins.
igg immunoglobulin complex A protein complex composed of two identical immunoglobulin heavy chains of an IgG isotype and two identical immunoglobulin light chains, held together by disulfide bonds. An IgG immunoglobulin complex may be embedded in the plasma membrane or present in the extracellular space, in mucosal areas or other tissues, or circulating in the blood or lymph.
igm b cell receptor complex An IgM immunoglobulin complex that is present in the plasma membrane of B cells and is composed of two identical immunoglobulin heavy chains of the IgM isotype and two identical immunoglobulin light chains and a signaling subunit, a heterodimer of the Ig-alpha and Ig-beta proteins.
igm immunoglobulin complex A protein complex composed of two identical immunoglobulin heavy chains of the IgM isotype and two identical immunoglobulin light chains, held together by disulfide bonds, and in its circulating form complexed with J chain in polymeric forms. An IgM immunoglobulin complex may be embedded in the plasma membrane or present in the extracellular space, in mucosal areas or other tissues, or circulating in the blood or lymph.
igy immunoglobulin complex A protein complex composed of two identical immunoglobulin heavy chains of the IgY isotype and two identical immunoglobulin light chains, held together by disulfide bonds. An IgY immunoglobulin complex may be embedded in the plasma membrane or present in the extracellular space, in mucosal areas or other tissues, or circulating in the blood or lymph.
ikappab kinase complex A trimeric protein complex that phosphorylates inhibitory-kappaB (I-kappaB) proteins. The complex is composed of two kinase subunits (alpha and beta) and a regulatory gamma subunit (also called NEMO). In a resting state, NF-kappaB dimers are bound to inhibitory IKB proteins, sequestering NF-kappaB in the cytoplasm. Phosphorylation of I-kappaB targets I-kappaB for ubiquitination and proteasomal degradation, thus releasing the NF-kappaB dimers, which can translocate to the nucleus to bind DNA and regulate transcription.
ikkalpha-ikkalpha complex A homodimeric protein complex containing two IkappaB kinase (IKK) alpha subunits.
immunoglobulin complex A protein complex that in its canonical form is composed of two identical immunoglobulin heavy chains and two identical immunoglobulin light chains, held together by disulfide bonds and sometimes complexed with additional proteins. An immunoglobulin complex may be embedded in the plasma membrane or present in the extracellular space, in mucosal areas or other tissues, or circulating in the blood or lymph.
immunoglobulin complex, circulating An immunoglobulin complex that is secreted into extracellular space and found in mucosal areas or other tissues or circulating in the blood or lymph. In its canonical form, a circulating immunoglobulin complex is composed of two identical heavy chains and two identical light chains, held together by disulfide bonds. Some forms of are polymers of the basic structure and contain additional components such as J-chain and the secretory component.
immunological synapse An area of close contact between a lymphocyte (T-, B-, or natural killer cell) and a target cell formed through the clustering of particular signaling and adhesion molecules and their associated membrane rafts on both the lymphocyte and the target cell and facilitating activation of the lymphocyte, transfer of membrane from the target cell to the lymphocyte, and in some situations killing of the target cell through release of secretory granules and/or death-pathway ligand-receptor interaction.
inad signaling complex A complex of proteins that are involved in phototransduction and attached to the transient receptor potential (TRP) channel. The protein connections are mediated through inaD.
inclusion body A discrete intracellular part formed of aggregated molecules such as proteins or other biopolymers.
inhibin a complex Heterodimeric hormone composed of an inhibin alpha subunit complexed with an inhibin beta-A subunit.
inhibin b complex Heterodimeric hormone composed of an inhibin alpha subunit complexed with an inhibin beta-B subunit.
inhibin complex Heterodimeric hormone composed of an inhibin alpha subunit complexed with either an inhibin beta-A subunit, to form inhibin A, or an inhibin beta-B subunit, to form inhibin B.
inhibitory synapse A synapse in which an action potential in the presynaptic cell reduces the probability of an action potential occurring in the postsynaptic cell.
inner acrosomal membrane The acrosomal membrane region that underlies the acrosomal vesicle and is located toward the sperm nucleus. This region is responsible for molecular interactions allowing the sperm to penetrate the zona pellucida and fuses with the egg plasma membrane.
inner dynein arm Inner arm structure present on the outer doublet microtubules of ciliary and flagellar axonemes. The structure of inner dynein arms is complex and may vary within the axoneme. Inner and outer dynein arms have different functions in the generation of microtubule-based motility.
inner membrane complex A membrane structure formed of two closely aligned lipid bilayers that lie beneath the plasma membrane and form part of the pellicle surrounding an apicomplexan parasite cell.
inner mucus layer The inner of two mucus layers secreted by epithelial cells in the colon; the inner mucus layer is firmly attached to the epithelium, is densely packed with a compact stratified appearance and is devoid of bacteria.
ino80 complex A multisubunit protein complex that contains the Ino80p ATPase; exhibits chromatin remodeling activity and 3' to 5' DNA helicase activity.
ino80-type complex A chromatin remodeling protein complex initially purified from S. cerevisiae and containing more than 10 subunits, including the SWR1-related complexes. INO80 (inositol requiring 80)-type complexes have diverse functions, including promoting transcriptional activation and DNA repair.
insulin receptor complex A disulfide-bonded, heterotetrameric receptor complex. The alpha chains are entirely extracellular, while each beta chain has one transmembrane domain. The ligand binds to the alpha subunit extracellular domain and the kinase is associated with the beta subunit intracellular domain.
insulin-like growth factor binary complex A complex of two proteins, which in animals is 50kDa and consists of the insulin-like growth factor (IGF) and one of the insulin-like growth factor binding protein-1 (IGFBP-1), -2 (IGFBP-2), -4 (IGFBP-4) and -6 (IGFBP-6). The complex plays a role in growth and development.
insulin-like growth factor binding protein complex A complex of proteins which includes the insulin-like growth factor (IGF) and a number of IGF-binding proteins. The complex plays a role in growth and development.
insulin-like growth factor ternary complex A complex of three proteins, which in animals is approximately 150kDa and consists of the insulin-like growth factor (IGF), the insulin-like growth factor binding protein-3 (IGFBP-3), or -5 (IGFBP-5) and an acid-labile subunit (ALS). The complex plays a role in growth and development.
insulin-responsive compartment A small membrane-bounded vesicle that releases its contents by exocytosis in response to insulin stimulation; the contents are enriched in GLUT4, IRAP and VAMP2.
integral component of endoplasmic reticulum membrane The component of the endoplasmic reticulum membrane consisting of gene products and protein complexes that have some part that penetrates at least one leaflet of the membrane bilayer. This component includes gene products that are buried in the bilayer with no exposure outside the bilayer.
integral component of golgi membrane The component of the Golgi membrane consisting of gene products and protein complexes that have some part that penetrates at least one leaflet of the membrane bilayer. This component includes gene products that are buried in the bilayer with no exposure outside the bilayer.
integral component of membrane The component of a membrane consisting of gene products and protein complexes that have some part that penetrates at least one leaflet of the membrane bilayer. This component includes gene products that are buried in the bilayer with no exposure outside the bilayer.
integral component of mitochondrial inner membrane The component of the mitochondrial inner membrane consisting of the gene products that have some part that penetrates at least one leaflet of the membrane bilayer. This component includes gene products that are buried in the bilayer with no exposure outside the bilayer.
integral component of mitochondrial membrane The component of the mitochondrial membrane consisting of the gene products that have some part that penetrates at least one leaflet of the membrane bilayer. This component includes gene products that are buried in the bilayer with no exposure outside the bilayer.
integral component of organelle membrane The component of the organelle membrane consisting of the gene products that have some part that penetrates at least one leaflet of the membrane bilayer. This component includes gene products that are buried in the bilayer with no exposure outside the bilayer.
integral component of plasma membrane The component of the plasma membrane consisting of gene products and protein complexes that have some part that penetrates at least one leaflet of the membrane bilayer. This component includes gene products that are buried in the bilayer with no exposure outside the bilayer.
integrator complex A protein complex that stably associates with the C-terminus of RNA polymerase II and mediates 3'-end processing of small nuclear RNAs generated by RNA polymerase II.
integrin alpha1-beta1 complex An integrin complex that comprises one alpha1 subunit and one beta1 subunit.
integrin alpha10-beta1 complex An integrin complex that comprises one alpha10 subunit and one beta1 subunit.
integrin alpha11-beta1 complex An integrin complex that comprises one alpha11 subunit and one beta1 subunit.
integrin alpha2-beta1 complex An integrin complex that comprises one alpha2 subunit and one beta1 subunit.
integrin alpha3-beta1 complex An integrin complex that comprises one alpha3 subunit and one beta1 subunit.
integrin alpha4-beta1 complex An integrin complex that comprises one alpha4 subunit and one beta1 subunit.
integrin alpha4-beta7 complex An integrin complex that comprises one alpha4 subunit and one beta7 subunit.
integrin alpha5-beta1 complex An integrin complex that comprises one alpha5 subunit and one beta1 subunit.
integrin alpha6-beta1 complex An integrin complex that comprises one alpha6 subunit and one beta1 subunit.
integrin alpha6-beta4 complex An integrin complex that comprises one alpha6 subunit and one beta1 subunit.
integrin alpha7-beta1 complex An integrin complex that comprises one alpha7 subunit and one beta1 subunit.
integrin alpha8-beta1 complex An integrin complex that comprises one alpha8 subunit and one beta1 subunit.
integrin alpha9-beta1 complex An integrin complex that comprises one alpha9 subunit and one beta1 subunit.
integrin alphad-beta2 complex An integrin complex that comprises one alphaD subunit and one beta2 subunit.
integrin alphae-beta7 complex An integrin complex that comprises one alphaE subunit and one beta7 subunit.
integrin alphaiib-beta3 complex An integrin complex that comprises one alphaIIb subunit and one beta3 subunit.
integrin alphal-beta2 complex An integrin complex that comprises one alphaL subunit and one beta2 subunit.
integrin alpham-beta2 complex An integrin complex that comprises one alphaM subunit and one beta2 subunit.
integrin alphav-beta1 complex An integrin complex that comprises one alphav subunit and one beta1 subunit.
integrin alphav-beta3 complex An integrin complex that comprises one alphav subunit and one beta3 subunit.
integrin alphav-beta5 complex An integrin complex that comprises one alphav subunit and one beta5 subunit.
integrin alphav-beta6 complex An integrin complex that comprises one alphav subunit and one beta6 subunit.
integrin alphav-beta8 complex An integrin complex that comprises one alphav subunit and one beta8 subunit.
integrin alphax-beta2 complex An integrin complex that comprises one alphaX subunit and one beta2 subunit.
integrin complex A protein complex that is composed of one alpha subunit and one beta subunit, both of which are members of the integrin superfamily of cell adhesion receptors; the complex spans the plasma membrane and binds to extracellular matrix ligands, cell-surface ligands, and soluble ligands.
intercalary heterochromatin Any of the regions of heterochromatin that form a reproducible set of dense bands scattered along the euchromatic arms in polytene chromosomes.
intercalated disc A complex cell-cell junction at which myofibrils terminate in cardiomyocytes; mediates mechanical and electrochemical integration between individual cardiomyocytes. The intercalated disc contains regions of tight mechanical attachment (fasciae adherentes and desmosomes) and electrical coupling (gap junctions) between adjacent cells.
intercellular bridge A direct connection between the cytoplasm of two cells that is formed following the completion of cleavage furrow ingression during cell division. They are usually present only briefly prior to completion of cytokinesis. However, in some cases, such as the bridges between germ cells during their development, they become stabilised.
intercellular canaliculus An extremely narrow tubular channel located between adjacent cells. An instance of this is the secretory canaliculi occurring between adjacent parietal cells in the gastric mucosa of vertebrates.
interchromatin granule A class of nuclear body measuring 20-25 nm in diameter and distributed throughout the interchromatin space, linked together by thin fibrils. They are believed to be storage centers for various snRNAs, snRNPs, serine/arginine-rich proteins and RNA polymerase II. A typical mammalian cell contains 25-50 clusters of interchromatin granules. Interchromatin granule clusters do not contain the heterogeneous nuclear RNA-binding proteins (hnRNPs).
interferon regulatory factor 3 complex An interferon regulatory factor complex that consists of a homodimer of interferon regulatory factor 3.
interferon regulatory factor 3-interferon regulatory factor 7 complex An interferon regulatory factor complex that consists of a heterodimer of interferon regulatory factor 3 and interferon regulatory factor 7.
interferon regulatory factor complex A protein complex that consists of two interferon regulatory proteins (IRFs); may be homodimeric or heterodimeric. The activation of a latent closed conformation of IRF in the cytoplasm is triggered by phosphorylation of Ser/Thr residues in a C-terminal region. Phosphorylation stimulates the C-terminal autoinhibitory domain to attain a highly extended conformation triggering dimerization through extensive contacts to a second subunit.
interleukin-1 receptor complex A protein complex that binds interleukin-1; comprises an alpha and a beta subunit.
interleukin-12 complex A protein complex that is composed of an interleukin-12 alpha (p35, product of the IL12A gene) and an interleukin-12 beta subunit (p40, product of the IL12B gene) and is secreted into the extracellular space.
interleukin-12 receptor complex A protein complex that binds interleukin-12; comprises a beta1 and a beta2 subunit.
interleukin-13 receptor complex A protein complex that binds interleukin-13; consists of two chains, interleukin-13 receptor alpha1 chain and interleukin-4 receptor alpha chain.
interleukin-18 receptor complex A protein complex that binds interleukin-18; comprises an alpha and a beta subunit.
interleukin-2 receptor complex A protein complex that binds interleukin-2; comprises alpha, beta, and gamma subunits.
interleukin-23 complex A protein complex that is composed of an interleukin-23 alpha (p19, product of the IL23A gene) and an interleukin-12 beta (p40, product of the IL12B gene) subunit and is secreted into the extracellular space.
interleukin-23 receptor complex A protein complex that binds interleukin-23. The complex comprises two subunits, including the same beta subunit found in the interleukin-12 receptor.
interleukin-27 complex A protein complex that is composed of an interleukin-27p28 subunit (product of the IL27 gene) and an EBI3 subunit and is secreted into the extracellular space.
interleukin-28 receptor complex A protein complex that binds interleukin-28 and interleukin-29. Composed of two subunits, IL-28R alpha and IL-10R beta.
interleukin-3 receptor complex A protein complex that binds interleukin-3; comprises an alpha and a beta subunit. The alpha chain is specific to the interleukin-3 receptor, whereas the beta chain is shared with the receptors for granulocyte-macrophage colony-stimulating factor and interleukin-5.
interleukin-35 complex A protein complex that is composed of an interleukin-12 alpha subunit (p35, product of the IL12A gene) and an EBI3 subunit and is secreted into the extracellular space.
interleukin-4 receptor complex A protein complex that binds interleukin-4 (IL-4) and consists of an alpha chain that binds IL-4 with high affinity and a gamma common chain that also forms part of the interleukin-2 receptor.
interleukin-5 receptor complex A protein complex that binds interleukin-3; comprises an alpha and a beta subunit. The alpha chain is specific to the interleukin-5 receptor, whereas the beta chain is shared with the receptors for granulocyte-macrophage colony-stimulating factor and interleukin-3.
interleukin-6 receptor complex A hexameric protein complex consisting of two molecules each of interleukin-6, interleukin-6 receptor alpha chain, and gp-130.
interleukin-9 receptor complex A protein complex that binds interleukin-9; comprises an alpha and a beta subunit. The alpha chain is specific to the interleukin-9 receptor, whereas the beta chain is shared with the receptors for several other interleukins.
interleukin4-interleukin-4 receptor complex A protein complex that is formed by the association of a heterodimeric interleukin-4 receptor complex with an interleukin-4 molecule.
intermediate filament A cytoskeletal structure that forms a distinct elongated structure, characteristically 10 nm in diameter, that occurs in the cytoplasm of eukaryotic cells. Intermediate filaments form a fibrous system, composed of chemically heterogeneous subunits and involved in mechanically integrating the various components of the cytoplasmic space. Intermediate filaments may be divided into five chemically distinct classes: Type I, acidic keratins; Type II, basic keratins; Type III, including desmin, vimentin and others; Type IV, neurofilaments and related filaments; and Type V, lamins.
intermediate filament cytoskeleton Cytoskeletal structure made from intermediate filaments, typically organized in the cytosol as an extended system that stretches from the nuclear envelope to the plasma membrane. Some intermediate filaments run parallel to the cell surface, while others traverse the cytosol; together they form an internal framework that helps support the shape and resilience of the cell.
intermediate-density lipoprotein particle A triglyceride-rich lipoprotein particle that typically contains APOB100, APOE and APOCs and has a density of 1.006-1.019 g/ml and a diameter of between 25-30 nm. IDL particles are found in blood and are formed by the delipidation of very-low-density lipoprotein particles (VLDL). IDL particles are removed from blood by the liver, following binding to the APOE receptor, or are converted to low-density lipoprotein (LDL).
interphase microtubule organizing center A microtubule organizing center found in interphase cells, which organize a longitudinal array of three to five MT bundles from the nuclear envelope during interphase. Each MT bundle is composed of two to seven MTs arranged in an antiparallel configuration, with the dynamic MT plus ends extending toward the cell tips and stable minus ends near the nucleus.
interphotoreceptor matrix A specialized extracellularc matrix that surrounds the photoreceptors of the retina and lies between them and the apical surface of the retinal pigment epithelium. The IPM has been implicated in several important activities required for photoreceptor function and maintenance.
interstitial matrix A type of extracellular matrix found in interstitial connective tissue, characterized by the presence of fibronectins, proteoglycans, and types I, III, V, VI, VII and XII collagens.
intine The innermost of the major layers of the pollen grain wall which underlies the exine and borders the cytoplasm.
intracellular The living contents of a cell; the matter contained within (but not including) the plasma membrane, usually taken to exclude large vacuoles and masses of secretory or ingested material. In eukaryotes it includes the nucleus and cytoplasm.
intracellular canaliculus An apical plasma membrane part that forms a narrow enfolded luminal membrane channel, lined with numerous microvilli, that appears to extend into the cytoplasm of the cell. A specialized network of intracellular canaliculi is a characteristic feature of parietal cells of the gastric mucosa in vertebrates.
intracellular ferritin complex A ferritin complex located in the cell. Intracellular ferritin complexes contain 24 subunits, in a mixture of L (light) chains and H (heavy) chains.
intracellular immature spore A cell or part of the cell that constitutes an early developmental stage of a spore, a small reproductive body that is highly resistant to desiccation and heat and is capable of growing into a new organism, produced especially by certain bacteria, fungi, algae, and nonflowering plants.
intracellular membrane-bounded organelle Organized structure of distinctive morphology and function, bounded by a single or double lipid bilayer membrane and occurring within the cell. Includes the nucleus, mitochondria, plastids, vacuoles, and vesicles. Excludes the plasma membrane.
intracellular non-membrane-bounded organelle Organized structure of distinctive morphology and function, not bounded by a lipid bilayer membrane and occurring within the cell. Includes ribosomes, the cytoskeleton and chromosomes.
intracellular organelle Organized structure of distinctive morphology and function, occurring within the cell. Includes the nucleus, mitochondria, plastids, vacuoles, vesicles, ribosomes and the cytoskeleton. Excludes the plasma membrane.
intracellular organelle lumen An organelle lumen that is part of an intracellular organelle.
intracellular organelle part A constituent part of an intracellular organelle, an organized structure of distinctive morphology and function, occurring within the cell. Includes constituent parts of the nucleus, mitochondria, plastids, vacuoles, vesicles, ribosomes and the cytoskeleton but excludes the plasma membrane.
intracellular part Any constituent part of the living contents of a cell; the matter contained within (but not including) the plasma membrane, usually taken to exclude large vacuoles and masses of secretory or ingested material. In eukaryotes it includes the nucleus and cytoplasm.
intraciliary transport particle A nonmembrane-bound oligomeric protein complex that participates in bidirectional transport of molecules (cargo) along axonemal microtubules.
intraciliary transport particle a The smaller subcomplex of the intraciliary transport particle; characterized complexes have molecular weights of 710-760 kDa.
intraciliary transport particle b The larger subcomplex of the intraciliary transport particle; characterized complexes have molecular weights around 550 kDa.
intraconoid microtubule A microtubule located such that it threads through the conoid and projects through the polar ring.
intrinsic component of endoplasmic reticulum membrane The component of the endoplasmic reticulum membrane consisting of gene products and protein complexes that have some covalently attached part (e.g. peptide sequence or GPI anchor), which spans or is embedded in one or both leaflets of the membrane.
intrinsic component of golgi membrane The component of the Golgi membrane consisting of gene products and protein complexes that have some covalently attached part (e.g. peptide sequence or GPI anchor), which spans or is embedded in one or both leaflets of the membrane.
intrinsic component of membrane The component of a membrane consisting of the gene products having some covalently attached portion, for example part of a peptide sequence or some other covalently attached group such as a GPI anchor, which spans or is embedded in one or both leaflets of the membrane.
intrinsic component of mitochondrial inner membrane The component of the mitochondrial inner membrane consisting of the gene products that have some covalently attached part (e.g. peptide sequence or GPI anchor) which spans or is embedded in one or both leaflets of the membrane.
intrinsic component of mitochondrial membrane The component of the mitochondrial membrane consisting of the gene products that have some covalently attached part (e.g. peptide sequence or GPI anchor) which spans or is embedded in one or both leaflets of the membrane.
intrinsic component of organelle membrane The component of the organelle membrane consisting of the gene products that have some covalently attached part (e.g. peptide sequence or GPI anchor) which spans or is embedded in one or both leaflets of the membrane.
intrinsic component of plasma membrane The component of the plasma membrane consisting of gene products and protein complexes that have some covalently attached part (e.g. peptide sequence or GPI anchor), which spans or is embedded in one or both leaflets of the membrane.
invadopodium A cell projection that emerges from the ECM-facing surface of a cell, is enriched in actin and associated cytoskeletal proteins, and displays localized proteolytic activity toward the substrate.
invadopodium membrane The portion of the plasma membrane surrounding an invadopodium.
invertasome A complex formed by a recombinase, a regulatory protein, and the DNA sequences bound by each protein; catalyzes a reversible site-specific recombination reaction that results in the alternate expression of one or more genes in various contexts.
investment cone A cytoskeletal part that consists of a microfilament-rich cone that forms round each nucleus in a spermatogenic cyst and translocates the length of the cyst during sperm individualization.
ion channel complex A protein complex that spans a membrane and forms a water-filled channel across the phospholipid bilayer allowing selective ion transport down its electrochemical gradient.
ionotropic glutamate receptor complex A multimeric assembly of four or five subunits which form a structure with an extracellular N-terminus and a large loop that together form the ligand binding domain. The C-terminus is intracellular. The ionotropic glutamate receptor complex itself acts as a ligand-gated ion channel; on binding glutamate, charged ions pass through a channel in the center of the receptor complex.
ipaf inflammasome complex A protein complex that consists of three components, IPAF, NAIP and caspase-1, and includes among its functions the sensing of flagellin derived from Legionella pneumophila, Salmonella typhimurium, Pseudomonas aeruginosa and Shigella flexneri.
iridosome A tissue-specific, membrane-bounded cytoplasmic organelle within which purines crystalize in reflective stacks. Iridosomes are synthesized in iridophore cells and are silver, gold or iridescent in appearance.
isw1 complex A protein complex that contains an Isw1 subunit from the ISWI-family of ATPases and acts to modify chromatin structure.
iswi-type complex Any nuclear protein complex that contains an ATPase subunit of the imitation switch (ISWI) family. ISWI ATPases are involved in assembling chromatin and in sliding and spacing nucleosomes to regulate transcription of nuclear RNA polymerases I, II, and III and also DNA replication, recombination and repair.
junctional membrane complex Complex formed in muscle cells between the membrane of the sarcoplasmic reticulum and invaginations of the plasma membrane (T-tubules).
junctional sarcoplasmic reticulum membrane The part of the sarcoplasmic reticulum membrane that contains calcium release channels, is devoted to calcium release and is juxtaposed to transverse tubule membrane. The junctional sarcoplasmic reticulum membrane consists of the junctional region of the terminal cisterna membrane.
juxtaparanode region of axon A region of an axon near a node of Ranvier that is between the paranode and internode regions.
karyomere A membrane-bound intermediate cleavage-stage structure of individual or groups of chromosomes that coalesces and fuses with other karyomeres to form a nucleus during interphase. Karyomere formation occurs in blastomeres undergoing rapid cell division.
keratin filament A filament composed of acidic and basic keratins (types I and II), typically expressed in epithelial cells. The keratins are the most diverse classes of IF proteins, with a large number of keratin isoforms being expressed. Each type of epithelium always expresses a characteristic combination of type I and type II keratins.
kinesin complex Any complex that includes a dimer of molecules from the kinesin superfamily, a group of related proteins that contain an extended region of predicted alpha-helical coiled coil in the main chain that likely produces dimerization. The native complexes of several kinesin family members have also been shown to contain additional peptides, often designated light chains as all of the noncatalytic subunits that are currently known are smaller than the chain that contains the motor unit. Kinesin complexes generally possess a force-generating enzymatic activity, or motor, which converts the free energy of the gamma phosphate bond of ATP into mechanical work.
kinesin i complex A complex of two kinesin heavy chains and two kinesin light chains.
kinesin ii complex A complex consisting of two distinct motor subunits that form a heterodimer complexed with a third non-motor accessory subunit, the kinesin associated protein or KAP; the KIF3 heterodimer interacts via its C-terminal portion with KAP, which is thought to regulate the binding of the motor to cargo membranes.
kinetochore A multisubunit complex that is located at the centromeric region of DNA and provides an attachment point for the spindle microtubules.
kinetochore microtubule Any of the spindle microtubules that attach to the kinetochores of chromosomes by their plus ends, and maneuver the chromosomes during mitotic or meiotic chromosome segregation.
kinetoplast A sub-structure within the large single mitochondrion of kinetoplastid parasites and which is closely associated with the flagellar pocket and basal body of the flagellum.
kinocilium A nonmotile primary cilium that is found at the apical surface of auditory receptor cells. The kinocilium is surrounded by actin-based stereocilia.
ku70:ku80 complex Heterodimeric protein complex composed of a 70 kDa and a 80 kDa subunit, binds DNA through a channel formed by the heterodimer. Functions in DNA double stranded break repair, chromosome maintenance, transcription regulation, V(D)J recombination, and activation of DNA-PK.
lamellar body A membrane-bounded organelle, specialized for the storage and secretion of various substances (surfactant phospholipids, glycoproteins and acid phosphates) which are arranged in the form of tightly packed, concentric, membrane sheets or lamellae. Has some similar properties to, but is distinct from, a lysosome.
lamellar body membrane The lipid bilayer surrounding a lamellar body. A lamellar body is a membrane-bounded organelle, specialized for the storage and secretion of various substances (surfactant phospholipids, glycoproteins and acid phosphates) which are arranged in the form of tightly packed, concentric, membrane sheets or lamellae. Has some similar properties to, but is distinct from, a lysosome.
lamellipodium A thin sheetlike process extended by the leading edge of a crawling fibroblast; contains a dense meshwork of actin filaments.
lamin filament Any of a group of intermediate-filament proteins that form the fibrous matrix on the inner surface of the nuclear envelope. They are classified as lamins A, B and C.
lamina densa The electron-dense layer of the basal lamina; lies just below the lamina lucida.
lamina lucida The electron-lucent layer of the basal lamina adjacent to the basal plasma membrane of the cells that rest on the lamina.
lamina reticularis A layer of the basal lamina that contains collagen fibrils and connects the basal lamina to the underlying connective tissue.
laminated body Inclusion body characterized by regularly spaced sheets of tubules arranged in a whorl pattern resembling a fingerprint. Laminated bodies have been observed in neurons of the lateral geniculate nucleus.
laminin complex A large, extracellular glycoprotein complex composed of three different polypeptide chains, alpha, beta and gamma. Provides an integral part of the structural scaffolding of basement membranes.
laminin-1 complex A laminin complex composed of alpha1, beta1 and gamma1 polypeptide chains.
laminin-10 complex A laminin complex composed of alpha5, beta1 and gamma1 polypeptide chains.
laminin-11 complex A laminin complex composed of alpha5, beta2 and gamma1 polypeptide chains.
laminin-2 complex A laminin complex composed of alpha2, beta1 and gamma1 polypeptide chains.
laminin-3 complex A laminin complex composed of alpha1, beta2 and gamma1 polypeptide chains.
laminin-4 complex A laminin complex composed of alpha2, beta2 and gamma1 polypeptide chains.
laminin-5 complex A laminin complex composed of alpha3, beta3 and gamma2 polypeptide chains.
laminin-6 complex A laminin complex composed of alpha3, beta1 and gamma1 polypeptide chains.
laminin-7 complex A laminin complex composed of alpha3, beta2 and gamma1 polypeptide chains.
laminin-8 complex A laminin complex composed of alpha4, beta1 and gamma1 polypeptide chains.
laminin-9 complex A laminin complex composed of alpha4, beta2 and gamma1 polypeptide chains.
large latent transforming growth factor-beta complex A protein complex containing latency-associated proteins (LAPs), mature disulphide-linked dimeric TGF-beta, and latent TGF-beta binding proteins (LTBPs). TGF-beta is mostly secreted as part of the large latent complex, and must be subsequently released from the LLC in order to bind to cell surface receptors.
large ribosomal subunit The larger of the two subunits of a ribosome. Two sites on the ribosomal large subunit are involved in translation, namely the aminoacyl site (A site) and peptidyl site (P site).
larval serum protein complex A multisubunit protein complex which, in Drosophila, is a heterohexamer of three subunits, alpha, beta and gamma. The complex is thought to store amino acids for synthesis of adult proteins.
late endosome A prelysosomal endocytic organelle differentiated from early endosomes by lower lumenal pH and different protein composition. Late endosomes are more spherical than early endosomes and are mostly juxtanuclear, being concentrated near the microtubule organizing center.
late endosome lumen The volume enclosed by the membrane of a late endosome.
late endosome membrane The lipid bilayer surrounding a late endosome.
late recombination nodule An electron dense structure that is associated with meiotic chromosomes in pachytene during meiosis I.
lateral element A proteinaceous core found between sister chromatids during meiotic prophase.
lateral loop Non-compact myelin located adjacent to the nodes of Ranvier in a myelin segment. These non-compact regions include cytoplasm from the cell responsible for synthesizing the myelin. Lateral loops are found in the paranodal region adjacent to the nodes of Ranvier, while Schmidt-Lantermann clefts are analogous structures found within the compact myelin internode.
lateral plasma membrane The portion of the plasma membrane at the lateral side of the cell. In epithelial cells, lateral plasma membranes are on the sides of cells which lie at the interface of adjacent cells.
leading edge membrane The portion of the plasma membrane surrounding the leading edge of a motile cell.
leucoplast A colorless plastid involved in the synthesis of monoterpenes.
leucosome A tissue-specific, membrane-bounded cytoplasmic organelle within which uric acid and/or purines crystalize in reflective stacks. Leucosomes are synthesized in leucophore cells and have a whitish cast.
lewy body Cytoplasmic, spherical inclusion commonly found in damaged neurons, and composed of abnormally phosphorylated, neurofilament proteins aggregated with ubiquitin and alpha-synuclein.
lewy body core The center portion of a Lewy body. In Parkinson's disease, it contains a matted meshwork of filaments.
lewy body corona The periphery of a Lewy body. In Parkinson's disease, it contains spherical accumulations of filaments arranged in a loose, radiating array.
lewy body-like hyaline inclusion Cytoplasmic inclusion found in neurons. It consists of filaments and granular materials, exhibits a dense core with a rough peripheral halo and lacks a limiting membrane. The filaments of these inclusions are composed of approximately 15-25 nm granule-coated fibrils in association with normal 10-nm neurofilaments.
lewy neurite Elongated neuronal process, often with side branches and more than one branching point, described in brains of patients with Parkinson's disease. Lewy neurites stain positively for ubiquitin in brainstem and forebrain regions affected in Parkinson's disease.
light-harvesting complex A protein-pigment complex that may be closely or peripherally associated to photosynthetic reaction centers that participate in harvesting and transferring radiant energy to the reaction center.
light-harvesting complex, core complex Light harvesting complex associated with the reaction complex of photosynthetic purple bacteria.
light-harvesting complex, peripheral complex Bacteriochlorophyll a binding complex that is peripherally associated to the bacterial reaction center.
linc complex
linear element A proteinaceous scaffold associated with S. pombe chromosomes during meiotic prophase. Linear elements have a structure related to but not equivalent to the synaptonemal complex.
lipid particle An intracellular non-membrane-bounded organelle comprising a matrix of coalesced lipids surrounded by a phospholipid monolayer. May include associated proteins.
lipid tube A macromolecular complex that contains a tube of lipid surrounded by a protein coat.
lipopolysaccharide receptor complex A multiprotein complex that consists of at least three proteins, CD14, TLR4, and MD-2, each of which is glycosylated and which functions as a lipopolysaccharide (LPS) receptor that primes the innate immune response against bacterial pathogens.
longitudinal sarcoplasmic reticulum The portion of the free sarcoplasmic reticulum consisting of longitudinal tubules that connect terminal cisternae.
low-density lipoprotein particle A lipoprotein particle, rich in cholesterol esters and low in triglycerides that is typically composed of APOB100 and APOE and has a density of 1.02-1.06 g/ml and a diameter of between 20-25 nm. LDL particles are formed from VLDL particles (via IDL) by the loss of triglyceride and gain of cholesterol ester. They transport endogenous cholesterol (and to some extent triglycerides) from peripheral tissues back to the liver.
lsd1/2 complex A nucleosome-binding protein complex that comprises two SWIRM domain histone demethylases and two PHD finger proteins. The complex is involved in transcriptional regulation via heterochromatic silencing and the regulation of chromatin boundary formation, and was first identified in fission yeast.
lubac complex A ubiquitin ligase complex that catalyzes linear head-to-tail polyubiquitin conjugation on its targets. In human the complex consists of RBCK1, RNF31 and SHARPIN, and has an MW of approximately 600 kDa, suggesting a heteromultimeric assembly of its subunits. LUBAC stands for Linear Ubiquitin Chain Assembly Complex.
luminal surveillance complex A multiprotein complex that recognizes ERAD-luminal misfolded substrates and brings them to the ubiquitination/extraction machinery. In yeast, this complex consists of Yos9p, Kar2p and Hrd3p proteins.
lysosomal glycocalyx The polysaccharide-based coating on the inner side of a lysosomal membrane that protects it from digestion by lysosomal enzymes.
lysosomal lumen The volume enclosed within the lysosomal membrane.
lysosomal membrane The lipid bilayer surrounding the lysosome and separating its contents from the cell cytoplasm.
lysosomal multienzyme complex A protein complex found in the lysosome that contains beta-galactosidase, cathepsin A, alpha-neuraminidase and N-acetylgalactosamine-6-sulfate sulfatase, and is involved in glycosaminoglycan catabolism.
lysosome A small lytic vacuole that has cell cycle-independent morphology and is found in most animal cells and that contains a variety of hydrolases, most of which have their maximal activities in the pH range 5-6. The contained enzymes display latency if properly isolated. About 40 different lysosomal hydrolases are known and lysosomes have a great variety of morphologies and functions.
lysp100-associated nuclear domain A nuclear body that is enriched in the lymphoid cell-specific protein LYSp100B; LANDs are globular, electron-dense structures and are morphologically distinct from the annular structures characteristic of PML bodies.
lytic vacuole A vacuole that is maintained at an acidic pH and which contains degradative enzymes, including a wide variety of acid hydrolases.
m band The midline of aligned thick filaments in a sarcomere; location of specific proteins that link thick filaments. Depending on muscle type the M band consists of different numbers of M lines.
m-aaa complex Protease complex of the mitochondrial inner membrane that is involved in mitochondrial protein turnover and in processing of proteins imported into mitochondria.
macromolecular complex A stable assembly of two or more macromolecules, i.e. proteins, nucleic acids, carbohydrates or lipids, in which the constituent parts function together.
macronucleus A membrane-bounded organelle of ciliated protozoan cells that contains polyploid copies of a portion of the cell's complete genome. Transcription of genes occurs in macronuclei. Some ciliate species may contain multiple macronuclei per cell.
macrophage migration inhibitory factor receptor complex A protein complex that binds macrophage migration inhibitory factor. Comprises CD74 and CD44 cell surface proteins.
macropinocytic cup A cell projection that forms at the site of macropinocytosis, a form of endocytosis that results in the uptake of relatively large amounts of extracellular fluid. The macropinocytic cup membrane selectively excludes certain proteins, such as H36 or PM4C4 in Dictyostelium, and the underlying cytoskeleton is enriched in F-actin and coronin.
macropinosome A membrane-bounded, uncoated intracellular vesicle formed by the process of macropinocytosis.
mad-max complex A transcriptional repressor complex that consists of a heterodimer of the bHLH-ZIP proteins Mad and Max.
mad-max-msin3a complex A transcriptional repressor complex that contains a heterodimer of the bHLH-ZIP proteins Mad and Max, plus mSin3A, a homolog of the yeast Sin3p.
main axon The main axonal trunk, as opposed to the collaterals.
male germ cell nucleus The nucleus of a male germ cell, a reproductive cell in males.
male pronucleus The pronucleus originating from the spermatozoa that was involved in fertilization.
manchette A conical shaped array of microtubules that completely covers the nucleus of a spermatid, thought to be involved in sperm head elongation.
mannosome A specialised tubular organelle, assembled in hexagonal bundles within an external membrane. Mannosomes are specific to molluscs and are thought to be involved in a general stress reaction.
mannosyltransferase complex A complex that posseses mannosyltransferase activity.
mast cell granule Coarse, bluish-black staining cytoplasmic granules, bounded by a plasma membrane and found in mast cells and basophils. Contents include histamine, heparin, chondroitin sulfates, chymase and tryptase.
mating projection The projection formed by unicellular fungi in response to mating pheromone.
mating projection tip The apex of the mating projection in unicellular fungi exposed to mating pheromone; site of polarized growth.
mcm complex A hexameric protein complex required for the initiation and regulation of DNA replication.
mcm core complex A protein complex that contains Mcm4, Mcm6, and Mcm7 proteins, and possesses DNA helicase activity. In the heterohexameric MCM complex, the Mcm4/6/7 proteins form a stable core, and Mcm2, Mcm3, and Mcm5 are more peripherally associated.
mcm8-mcm9 complex A hexameric protein complex composed of MCM8 and MCM9 and involved in homologous recombination repair following DNA interstrand cross-links.
meco complex A highly stable complex composed of the ATAC complex and the mediator complex (also called TRAP or MED). MECO binds and regulates the transcription of a subset of non-coding RNAs transcribed by RNA polymerase II.
medial cortex A medial cortical band overlaying the nucleus which acts as a landmark for contractile ring positioning and plays a role in cell cycle regulation.
medial cortical node A protein complex that contains the mid1, cdr2, wee1, klp8, and blt1 proteins, and is involved in contractile ring localization. Medial cortical node complexes appear as cortical dots in the middle of the cell during interphase, and function to recruit other ring components in early mitosis.
mediator complex A protein complex that interacts with the carboxy-terminal domain of the largest subunit of RNA polymerase II and plays an active role in transducing the signal from a transcription factor to the transcriptional machinery. The mediator complex is required for activation of transcription of most protein-coding genes, but can also act as a transcriptional corepressor. The Saccharomyces complex contains several identifiable subcomplexes: a head domain comprising Srb2, -4, and -5, Med6, -8, and -11, and Rox3 proteins; a middle domain comprising Med1, -4, and -7, Nut1 and -2, Cse2, Rgr1, Soh1, and Srb7 proteins; a tail consisting of Gal11p, Med2p, Pgd1p, and Sin4p; and a regulatory subcomplex comprising Ssn2, -3, and -8, and Srb8 proteins. Metazoan mediator complexes have similar modular structures and include homologs of yeast Srb and Med proteins.
megasome Large, cysteine proteinase rich lysosomes, often found in the amastigote (an intracytoplasmic, nonflagellated form of the parasite) stage of Leishmania species belonging to the mexicana complex.
megasporocyte nucleus The nucleus of a megasporocyte, a diploid cell that undergoes meiosis to produce four megaspores, and its descendents.
meiotic cohesin complex A cohesin complex that mediates sister chromatid cohesion during meiosis; has a subunit composition distinct from that of the mitotic cohesin complex.
meiotic recombination initiation complex A protein complex that initiates the formation of double-strand breaks (DSBs) required for meiotic recombination. Consists of a protein that catalyses formation of the double-strand breaks (Spo11 in S. cerevisiae and Rec12 in S. pombe), and a number of accessory proteins.
meiotic spindle A spindle that forms as part of meiosis. Several proteins, such as budding yeast Spo21p, fission yeast Spo2 and Spo13, and C. elegans mei-1, localize specifically to the meiotic spindle and are absent from the mitotic spindle.
meiotic spindle pole body The microtubule organizing center on a spindle that forms as part of meiosis; functionally homologous to the animal cell centrosome.
melanosome A tissue-specific, membrane-bounded cytoplasmic organelle within which melanin pigments are synthesized and stored. Melanosomes are synthesized in melanocyte cells.
melanosome lumen The volume enclosed by the melanosome membrane.
melanosome membrane The lipid bilayer surrounding a melanosome.
membrane Double layer of lipid molecules that encloses all cells, and, in eukaryotes, many organelles; may be a single or double lipid bilayer; also includes associated proteins.
membrane attack complex A protein complex produced by sequentially activated components of the complement cascade inserted into a target cell membrane and forming a pore leading to cell lysis via ion and water flow.
membrane coat Any of several different proteinaceous coats that can associate with membranes. Membrane coats include those formed by clathrin plus an adaptor complex, the COPI and COPII complexes, and possibly others. They are found associated with membranes on many vesicles as well as other membrane features such as pits and perhaps tubules.
membrane part Any constituent part of a membrane, a double layer of lipid molecules that encloses all cells, and, in eukaryotes, many organelles; may be a single or double lipid bilayer; also includes associated proteins.
membrane raft Any of the small (10-200 nm), heterogeneous, highly dynamic, sterol- and sphingolipid-enriched membrane domains that compartmentalize cellular processes. Small rafts can sometimes be stabilized to form larger platforms through protein-protein and protein-lipid interactions.
membrane region A membrane that is a part of a larger membrane. Examples include the apical region of the plasma membrane of an epithelial cell and the various regions of the endoplasmic reticulum membrane.
membrane stack A configuration of endoplasmic reticulum (ER) found in Purkinje cells in the cerebellum and in axons in the lateral vestibular nucleus, consisting of parallel and interconnecting tubules whose outer surfaces are covered by particles or ringlike structures.
membrane-bounded organelle Organized structure of distinctive morphology and function, bounded by a single or double lipid bilayer membrane. Includes the nucleus, mitochondria, plastids, vacuoles, and vesicles. Excludes the plasma membrane.
membrane-bounded vesicle Any small, fluid-filled, spherical organelle enclosed by a lipid bilayer.
membrane-enclosed lumen The enclosed volume within a sealed membrane or between two sealed membranes. Encompasses the volume enclosed by the membranes of a particular organelle, e.g. endoplasmic reticulum lumen, or the space between the two lipid bilayers of a double membrane surrounding an organelle, e.g. nuclear envelope lumen.
meprin a complex A protein complex that is located in the cell membrane, and is involved in the metabolism of peptides, including neuropeptides. The complex has metalloendopeptidase activity that catalyzes the hydrolysis of protein and peptide substrates, preferentially on carboxyl side of hydrophobic residues.
merozoite dense granule Electron-dense organelle with a granular internal matrix found throughout the merozoite life cycle stage of apicomplexan parasites; contains proteins destined to be secreted into the parasitophorous vacuole following parasite invasion of a host cell.
mesaxon Portion of the ensheathing process (either myelin or non-myelin) where the enveloping lips of the ensheathing cell come together so that their apposed plasma membranes run parallel to each other, separated by a cleft 12 nm wide.
mesosome An intracellular, often complex, membranous structure, sometimes with additional membranous lamellae inside, found in bacteria. They are associated with synthesis of DNA and secretion of proteins.
metaphase plate The intracellular plane, located halfway between the poles of the spindle, where chromosomes align during metaphase of mitotic or meiotic nuclear division.
methane monooxygenase complex A protein complex that possesses methane monooxygenase activity; dimeric and trimeric complexes have been characterized.
methanol-com methyltransferase complex A heterotrimeric protein complex composed of a methanol methyltransferase subunit, a corrinoid protein and a methanol-specific corrinoid:coenzyme M methyltransferase subunit. Catalyzes the transfer of a methyl group from methanol to coenzyme M as part of the pathway of methanogenesis from methanol.
methionine adenosyltransferase complex A multimeric enzyme complex composed of variable numbers of catalytic alpha subunits, and noncatalytic beta subunits. The beta subunits are believed to have a regulatory function. The enzyme complex catalyzes the synthesis of S-adenosylmethionine (AdoMet), which is the major methyl group donor, participating in the methylation of proteins, DNA, RNA, phospholipids, and other small molecules.
methyl-tetrahydromethanopterin:coenzyme m methyltransferase complex A protein complex consisted of eight polypeptides. This complex catalyzes the formation of methyl-coenzyme M and H4MPT from N5-methyl-H4MPT and CoM during methanogenesis.
methylosome A large (20 S) protein complex that possesses protein arginine methyltransferase activity and modifies specific arginines to dimethylarginines in the arginine- and glycine-rich domains of several spliceosomal Sm proteins, thereby targeting these proteins to the survival of motor neurons (SMN) complex for assembly into small nuclear ribonucleoprotein (snRNP) core particles. Proteins found in the methylosome include the methyltransferase JBP1 (PRMT5), pICln (CLNS1A), MEP50 (WDR77), and unmethylated forms of SM proteins that have RG domains.
methyltransferase complex A protein complex that possesses methyltransferase activity.
mhc class i peptide loading complex A large, multisubunit complex which consists of the MHC class I-beta 2 microglobulin dimer, the transporter associated with antigen presentation (TAP), tapasin (an MHC-encoded membrane protein), the chaperone calreticulin and the thiol oxidoreductase ERp57. Functions in the assembly of peptides with newly synthesized MHC class I molecules.
mhc class i protein complex A transmembrane protein complex composed of a MHC class I alpha chain and an invariant beta2-microglobin chain, and with or without a bound peptide antigen. Class I here refers to classical class I molecules.
mhc class ib protein complex A transmembrane protein complex composed of a MHC class Ib alpha chain and, in most cases, an invariant beta2-microglobin chain, and with or without a bound peptide or lipid antigen. Class Ib here refers to non-classical class I molecules, such as those of the CD1 or HLA-E gene families.
mhc class ii protein complex A transmembrane protein complex composed of an MHC class II alpha and MHC class II beta chain, and with or without a bound peptide or polysaccharide antigen.
mhc protein complex A transmembrane protein complex composed of an MHC alpha chain and, in most cases, either an MHC class II beta chain or an invariant beta2-microglobin chain, and with or without a bound peptide, lipid, or polysaccharide antigen.
micro-ribonucleoprotein complex A complex containing both protein and micro-RNA (miRNA) molecules. miRNAs are approximately 22 nucleotide noncoding RNAs derived from endogenous genes; they are processed from the stem of a longer hairpin like structure termed a pre-miRNA.
microbody Cytoplasmic organelles, spherical or oval in shape, that are bounded by a single membrane and contain oxidative enzymes, especially those utilizing hydrogen peroxide (H2O2).
microbody lumen The volume enclosed by the membranes of a microbody.
microbody membrane The lipid bilayer surrounding a microbody.
microbody part Any constituent part of a microbody, a cytoplasmic organelle, spherical or oval in shape, that is bounded by a single membrane and contains oxidative enzymes, especially those utilizing hydrogen peroxide (H2O2).
microfibril Extracellular matrix components occurring independently or along with elastin. Thought to have force-bearing functions in tendon. In addition to fibrillins, microfibrils may contain other associated proteins.
microneme A small, elongated secretory organelle that forms part of the apical complex, located along the main axis of an apicomplexan parasite cell within the extreme apical region and at the periphery under the inner membrane complex. Of the specialized secretory compartments identified in apicomplexans, micronemes discharge their contents first, during initial contact of the parasite's apical pole with the host cell surface. Micronemal proteins function during parasite attachment and penetration into the target cell.
microneme lumen The volume enclosed by the microneme membrane.
microneme membrane The lipid bilayer surrounding a microneme.
micronucleus A membrane-bounded organelle of ciliated protozoan cells that contains a diploid copy of the cell's complete genome. Sections of contiguous sequence in the macronucleus are often interrupted by internal eliminated sequences (IES), and may be permuted, in micronuclei. Genic transcription is not found in micronuclei. Some ciliate species may contain multiple micronuclei per cell.
micropexophagy-specific membrane apparatus A membrane-bounded flattened sac that is formed during micropexophagy between the membrane tips of an engulfing vacuole, completing the engulfment and sequestration of peroxisomes from the cytosol, and forming a micropexophagic body within the lumen of the vacuole.
micropinosome A membrane-bounded, uncoated intracellular vesicle formed by the process of micropinocytosis.
microprocessor complex A protein complex that binds to heme and to pri-miRNAs, and is required for the formation of a pre-microRNA (pre-miRNA), the initial step of microRNA (miRNA) biogenesis. The complex is composed of the double-stranded-RNA-specific RNase Drosha (also called RNASEN) and the RNA-binding protein DGCR8 (heme-free or heme-bound forms). Within the complex, DGCR8 function as a molecular anchor necessary for the recognition of pri-miRNA at dsRNA-ssRNA junction and directs RNASEN/Drosha to cleave the 3' and 5' strands of a stem-loop to release hairpin-shaped pre-miRNAs.
micropyle An external encapsulating structure part of the chorion. A single cone-shaped specialization that forms an opening in the chorion that allows sperm entry into the egg prior to fertilization.
microspike A dynamic, actin-rich projection extending from the surface of a migrating animal cell.
microsporocyte nucleus The nucleus of the microsporocyte. The microsporocyte is a diploid cell in which meiosis will occur, resulting in four microspores. A microspore is a spore that, in vascular plants, gives rise to a male gametophyte.
microtubule Any of the long, generally straight, hollow tubes of internal diameter 12-15 nm and external diameter 24 nm found in a wide variety of eukaryotic cells; each consists (usually) of 13 protofilaments of polymeric tubulin, staggered in such a manner that the tubulin monomers are arranged in a helical pattern on the microtubular surface, and with the alpha/beta axes of the tubulin subunits parallel to the long axis of the tubule; exist in equilibrium with pool of tubulin monomers and can be rapidly assembled or disassembled in response to physiological stimuli; concerned with force generation, e.g. in the spindle.
microtubule associated complex Any multimeric complex connected to a microtubule.
microtubule bundle An arrangement of closely apposed microtubules running parallel to each other.
microtubule cytoskeleton The part of the cytoskeleton (the internal framework of a cell) composed of microtubules and associated proteins.
microtubule organizing center An intracellular structure that can catalyze gamma-tubulin-dependent microtubule nucleation and that can anchor microtubules by interacting with their minus ends, plus ends or sides.
microtubule organizing center attachment site A region of the nuclear envelope to which a microtubule organizing center (MTOC) attaches; protein complexes embedded in the nuclear envelope mediate direct or indirect linkages between the microtubule cytoskeleton and the nuclear envelope.
microtubule organizing center part Any constituent part of a microtubule organizing center, a region in a eukaryotic cell, such as a centrosome or basal body, from which microtubules grow.
microtubule plus-end The growing (plus) end of a microtubule. In vitro, microtubules polymerize more quickly at the plus end than at the minus end. In vivo, microtubule growth occurs only at the plus end, and the plus end switches between periods of growth and shortening, a behavior known as dynamic instability.
microvillus Thin cylindrical membrane-covered projections on the surface of an animal cell containing a core bundle of actin filaments. Present in especially large numbers on the absorptive surface of intestinal cells.
microvillus membrane The portion of the plasma membrane surrounding a microvillus.
midbody A thin cytoplasmic bridge formed between daughter cells at the end of cytokinesis. The midbody forms where the contractile ring constricts, and may persist for some time before finally breaking to complete cytokinesis.
middle lamella Layer of intercellular material, chiefly pectic substances, cementing together the primary walls of contiguous cells.
minus-end kinesin complex Any complex that includes a dimer of molecules from the kinesin superfamily and any associated proteins, and moves towards the minus end of a microtubule.
mis12/mind type complex A multiprotein kinetochore subcomplex that binds to centromeric chromatin and forms part of the inner kinetochore. It helps to recruit outer kinetochore subunits that will bind to microtubules. In humans, it consists of MIS12, DSN1, NSL1 and PMF1.
mis6-sim4 complex A protein complex that forms part of the inner centromere, which is involved in the loading of the centromeric histone h3 variant CENP-A onto centromeres and in centromere specific heterochromatin formation. The complex contains about 12 proteins, of which two are known as Mis6 and Sim4 in S. pombe and CENP-I and CENP-H in human.
mismatch repair complex Any complex formed of proteins that act in mismatch repair.
mitochondrial alpha-ketoglutarate dehydrogenase complex Mitochondrial complex that possesses alpha-ketoglutarate dehydrogenase activity.
mitochondrial chromosome A chromosome found in the mitochondrion of a eukaryotic cell.
mitochondrial cloud A prominent mass in the cytoplasm of previtellogenic oocytes. The cloud contains both mitochondria and electron-dense granulofibrillar material (GFM) and is the source of germinal granule material.
mitochondrial creatine kinase complex An octomeric protein complex having creatine kinase activity.
mitochondrial crista Any of the inward folds of the mitochondrial inner membrane. Their number, extent, and shape differ in mitochondria from different tissues and organisms. They appear to be devices for increasing the surface area of the mitochondrial inner membrane, where the enzymes of electron transport and oxidative phosphorylation are found. Their shape can vary with the respiratory state of the mitochondria.
mitochondrial crista junction A tubular structure of relatively uniform size that connects a mitochondrial crista to the mitochondrial inner boundary membrane.
mitochondrial degradosome A mitochondrial protein complex with 3' to 5' exoribonuclease activity that participates in intron-independent turnover and processing of mitochondrial transcripts. In humans, the mitochondrial degradosome is a pentameric complex, and in yeast it exists as a heterodimer.
mitochondrial derivative The major and minor mitochondrial derivatives are the mitochondria of the sperm tail and derive by the unfolding of the Nebenkern during flagellum elongation.
mitochondrial electron transfer flavoprotein complex A protein complex located in the mitochondrion. It contains flavin adenine dinucleotide (FAD) that, together with an acyl-CoA dehydrogenase, forms a system that oxidizes an acyl-CoA molecule and reduces ubiquinone and other acceptors in the mitochondrial electron transport system.
mitochondrial envelope The double lipid bilayer enclosing the mitochondrion and separating its contents from the cell cytoplasm; includes the intermembrane space.
mitochondrial fatty acid beta-oxidation multienzyme complex A complex that includes the long-chain 3-hydroxyacyl-CoA dehydrogenase and long-chain enoyl-CoA hydratase activities in two subunits (alpha and beta), catalyzing two steps of the fatty acid beta-oxidation cycle within the mitochondrial matrix.
mitochondrial inner membrane The inner, i.e. lumen-facing, lipid bilayer of the mitochondrial envelope. It is highly folded to form cristae.
mitochondrial inner membrane peptidase complex Protease complex of the mitochondrial inner membrane, consisting of at least two subunits, involved in processing of both nuclear- and mitochondrially-encoded proteins targeted to the intermembrane space.
mitochondrial inner membrane presequence translocase complex The protein transport machinery of the mitochondrial inner membrane that contains three essential Tim proteins: Tim17 and Tim23 are thought to build a preprotein translocation channel while Tim44 interacts transiently with the matrix heat-shock protein Hsp70 to form an ATP-driven import motor.
mitochondrial inner membrane protein insertion complex A multi-subunit complex embedded in the mitochondrial inner membrane that mediates insertion of carrier proteins into the inner membrane.
mitochondrial intermembrane space The region between the inner and outer lipid bilayers of the mitochondrial envelope.
mitochondrial intermembrane space protein transporter complex Soluble complex of the mitochondrial intermembrane space composed of various combinations of small Tim proteins; acts as a protein transporter to guide proteins to the Tim22 complex for insertion into the mitochondrial inner membrane.
mitochondrial large ribosomal subunit The larger of the two subunits of a mitochondrial ribosome. Two sites on the ribosomal large subunit are involved in translation: the aminoacyl site (A site) and peptidyl site (P site).
mitochondrial matrix The gel-like material, with considerable fine structure, that lies in the matrix space, or lumen, of a mitochondrion. It contains the enzymes of the tricarboxylic acid cycle and, in some organisms, the enzymes concerned with fatty acid oxidation.
mitochondrial membrane Either of the lipid bilayers that surround the mitochondrion and form the mitochondrial envelope.
mitochondrial membrane part Any constituent part of a mitochondrial membrane, either of the lipid bilayers that surround the mitochondrion and form the mitochondrial envelope.
mitochondrial nucleoid The region of a mitochondrion to which the DNA is confined.
mitochondrial outer membrane The outer, i.e. cytoplasm-facing, lipid bilayer of the mitochondrial envelope.
mitochondrial outer membrane translocase complex A large complex of the mitochondrial outer membrane that mediates transport of proteins into all mitochondrial compartments.
mitochondrial part Any constituent part of a mitochondrion, a semiautonomous, self replicating organelle that occurs in varying numbers, shapes, and sizes in the cytoplasm of virtually all eukaryotic cells. It is notably the site of tissue respiration.
mitochondrial permeability transition pore complex A protein complex that connects the inner and outer membranes of animal mitochondria and acts as a pore that can open transiently to allow free diffusion of solutes between the mitochondrial matrix and the cytosol. The pore complex is formed of the voltage-dependent anion channel (VDAC), the adenine nucleotide translocase (ANT) and cyclophilin-D (CyP-D).
mitochondrial processing peptidase complex A protein complex that consists of a catalytic alpha subunit (alpha-MPP) and a regulatory beta subunit (beta-MPP), and catalyzes the release of N-terminal targeting peptides from precursor proteins imported into the mitochondrion.
mitochondrial prohibitin complex A complex composed of two proteins, prohibitin 1 and prohibitin 2 (PHB1/PHB-1 and PHB2/PHB-2) that is highly conserved amongst eukaryotes and associated with the inner mitochondrial membrane. The mitochondrial prohibitin complex is a macromolecular supercomplex composed of repeating heterodimeric subunits of PHB1 and PHB2. The mitochondrial prohibitin complex plays a role in a number of biological processes, including mitochondrial biogenesis and function, development, replicative senescence, and cell death.
mitochondrial proton-transporting atp synthase complex A proton-transporting ATP synthase complex found in the mitochondrial membrane.
mitochondrial pyruvate dehydrogenase complex Complex that carries out the oxidative decarboxylation of pyruvate to form acetyl-CoA in eukaryotes; includes subunits possessing three catalytic activities: pyruvate dehydrogenase (E1), dihydrolipoamide S-acetyltransferase (E2), and dihydrolipoamide dehydrogenase (E3). The This Eukaryotic form usually contains more subunits than its bacterial counterpart; for example, one known complex contains 30 E1 dimers, 60 E2 monomers, and 6 E3 dimers as well as a few copies of pyruvate dehydrogenase kinase and pyruvate dehydrogenase phosphatase.
mitochondrial respiratory chain The protein complexes that form the mitochondrial electron transport system (the respiratory chain), associated with the inner mitochondrial membrane. The respiratory chain complexes transfer electrons from an electron donor to an electron acceptor and are associated with a proton pump to create a transmembrane electrochemical gradient.
mitochondrial respiratory chain complex i A protein complex located in the mitochondrial inner membrane that forms part of the mitochondrial respiratory chain. It contains about 25 different polypeptide subunits, including NADH dehydrogenase (ubiquinone), flavin mononucleotide and several different iron-sulfur clusters containing non-heme iron. The iron undergoes oxidation-reduction between Fe(II) and Fe(III), and catalyzes proton translocation linked to the oxidation of NADH by ubiquinone.
mitochondrial respiratory chain complex ii A protein complex located in the mitochondrial inner membrane that forms part of the mitochondrial respiratory chain. Contains the four polypeptide subunits of succinate dehydrogenase, flavin-adenine dinucleotide and iron-sulfur. Catalyzes the oxidation of succinate by ubiquinone. Connects the TCA cycle with the respiratory chain.
mitochondrial respiratory chain complex iii A protein complex located in the mitochondrial inner membrane that forms part of the mitochondrial respiratory chain. Contains about 10 polypeptide subunits including four redox centers: cytochrome b/b6, cytochrome c1 and an 2Fe-2S cluster. Catalyzes the oxidation of ubiquinol by oxidized cytochrome c1.
mitochondrial respiratory chain complex iv A protein complex located in the mitochondrial inner membrane that forms part of the mitochondrial respiratory chain. Contains the 13 polypeptide subunits of cytochrome c oxidase, including cytochrome a and cytochrome a3. Catalyzes the oxidation of reduced cytochrome c by dioxygen (O2).
mitochondrial respiratory chain supercomplex A set of respiratory enzyme complexes of the mitochondrial inner membrane (including, for example, Complex II, Complex III, Complex IV, or F1-F0 ATPase) arranged to form a large supercomplex.
mitochondrial ribonuclease p complex A ribonuclease P complex located in the mitochondrion of a eukaryotic cell, where it catalyzes the 5' endonucleolytic cleavage of precursor tRNAs to yield mature tRNAs. The subunit composition of mitochondrial ribonuclease P complexes varies between species, but the complex often contains a single RNA molecule and a single protein molecule.
mitochondrial ribosome A ribosome found in the mitochondrion of a eukaryotic cell; contains a characteristic set of proteins distinct from those of cytosolic ribosomes.
mitochondrial small ribosomal subunit The smaller of the two subunits of a mitochondrial ribosome.
mitochondrial sorting and assembly machinery complex A large complex of the mitochondrial outer membrane that mediates sorting of some imported proteins to the outer membrane and their assembly in the membrane; functions after import of incoming proteins by the mitochondrial outer membrane translocase complex.
mitochondrial tricarboxylic acid cycle enzyme complex Any of the heteromeric enzymes, located in the mitochondrion, that act in the tricarboxylic acid (TCA) cycle.
mitochondrion A semiautonomous, self replicating organelle that occurs in varying numbers, shapes, and sizes in the cytoplasm of virtually all eukaryotic cells. It is notably the site of tissue respiration.
mitosome A double-membrane-bounded organelle that functions in iron-sulfur protein maturation; evolutionarily derived from mitochondria. The mitosome has been detected only in anaerobic or microaerophilic organisms that do not have mitochondria, such as Entamoeba histolytica, Giardia intestinalis and several species of Microsporidia. These organisms are not capable of gaining energy from oxidative phosphorylation, which is normally performed by mitochondria.
mitotic checkpoint complex A multiprotein complex that functions as a mitotic checkpoint inhibitor of the anaphase-promoting complex/cyclosome (APC/C). In budding yeast this complex consists of Mad2p, Mad3p, Bub3p and Cdc20p, and in mammalian cells it consists of MAD2, BUBR1, BUB3, and CDC20.
mitotic cohesin complex A cohesin complex that mediates sister chromatid cohesion during mitosis; has a subunit composition distinct from that of the meiotic cohesin complex.
mitotic septin complex A heterooligomeric septin complex that acts during mitotic cell division.
mitotic spindle A spindle that forms as part of mitosis. Mitotic and meiotic spindles contain distinctive complements of proteins associated with microtubules.
mitotic spindle midzone The area in the center of the anaphase spindle consisting of microtubules, microtubule bundling factors and kinesin motors where the spindle microtubules from opposite poles overlap in an antiparallel manner.
mitotic spindle pole Either of the ends of a mitotic spindle, a spindle that forms as part of mitosis, where spindle microtubules are organized; usually contains a microtubule organizing center and accessory molecules, spindle microtubules and astral microtubules.
mitotic spindle pole body The microtubule organizing center on a spindle that forms as part of mitosis; functionally homologous to the animal cell centrosome.
mll1 complex A protein complex that can methylate lysine-4 of histone H3. MLL1/MLL is the catalytic methyltransferase subunit, and the complex also contains the core components ASH2L, HCFC1/HCF1 WDR5 and RBBP5.
mll1/2 complex A protein complex that can methylate lysine-4 of histone H3, and which contains either of the protein subunits MLL1 or MLL2 in human, or equivalent in other species.
mll3/4 complex A protein complex that can methylate lysine-4 of histone H3, and which contains either of the protein subunits MLL3 or MLL4 in mammals, or equivalent in other species.
mmxd complex A protein complex that contains the proteins MMS19, MIP18 and XPD, localizes to mitotic spindle during mitosis, and is required for proper chromosome segregation.
mon1-ccz1 complex A protein complex that functions as a guanine nucleotide exchange factor (GEF) and converts Rab-GDP to Rab-GTP. In S. cerevisiae, this complex consists of at least Mon1 and Ccz1, and serves as a GEF for the Rab Ypt7p.
monolayer-surrounded lipid storage body A subcellular organelle of plant cells surrounded by 'half-unit' or a monolayer membrane instead of the more usual bilayer. The storage body has a droplet of triglyceride surrounded by a monolayer of phospholipids, interacting with the triglycerides and the hydrophilic head groups facing the cytosol, and containing major protein components called oleosins.
monopolin complex A protein complex required for clamping microtubule binding sites, ensuring orientation of sister kinetochores to the same pole (mono-orientation) during meiosis I. In the yeast S. cerevisiae this complex consists of Csm1p, Lrs4p, Hrr25p and Mam1p; in S. pombe Psc1 and Mde4 have been identified as subunits.
mossy fiber rosette A synapse of a mossy fiber onto the dendrite of a granule cell; each mossy fiber can have up to 50 rosettes.
motile cilium A cilium which has a variable arrangement of axonemal microtubules, contains molecular motors, and beats with a characteristic whip-like pattern that promotes cell motility or transport of fluids and other cells across a cell surface. Motile cilia are typically found in multiple copies on epithelial cells that line the lumenal ducts of various tissues. Motile cilia may also function as sensory organelles.
motile primary cilium A primary cilium which may contain a variable array of axonemal microtubules and also contains molecular motors. Motile primary cilia display a distinct twirling motion that directs fluid flow asymmetrically across the cellular surface to affect asymmetric body plan organization.
moz/morf histone acetyltransferase complex A histone acetyltransferase complex that has histone H3 acetyltransferase and coactivator activities. Subunits of the human complex include MYST3/MOZ, MYST4/MORF, ING5, EAF6 and one of BRPF1, BRD1/BRPF2 and BRPF3.
mpf complex A complex consisting of a Cdc2-class (also known as Cdc28) cyclin-dependent kinase and an M-phase cyclin such as S. pombe Cdc13. The MPF complex phosphorylates and activates the anaphase promoting complex (APC).
mre11 complex Trimeric protein complex that possesses endonuclease activity; involved in meiotic recombination, DNA repair and checkpoint signaling. In Saccharomyces cerevisiae, the complex comprises Mre11p, Rad50p, and Xrs2p; complexes identified in other species generally contain proteins orthologous to the Saccharomyces cerevisiae proteins.
mrna cap binding complex Any protein complex that binds to an mRNA cap at any time in the lifetime of the mRNA.
mrna cap methyltransferase complex A protein complex that consists of an RNA 5' triphosphatase and a guanyl transferase (Cet1p and Ceg1p in S. cerevisiae; Pct1 and Ceg1 in S. pombe) and is involved in mRNA capping.
mrna cleavage and polyadenylation specificity factor complex A multisubunit complex that binds to the canonical AAUAAA hexamer and to U-rich upstream sequence elements on the pre-mRNA, thereby stimulating the otherwise weakly active and nonspecific polymerase to elongate efficiently RNAs containing a poly(A) signal.
mrna cleavage factor complex Any macromolecular complex involved in cleavage or polyadenylation of mRNA molecules.
mrna cleavage stimulating factor complex A protein complex required for mRNA cleavage but not for poly(A) addition.
mrna editing complex A protein complex that posttranscriptionally catalyzes insertion, deletion or substitution of nucleotides at multiple sites within nascent mRNA transcripts to produce mature mRNAs in eukaryotes.
msl complex A histone acetyltransferase complex that catalyzes the acetylation of a histone H4 lysine residue at position 16. In human, it contains the catalytic subunit MOF, and MSL1, MSL2 and MSL3.
mucocyst A small subcellular vesicle, surrounded by a membrane, in the pellicle of ciliate protozoans that discharges a mucus-like secretion.
mucus layer An extracellular region part that consists of a protective layer of mucus secreted by epithelial cells lining tubular organs of the body such as the colon or secreted into fluids such as saliva. Mucus is a viscous slimy secretion consisting of mucins (i.e. highly glycosylated mucin proteins) and various inorganic salts dissolved in water, with suspended epithelial cells and leukocytes.
multimeric ribonuclease p complex A ribonuclease P complex that generally contains a single RNA molecule and several protein molecules. Examples of this complex are found in Archaeal species.
multivesicular body A type of late endosome in which regions of the limiting endosomal membrane invaginate to form internal vesicles; membrane proteins that enter the internal vesicles are sequestered from the cytoplasm.
multivesicular body membrane The lipid bilayer surrounding a multivesicular body.
muscle cell projection A prolongation or process extending from a muscle cell. A muscle cell is a mature contractile cell, commonly known as a myocyte. This cell has as part of its cytoplasm myofibrils organized in various patterns.
muscle myosin complex A filament of myosin found in a muscle cell of any type.
muscle tendon junction A cell-substrate junction found at the terminal anchorage site of skeletal muscle cells to tendons.
mutlalpha complex A heterodimer involved in the recognition of base-base and small insertion/deletion mismatches. In human the complex consists of two subunits, MLH1 and PMS2.
mutlbeta complex A heterodimer involved in the recognition of base-base and small insertion/deletion mismatches. In human the complex consists of two subunits, MLH1 and PMS1.
mutsalpha complex A heterodimer involved in the recognition and repair of base-base and small insertion/deletion mismatches. In human the complex consists of two subunits, MSH2 and MSH6.
mutsbeta complex A heterodimer involved in binding to and correcting insertion/deletion mutations. In human the complex consists of two subunits, MSH2 and MSH3.
myb complex A multisubunit complex consisting of Myb and other proteins that regulates site specific DNA replication, gene amplification and transcriptional repression.
myelin sheath An electrically insulating fatty layer that surrounds the axons of many neurons. It is an outgrowth of glial cells: Schwann cells supply the myelin for peripheral neurons while oligodendrocytes supply it to those of the central nervous system.
myofibril The contractile element of skeletal and cardiac muscle; a long, highly organized bundle of actin, myosin, and other proteins that contracts by a sliding filament mechanism.
myofilament Any of the smallest contractile units of a myofibril (striated muscle fiber).
myosin complex A protein complex, formed of one or more myosin heavy chains plus associated light chains and other proteins, that functions as a molecular motor; uses the energy of ATP hydrolysis to move actin filaments or to move vesicles or other cargo on fixed actin filaments; has magnesium-ATPase activity and binds actin. Myosin classes are distinguished based on sequence features of the motor, or head, domain, but also have distinct tail regions that are believed to bind specific cargoes.
myosin filament A protein complex containing myosin heavy chains, plus associated light chains and other proteins, in which the myosin heavy chains are arranged into a filament.
myosin i complex A myosin complex containing a class I myosin heavy chain and associated light chains; myosin I heavy chains are single-headed, possess tails of various lengths, and do not self-associate into bipolar filaments; myosin I complexes are involved in diverse processes related to membrane traffic and cell movement.
myosin ii complex A myosin complex containing two class II myosin heavy chains, two myosin essential light chains and two myosin regulatory light chains. Also known as classical myosin or conventional myosin, the myosin II class includes the major muscle myosin of vertebrate and invertebrate muscle, and is characterized by alpha-helical coiled coil tails that self assemble to form a variety of filament structures.
myosin iv complex A myosin complex containing one or more class IV myosin heavy chains and associated light chains; myosin IV is relatively uncharacterized, but is predicted to have a single motor domain, one IQ motif and a tail with a Myosin Tail Homology (myTH4) domain homologous to that in the tails of myosins VII and XV.
myosin phosphatase complex An enzyme complex that catalyzes the removal of the phosphate group from phosphomyosin.
myosin v complex A myosin complex containing a dimer of class V myosin heavy chains and associated light chains; involved in intracellular transport. Myosin V is a dimeric molecule consisting of conserved motor domains followed by 6 IQ motifs which bind specific light chains and calmodulin. The tail domain is important for cellular localization and cargo binding and can be divided into an alpha-helical coiled coil region and a C-terminal globular region.
myosin vi complex A myosin complex containing one or more class VI myosin heavy chains and associated light chains. Myosin VI has a single IQ motif in the neck and a tail region with a coiled coil domain followed by a unique globular domain; a unique insertion that enables myosin VI to move towards the pointed or minus end of actin filaments.
myosin vii complex A myosin complex containing a dimer of class VII myosin heavy chains and associated light chains. Myosin VII (240 kDa) is predicted to be a dimeric molecule with 5 IQ motifs and a tail region with a short stretch of coiled coil followed by two myosin-tail homology (MyTH4) domains, two talin-binding (FERM) domains and an SH3-domain.
myosin viii complex A myosin complex containing a dimer of class VIII myosin heavy chains and associated light chains. Myosin VIII is predicted to be dimeric, and contain an unusual 100-190 residue N-terminal extension prior to their motor domains, 3-4 IQ motifs, a short region (~70 residues) of predicted alpha-helical coiled coil and a C-terminal domain.
myosin xi complex A myosin complex containing a dimer of class XI myosin heavy chains and associated light chains. Myosin XI heavy chain sizes are similar in molecular structure to the class V myosins with 5 to 6 IQ motifs and tail regions with predicted coiled coil domains (forming dimeric molecules) and large C-terminal regions.
myosin xiv complex A myosin complex containing a class XIV myosin heavy chain and associated light chains; myosin XIV heavy chains are the simplest known, containing a motor domain, no classic IQ motif and variable length tails.
myosin xviii complex A myosin complex containing a class XVIII myosin heavy chain and associated light chains; myosin XVIII heavy chains contain an N-terminal PDZ domain.
n-methyl-d-aspartate selective glutamate receptor complex An assembly of four or five subunits which form a structure with an extracellular N-terminus and a large loop that together form the ligand binding domain. The C-terminus is intracellular. The ionotropic glutamate receptor complex itself acts as a ligand gated ion channel; on binding glutamate, charged ions pass through a channel in the center of the receptor complex. NMDA receptors are composed of assemblies of NR1 subunits (Figure 3) and NR2 subunits, which can be one of four separate gene products (NR2A-D). Expression of both subunits are required to form functional channels. The glutamate binding domain is formed at the junction of NR1 and NR2 subunits. NMDA receptors are permeable to calcium ions as well as being permeable to other ions. Thus NMDA receptor activation leads to a calcium influx into the post-synaptic cells, a signal thought to be crucial for the induction of NMDA-receptor dependent LTP and LTD.
n-terminal protein acetyltransferase complex A complex that catalyzes the transfer of an acetyl group to the N-terminal residue of a protein acceptor molecule.
nadh dehydrogenase complex An integral membrane complex that possesses NADH oxidoreductase activity. The complex is one of the components of the electron transport chain. It catalyzes the transfer of a pair of electrons from NADH to a quinone.
nadph oxidase complex A enzyme complex of which the core is a heterodimer composed of a light (alpha) and heavy (beta) chain, and requires several other water-soluble proteins of cytosolic origin for activity. Functions in superoxide generation by the NADPH-dependent reduction of O2.
nascent polypeptide-associated complex A heterodimeric protein complex that can reversibly bind to ribosomes, and is located in direct proximity to newly synthesized polypeptide chains as they emerge from the ribosome.
nata complex A conserved complex that catalyzes the transfer of an acetyl group to an N-terminal Ser, Ala, Gly, or Thr residue of a protein acceptor molecule. In Saccharomyces the complex includes Nat1p and Ard1p, and may contain additional proteins.
natb complex A conserved complex that catalyzes the transfer of an acetyl group to the N-terminal residue of a protein acceptor molecule that has a Met-Glu, Met-Asp, Met-Asn, or Met-Met N-terminus. In Saccharomyces the complex includes Nat3p and Mdm20p.
natc complex A conserved complex that catalyzes the transfer of an acetyl group to the N-terminal residue of a protein acceptor molecule that has a Met-Ile, Met-Leu, Met-Trp, or Met-Phe N-terminus. In Saccharomyces the complex includes Mak3p, Mak10p, and Mak31p.
nbaf complex A SWI/SNF-type complex that is found in post-mitotic neurons, and in human contains actin and proteins encoded by the ARID1A/BAF250A or ARID1B/BAF250B, SMARCD1/BAF60A, SMARCD3/BAF60C, SMARCA2/BRM/BAF190B, SMARCA4/BRG1/BAF190A, SMARCB1/BAF47, SMARCC1/BAF155, SMARCE1/BAF57, SMARCC2/BAF170, DPF1/BAF45B, DPF3/BAF45C, ACTL6B/BAF53B genes. The nBAF complex along with CREST plays a role regulating the activity of genes essential for dendrite growth.
ndc80 complex A protein complex conserved among eukaryotes that forms part of the kinetochore and plays an essential role in forming stable kinetochore-microtubule attachments. The complex contains proteins known in several species, including budding and fission yeasts, as Ndc80p, Nuf2p, Spc24p, and Spc25p. In vertebrates it is part of the outer plate of the kinetochore.
nebenkern A product of the fusion of the mitochondria during spermatogenesis. After the completion of meiosis the mitochondria of the spermatid collect along side the nucleus and fuse into two masses; these wrap around each other to produce the spherical Nebenkern. During flagellum elongation the Nebenkern unfolds and the two derivatives (major and minor mitochondrial derivatives) elongate down the axoneme.
negative cofactor 2 complex A heterodimeric protein complex that can stably associate with TATA-binding protein on promoters, thereby preventing the assembly of transcription factors TFIIA and TFIIB and leading to repression of RNA polymerase II transcription. The two subunits, NC2alpha (Drap1) and NC2beta (Dr1), dimerize through histone fold domains of the H2A/H2B type present in the amino termini.
nelf complex A complex of five proteins, designated NELF-A, -B, -C, -D, and -E in human, that can physically associate with RNP polymerase II to induce transcriptional pausing.
nematocyst An organelle found in cnidoblast (nematoblast) cells. When matured, these stinging organelles store toxins and can deliver them when the cnidocil (a short extension of the cnidocyst) is stimulated by a prey or another stimulus.
nematosome Cytoplasmic, ball-like inclusion resembling a nucleolus and consisting of a convoluted network of electron-opaque strands embedded in a less dense matrix. It measures approximately 0.9 microns and lacks a limiting membrane. Its strands (diameter = 400-600 A) appear to be made of an entanglement of tightly packed filaments and particles approximately 25-50 A thick. Cytochemical studies suggest the presence of nonhistone proteins and some RNA. Usually only one such structure is present in a cell, and it appears to occur in most ganglion cells. Although they can be seen anywhere in the cell body, nematosomes are typically located in the perinuclear cytoplasm, where they are often associated with smooth-surfaced and coated vesicles.
nephrocyte diaphragm A specialized cell-cell junction found between nephrocytes of the insect kidney, which is adapted for filtration of hemolymph. The insect nephrocyte is anatomically and functionally similarity to the glomerular podocyte of vertebrates.
network-forming collagen trimer A collagen trimer that forms networks.
neurofilament A type of intermediate filament found in the core of neuronal axons. Neurofilaments are heteropolymers composed of three type IV polypeptides: NF-L, NF-M, and NF-H (for low, middle, and high molecular weight). Neurofilaments are responsible for the radial growth of an axon and determine axonal diameter.
neurofilament cytoskeleton Intermediate filament cytoskeletal structure that is made up of neurofilaments. Neurofilaments are specialized intermediate filaments found in neurons.
neuromuscular junction The junction between the axon of a motor neuron and a muscle fiber. In response to the arrival of action potentials, the presynaptic button releases molecules of neurotransmitters into the synaptic cleft. These diffuse across the cleft and transmit the signal to the postsynaptic membrane of the muscle fiber, leading to a change in post-synaptic potential.
neuron part Any constituent part of a neuron, the basic cellular unit of nervous tissue. A typical neuron consists of a cell body (often called the soma), an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the nervous system.
neuron projection A prolongation or process extending from a nerve cell, e.g. an axon or dendrite.
neuron projection membrane The portion of the plasma membrane surrounding a neuron projection.
neuron projection terminus The specialized, terminal region of a neuron projection such as an axon or a dendrite.
neuron spine A small membranous protrusion, often ending in a bulbous head and attached to the neuron by a narrow stalk or neck.
neuronal cell body The portion of a neuron that includes the nucleus, but excludes cell projections such as axons and dendrites.
neuronal ribonucleoprotein granule A ribonucleoprotein complex that is found in the cytoplasm of axons and dendrites, and transports translationally silenced mRNAs to dendritic synapses, where they are released and translated in response to specific exogenous stimuli.
neurosecretory vesicle A large cytoplasmic membrane-bounded vesicle with an electron dense granular core, up to 150-200 nm in diameter, found in neurosecretory cells in the hypothalamus.
new mitotic spindle pole body The spindle pole body that is formed by spindle pole body duplication, and to which proteins involved in mitotic exit signaling (for example, the septation initiation network in fission yeast) localize.
nexin complex A protein complex found in the axoneme of eukaryotic cilia and flagella. It forms interconnections between the microtubule outer doublets that surround the inner central pair of microtubules.
nf-kappab complex A protein complex that consists of a homo- or heterodimer of members of a family of structurally related proteins that contain a conserved N-terminal region called the Rel homology domain (RHD). In the nucleus, NF-kappaB complexes act as transcription factors. In unstimulated cells, NF-kappaB dimers are sequestered in the cytoplasm by IkappaB monomers; signals that induce NF-kappaB activity cause degradation of IkappaB, allowing NF-kappaB dimers to translocate to the nucleus and induce gene expression.
nf-kappab p50/p65 complex A heterodimer of NF-kappa B p50 and p65 subunits.
nitrate reductase complex An enzyme complex that catalyzes the formation of nitrate from nitrite with the concomitant reduction of an acceptor.
nitrogenase complex An enzyme complex composed of two proteins, dinitrogenase and nitrogenase reductase; dinitrogenase is tetrameric with an alpha2-beta2 structure and nitrogenase reductase is a homodimer, and both are associated with metal ions, which differ between species. Both proteins are required for the enzyme activity of the complex, the formation of oxidized ferredoxin and ammonia from reduced ferredoxin and nitrogen.
nlrp1 inflammasome complex A protein complex that consists of two components, NLRP1 (NALP1) and caspase-1 or caspase-5. The exact mechanisms of NLRP1 activation remain obscure, but potassium ion efflux appears to be essential.
nlrp3 inflammasome complex A protein complex that consists of three components, NLRP3 (NALP3), PYCARD and caspase-1. It is activated upon exposure to whole pathogens, as well as a number of structurally diverse pathogen- and danger-associated molecular patterns (PAMPs and DAMPs) and environmental irritants. Whole pathogens demonstrated to activate the NLRP3 inflammasome complex include the fungi Candida albicans and Saccharomyces cerevisiae, bacteria that produce pore-forming toxins, including Listeria monocytogenes and Staphylococcus aureus, and viruses such as Sendai virus, adenovirus, and influenza virus.
nms complex A supercomplex formed by the association of two subcomplexes (known as MIND and Ndc80 in Schizosaccharomyces) with additional proteins at the kinetochores of condensed nuclear chromosomes.
noc complex Any of several heterodimers containing one or two Noc proteins, associated with preribosomal complexes; involved in ribosome biogenesis.
noc4p-nop14p complex A heterodimer associated with precursors of the eukaryotic small ribosomal subunit, including the 90S preribosome; involved in small subunit biogenesis.
nodal receptor complex A protein complex containing at least a type II activin receptor, a type I activin receptor, and a coreceptor (EGF-CFC protein) such as Cripto or Cryptic. Nodal receptor complexes are capable of binding a nodal protein and transducing the signal into the cell.
node of ranvier An axon part that is a gap in the myelin where voltage-gated sodium channels cluster and saltatory conduction is executed.
non-growing cell tip A cell tip at which no growth takes place. For example, in fission yeast the cell end newly formed by cell division does not grow immediately upon its formation, and lacks actin cytoskeletal structures.
non-membrane-bounded organelle Organized structure of distinctive morphology and function, not bounded by a lipid bilayer membrane. Includes ribosomes, the cytoskeleton and chromosomes.
nonhomologous end joining complex A protein complex that plays a role in DNA double-strand break repair via nonhomologous end joining. Such complexes typically contain a specialized DNA ligase (e.g. Lig4 in eukaryotes) and one or more proteins that bind to DNA ends.
nonmotile primary cilium A primary cilium which contains a variable array of axonemal microtubules but does not contain molecular motors. Nonmotile primary cilia are found on many different cell types and function as sensory organelles that concentrate and organize sensory signaling molecules.
norc complex An ISWI complex that contains an ATPase subunit of the ISWI family (specifically SNF2H in mammals, which contain two ISWI homologs) and a Tip5 homolog. In mammals, NoRC is involved in regulation of transcription from RNAP I and RNA polymerase III promoters.
noxa-bcl-2 complex A heterodimeric protein complex consisting of NOXA and BCL-2, members of the Bcl-2 family of anti- and proapoptotic regulators.
npbaf complex A SWI/SNF-type complex that is found in neural stem or progenitor cells, and in human contains actin and proteins encoded by the ARID1A/BAF250A or ARID1B/BAF250B, SMARCD1/BAF60A, SMARCD3/BAF60C, SMARCA2/BRM/BAF190B, SMARCA4/BRG1/BAF190A, SMARCB1/BAF47, SMARCC1/BAF155, SMARCE1/BAF57, SMARCC2/BAF170, PHF10/BAF45A, ACTL6A/BAF53A genes. The npBAF complex is essential for the self-renewal/proliferative capacity of the multipotent neural stem cells.
nrd1 complex A complex that functions in transcription termination of RNA polymerase II transcribed non-coding RNAs. This complex interacts with the carboxy-terminal domain (CTD) of PolII and the terminator sequences in the nascent RNA transcript. In yeast this complex consists of Nrd1p, Nab3p, and Sen1p.
nsl complex A histone acetyltransferase complex that catalyzes the acetylation of a histone H4 lysine residues at several positions. In human, it contains the catalytic subunit MOF, NSL1/KIAA1267, NSL2/KANSL2, NSL3/KANSL3, MCRS1, PHF20, OGT1, WDR5 and HCF1.
nua3 histone acetyltransferase complex A Gcn5-independent multisubunit complex that catalyzes the acetylation of histone H3. The budding yeast complex includes Sas3p, Taf30p, and Yng1p.
nua4 histone acetyltransferase complex A complex having histone acetylase activity on chromatin, as well as ATPase, DNA helicase and structural DNA binding activities. The complex is thought to be involved in double-strand DNA break repair. Subunits of the human complex include HTATIP/TIP60, TRRAP, RUVBL1, BUVBL2, beta-actin and BAF53/ACTL6A. In yeast, the complex has 13 subunits, including the catalytic subunit Esa1 (homologous to human Tip60).
nuclear aryl hydrocarbon receptor complex An aryl hydrocarbon receptor (AhR) complex found in the nucleus; ; consists of ligand-bound AhR and the aryl hydrocarbon receptor nuclear translocator (ARNT).
nuclear body Extra-nucleolar nuclear domains usually visualized by confocal microscopy and fluorescent antibodies to specific proteins.
nuclear cap binding complex A conserved heterodimeric protein complex that binds to the 5' terminal cap structure m7G(5')ppp(5')N of nascent eukaryotic RNA polymerase II transcripts such as pre-mRNA and U snRNA. The consists of proteins known as CBP20 and CBP80, binds to cap structures in the nucleus, and is involved in pre-mRNA splicing, 3'-end formation, and RNA nuclear export.
nuclear chromatin The ordered and organized complex of DNA, protein, and sometimes RNA, that forms the chromosome in the nucleus.
nuclear chromosome A chromosome found in the nucleus of a eukaryotic cell.
nuclear chromosome part Any constituent part of a nuclear chromosome, a chromosome found in the nucleus of a eukaryotic cell.
nuclear chromosome, telomeric region The terminal region of a linear chromosome in the nucleus that includes the telomeric DNA repeats and associated proteins.
nuclear cohesin complex A cohesin complex required for cohesion between sister chromatids that remain in the nucleus.
nuclear condensin complex A multisubunit protein complex that plays a central role in the condensation of chromosomes that remain in the nucleus.
nuclear cyclin-dependent protein kinase holoenzyme complex Cyclin-dependent protein kinase (CDK) complex found in the nucleus.
nuclear dicing body A small round nuclear body, measuring 0.2-0.8 microns in diameter that is diffusely distributed throughout the nucleoplasm. Several proteins known to be involved in miRNA processing have been localized to these structures. D-bodies are thought to be involved in primary-miRNA processing and/or storage/assembly of miRNA processing complexes.
nuclear dna-directed rna polymerase complex A protein complex, located in the nucleus, that possesses DNA-directed RNA polymerase activity.
nuclear envelope The double lipid bilayer enclosing the nucleus and separating its contents from the rest of the cytoplasm; includes the intermembrane space, a gap of width 20-40 nm (also called the perinuclear space).
nuclear envelope lumen The region between the two lipid bilayers of the nuclear envelope; 20-40 nm wide.
nuclear euchromatin The dispersed less dense form of chromatin in the interphase nucleus. It exists in at least two forms, a some being in the form of transcriptionally active chromatin which is the least condensed, while the rest is inactive euchromatin which is more condensed than active chromatin but less condensed than heterochromatin.
nuclear heterochromatin A condensed form of chromatin, occurring in the nucleus during interphase, that stains strongly with basophilic dyes. The DNA of heterochromatin is typically replicated at a later stage in the cell-division cycle than euchromatin.
nuclear inclusion body An intranuclear focus at which aggregated proteins have been sequestered.
nuclear inner membrane The inner, i.e. lumen-facing, lipid bilayer of the nuclear envelope.
nuclear lamina The fibrous, electron-dense layer lying on the nucleoplasmic side of the inner membrane of a cell nucleus, composed of lamin filaments. The polypeptides of the lamina are thought to be concerned in the dissolution of the nuclear envelope and its re-formation during mitosis. The lamina is composed of lamin A and lamin C filaments cross-linked into an orthogonal lattice, which is attached via lamin B to the inner nuclear membrane through interactions with a lamin B receptor, an IFAP, in the membrane.
nuclear lumen The volume enclosed by the nuclear inner membrane.
nuclear matrix The dense fibrillar network lying on the inner side of the nuclear membrane.
nuclear membrane Either of the lipid bilayers that surround the nucleus and form the nuclear envelope; excludes the intermembrane space.
nuclear microtubule Any microtubule in the nucleus of a cell.
nuclear mis12/mind complex A multiprotein kinetochore subcomplex that binds to centromeric chromatin and forms part of the inner kinetochore of a chromosome in the nucleus. It helps to recruit outer kinetochore subunits that will bind to microtubules. Nuclear localization arises in some organisms because the nuclear envelope is not broken down during mitosis. In S. cerevisiae, it consists of at least four proteins: Mtw1p, Nnf1p, Nsl1p, and Dsn1.
nuclear origin of replication recognition complex A multisubunit complex that is located at the replication origins of a chromosome in the nucleus.
nuclear outer membrane The outer, i.e. cytoplasm-facing, lipid bilayer of the nuclear envelope; continuous with the endoplasmic reticulum of the cell and sometimes studded with ribosomes.
nuclear outer membrane-endoplasmic reticulum membrane network The continuous network of membranes encompassing the nuclear outer membrane and the endoplasmic reticulum membrane.
nuclear part Any constituent part of the nucleus, a membrane-bounded organelle of eukaryotic cells in which chromosomes are housed and replicated.
nuclear pericentric heterochromatin Nuclear heterochromatin that is located adjacent to the CENP-A rich centromere 'central core' and characterized by the modified histone H3K9me3.
nuclear periphery The portion of the nuclear lumen proximal to the inner nuclear membrane.
nuclear pore Any of the numerous similar discrete openings in the nuclear envelope of a eukaryotic cell, where the inner and outer nuclear membranes are joined.
nuclear pore central transport channel The central substructure of the nuclear pore complex (NPC), through which nucleocytoplasmic transport of RNAs, proteins and small molecules occurs. The central transport channel is filled with FG-nucleoporins, which form a selective barrier and provide a series of binding sites for transporter proteins. Characterized S. cerevisiae FG-nucleoporins include Nup159p, Nup145Np, Nup116p, Nup100p, Nsp1p, Nup57p, Nup49p, Nup42p, Nup53p, Nup59p/Asm4p, Nup60p and Nup1. Characterized vertebrate FG-nucleoporins include Nup214, Nup98, Nup62, Nup54, Nup58/45, NLP1, and Nup153.
nuclear pore linkers A substructure of the nuclear pore complex (NPC) that serves to connect members of the central transport channel (composed of FG-nucleoporins) to the core scaffold (composed of the inner and outer NPC rings). In S. cerevisiae, the linkers are Nic96p and Nup82p. In vertebrates, they are Nup93 and Nup88. Components are arranged in 8-fold symmetrical 'spokes' around the central transport channel. Both linkers can be isolated in association with specific FG-nucleoporins, complexes that are sometimes referred to as the Nic96 complex (Nic96p-Nsp1p-Nup49p-Nup57p) and the Nup82 complex (Nup82p-Nup116p-Nup159p-Gle2p).
nuclear pore outer ring A subcomplex of the nuclear pore complex (NPC) that forms the outer rings of the core scaffold, a lattice-like structure that gives the NPC its shape and strength. In S. cerevisiae, the two outer rings each contain multiple copies of the following proteins: Nup133p, Nup120p, Nup145Cp, Nup85p, Nup84p, Seh1p, and Sec13p. In vertebrates, the two outer rings each contain multiple copies of the following proteins: Nup133, Nup160, Nup96, Nup75, Nup107, Seh1, Sec13, Nup43, Nup37, and ALADIN. Components are arranged in 8-fold symmetrical 'spokes' around the central transport channel. A single 'spoke', can be isolated and is sometimes referred to as the Nup84 complex (S. cerevisiae) or the Nup107-160 complex (vertebrates).
nuclear pre-replicative complex A protein-DNA complex assembled at eukaryotic DNA replication origins during late mitosis and G1, allowing the origin to become competent, or 'licensed', for replication. The complex normally includes the origin recognition complex (ORC), Cdc6, Cdt1 and the MiniChromosome Maintenance (Mcm2-7) proteins.
nuclear proteasome complex A proteasome found in the nucleus of a cell.
nuclear replication fork The Y-shaped region of a nuclear replicating DNA molecule, resulting from the separation of the DNA strands and in which the synthesis of new strands takes place. Also includes associated protein complexes.
nuclear replisome A multi-component enzymatic machine at the nuclear replication fork, which mediates DNA replication. Includes DNA primase, one or more DNA polymerases, DNA helicases, and other proteins.
nuclear rna export factor complex A protein complex that contains two proteins (know in several organisms, including Drosophila, as NXF1 and NXF2) and is required for the export of the majority of mRNAs from the nucleus to the cytoplasm; localized in the nucleoplasm and at both the nucleoplasmic and cytoplasmic faces of the nuclear pore complex; shuttles between the nucleus and the cytoplasm.
nuclear rna-directed rna polymerase complex A complex required for RNAi mediated heterochromatin assembly. In S. pombe this contains RNA-directed RNA polymerase, a putative helicase and a protein containing a pap25 associated domain.
nuclear scf ubiquitin ligase complex A ubiquitin ligase complex, located in the nucleus, in which a cullin from the Cul1 subfamily and a RING domain protein form the catalytic core; substrate specificity is conferred by a Skp1 adaptor and an F-box protein. SCF complexes are involved in targeting proteins for degradation by the proteasome. The best characterized complexes are those from yeast and mammals (with core subunits named Cdc53/Cul1, Rbx1/Hrt1/Roc1).
nuclear speck A discrete extra-nucleolar subnuclear domain, 20-50 in number, in which splicing factors are seen to be localized by immunofluorescence microscopy.
nuclear stress granule A dense aggregation in the nucleus composed of proteins and RNAs that appear when the cell is under stress.
nuclear telomere cap complex A complex of DNA and protein located at the end of a linear chromosome in the nucleus that protects and stabilizes a linear chromosome.
nuclear transcription factor complex A protein complex, located in the nucleus, that is capable of associating with DNA by direct binding, or via other DNA-binding proteins or complexes, and regulating transcription.
nuclear transcriptional repressor complex A protein complex, located in the nucleus, that possesses activity that prevents or downregulates transcription.
nuclear ubiquitin ligase complex A ubiquitin ligase complex found in the nucleus.
nuclear viral factory A viral factory located in the nucleus of a host cell.
nucleocytoplasmic shuttling complex Any complex that acts to move proteins or RNAs into or out of the nucleus through nuclear pores.
nucleoid The region of a virus, bacterial cell, mitochondrion or chloroplast to which the nucleic acid is confined.
nucleolar chromatin The portion of nuclear chromatin associated with the nucleolus; includes the DNA encoding the ribosomal RNA.
nucleolar part Any constituent part of a nucleolus, a small, dense body one or more of which are present in the nucleus of eukaryotic cells. It is rich in RNA and protein, is not bounded by a limiting membrane, and is not seen during mitosis.
nucleolar preribosome Any complex of pre-rRNAs, ribosomal proteins, and associated proteins formed in the nucleolus during ribosome biogenesis.
nucleolus A small, dense body one or more of which are present in the nucleus of eukaryotic cells. It is rich in RNA and protein, is not bounded by a limiting membrane, and is not seen during mitosis. Its prime function is the transcription of the nucleolar DNA into 45S ribosomal-precursor RNA, the processing of this RNA into 5.8S, 18S, and 28S components of ribosomal RNA, and the association of these components with 5S RNA and proteins synthesized outside the nucleolus. This association results in the formation of ribonucleoprotein precursors; these pass into the cytoplasm and mature into the 40S and 60S subunits of the ribosome.
nucleolus organizer region A region of a chromosome where nucleoli form during interphase, and where genes encoding the largest rRNA precursor transcript are tandemly arrayed.
nucleolus-associated heterochromatin Dense particles of heterochromatin, consisting of a loosely twisted strand about 600 Angstrom thick, found associated with the nucleolus.
nucleomorph A small, vestigial nucleus found in some plastids that derive from a eukaryotic endosymbiont. Observed in chlorarachniophytes and cryptomonads, which acquired their plastids from a green and red alga respectively.
nucleoplasm That part of the nuclear content other than the chromosomes or the nucleolus.
nucleoplasm part Any constituent part of the nucleoplasm, that part of the nuclear content other than the chromosomes or the nucleolus.
nucleoplasmic reticulum Long, dynamic tubular channels, formed by invagination of the nuclear envelope, that extend deep into the nucleoplasm. The channels have an underlying lamina and are implicated in functioning in signaling and transport.
nucleosomal methylation activator complex A protein complex that contains eight subunits in common with the SWI/SNF complex, plus the ATPase BRG1 (SMARCA4) and the histone methyltransferase CARM1; the complex is involved in regulating nuclear receptor-dependent transcription.
nucleosome A complex comprised of DNA wound around a multisubunit core and associated proteins, which forms the primary packing unit of DNA into higher order structures.
nucleotide-excision repair complex Any complex formed of proteins that act in nucleotide-excision repair.
nucleotide-excision repair factor 1 complex One of several protein complexes involved in nucleotide-excision repair; possesses DNA damage recognition and endodeoxynuclease activities. In S. cerevisiae, it is composed of Rad1p, Rad10p, and Rad14p; in human the subunits are ERCC4/XPF, ERCC1 and XPA, respectively.
nucleotide-excision repair factor 2 complex One of several protein complexes involved in nucleotide-excision repair; possesses damaged DNA binding activity. In S. cerevisiae, it is composed of Rad4p and Rad23p.
nucleotide-excision repair factor 3 complex One of several protein complexes involved in nucleotide-excision repair; possesses endodeoxynuclease and DNA helicase activities. In S. cerevisiae, it is composed of Rad2p and the core TFIIH-Ssl2p complex (core TFIIH is composed of Rad3p, Tfb1p, Tfb2p, Ssl1p, Tfb4p and Tfb5p. Note that Ssl2p is also called Rad25p).
nucleotide-excision repair factor 4 complex One of several protein complexes involved in nucleotide-excision repair; possesses DNA damage recognition and DNA-dependent ATPase activities. In S. cerevisiae, it is composed of Rad7p and Rad16p.
nucleus A membrane-bounded organelle of eukaryotic cells in which chromosomes are housed and replicated. In most cells, the nucleus contains all of the cell's chromosomes except the organellar chromosomes, and is the site of RNA synthesis and processing. In some species, or in specialized cell types, RNA metabolism or DNA replication may be absent.
nucleus-vacuole junction An organelle membrane contact site formed between the vacuole membrane and the outer nuclear membrane. In S. cerevisiae these contacts are mediated through direct physical interaction between Vac8p and Nvj1p.
nurd complex An approximately 2 MDa multi-subunit complex that exhibits ATP-dependent chromatin remodeling activity in addition to histone deacetylase (HDAC) activity, and has been shown to establish transcriptional repression of a number of target genes in vertebrates, invertebrates and fungi. Amongst its subunits, the NuRD complex contains histone deacetylases, histone binding proteins and Mi-2-like proteins.
nurf complex An ISWI complex that contains an ATPase subunit of the ISWI family (SNF2L in mammals), a NURF301 homolog (BPTF in humans), and additional subunits, though the composition of these additional subunits varies slightly with species. NURF is involved in regulation of transcription from TRNA polymerase II promoters.
occluding junction A cell-cell junction that seals cells together in an epithelium in a way that prevents even small molecules from leaking from one side of the sheet to the other.
old mitotic spindle pole body The spindle pole body that exists in a cell prior to spindle pole body duplication. An old spindle pole body segregates to the daughter cell upon mitosis, and lacks active proteins involved in signaling exit from mitosis.
oligosaccharyltransferase complex A protein complex that is found in the endoplasmic reticulum membrane of eukaryotes and transfers lipid-linked oligosaccharide precursor to asparagine residues on nascent proteins. In yeast, the complex includes at least nine different subunits, whereas in mammalian cells at least three different forms of the complex have been detected.
omega speckle A nucleoplasmic speckle distributed in the interchromatin space of cells in close proximity to chromatin. Omega speckles are distinct from interchromatin granules and contain heterogeneous nuclear RNA-binding proteins (hnRNPs).
oncostatin-m receptor complex A heterodimeric receptor for the cytokine oncostatin-M (OSM). In humans the receptor complex is made up of the gene products gp130 and OSMR-beta.
oral apparatus Complex basket- or funnel-like structure used by the cell to collect food and channel it to the cytostome; includes specialized sub-structures made up of closely-spaced cilia and underlying basal bodies and fibrillar systems.
organellar large ribosomal subunit The larger of the two subunits of an organellar ribosome. Two sites on the ribosomal large subunit are involved in translation: the aminoacyl site (A site) and peptidyl site (P site).
organellar ribosome A ribosome contained within a subcellular membrane-bounded organelle.
organellar small ribosomal subunit The smaller of the two subunits of an organellar ribosome.
organelle Organized structure of distinctive morphology and function. Includes the nucleus, mitochondria, plastids, vacuoles, vesicles, ribosomes and the cytoskeleton, and prokaryotic structures such as anammoxosomes and pirellulosomes. Excludes the plasma membrane.
organelle envelope A double membrane structure enclosing an organelle, including two lipid bilayers and the region between them. In some cases, an organelle envelope may have more than two membranes.
organelle envelope lumen The region between the inner and outer lipid bilayers of an organelle envelope.
organelle inner membrane The inner, i.e. lumen-facing, lipid bilayer of an organelle envelope; usually highly selective to most ions and metabolites.
organelle lumen The internal volume enclosed by the membranes of a particular organelle; includes the volume enclosed by a single organelle membrane, e.g. endoplasmic reticulum lumen, or the volume enclosed by the innermost of the two lipid bilayers of an organelle envelope, e.g. nuclear lumen.
organelle membrane A membrane that is one of the two lipid bilayers of an organelle envelope or the outermost membrane of single membrane bound organelle.
organelle membrane contact site A zone of apposition between the membranes of two organelles, structured by bridging complexes. Membrane contact sites (MCSs) are specialized for communication, including the efficient traffic of small molecules such as Ca2+ ions and lipids, as well as enzyme-substrate interactions.
organelle outer membrane The outer, i.e. cytoplasm-facing in a cellular organelle, lipid bilayer of an organelle envelope.
organelle part Any constituent part of an organelle, an organized structure of distinctive morphology and function. Includes constituent parts of the nucleus, mitochondria, plastids, vacuoles, vesicles, ribosomes and the cytoskeleton, but excludes the plasma membrane.
organelle subcompartment A compartment that consists of a lumen and an enclosing membrane, and is part of an organelle.
organelle-enclosing lipid monolayer A lipid monolayer that surrounds and encloses an organelle.
origin recognition complex A multisubunit complex that is located at the replication origins of a chromosome.
orthogonal array Square array of closely spaced intramembrane particles, 4-6 nm in size, that form supramolecular aggregates found in the plasma membrane of astrocytes, skeletal muscle and epithelial cells. They have been shown to contain aquaporins (water channels).
osmiophilic body A membrane-bounded vesicle found predominantly in Plasmodium female gametocytes, that becomes progressively more abundant as the gametocyte reaches full maturity. These vesicles lie beneath the subpellicular membrane of the gametocyte, and the release of their contents into the parasitophorous vacuole has been postulated to aid in the escape of gametocytes from the erythrocyte after ingestion by the mosquito.
ost-alpha/ost-beta complex A heterodimeric protein complex composed of Ost-alpha/SLC51A and Ost-beta/SLC51B subunits and involved in bile acid transport activity.
other organism A secondary organism with which the first organism is interacting.
other organism cell A cell of a secondary organism with which the first organism is interacting.
other organism cell membrane The cell membrane of a secondary organism with which the first organism is interacting.
other organism membrane A membrane of a secondary organism with which the first organism is interacting.
other organism part Any constituent part of a secondary organism with which the first organism is interacting.
other organism postsynaptic membrane A postsynaptic membrane that is part of another organism, i.e. a secondary organism with which the first organism is interacting. A postsynaptic membrane is a specialized area of membrane facing the presynaptic membrane on the tip of the nerve ending and separated from it by a minute cleft (the synaptic cleft). Neurotransmitters transmit the signal across the synaptic cleft to the postsynaptic membrane.
other organism presynaptic membrane A presynaptic membrane that is part of another organism, i.e. a secondary organism with which the first organism is interacting. A presynaptic membrane is specialized area of membrane of the axon terminal that faces the plasma membrane of the neuron or muscle fiber with which the axon terminal establishes a synaptic junction; many synaptic junctions exhibit structural presynaptic characteristics, such as conical, electron-dense internal protrusions, that distinguish it from the remainder of the axon plasma membrane.
outer acrosomal membrane The acrosomal membrane region that underlies the plasma membrane of the sperm. This membrane fuses with the sperm plasma membrane as part of the acrosome reaction.
outer dense fiber Structure or material found in the flagella of mammalian sperm that surrounds each of the nine microtubule doublets, giving a 9 + 9 + 2 arrangement rather than the 9 + 2 pattern usually seen. These dense fibers are stiff and noncontractile.
outer dynein arm Outer arm structure present on the outer doublet microtubules of ciliary and flagellar axonemes. Outer dynein arms contain 2-3 heavy chains, two or more intermediate chains and a cluster of 4-8 light chains. Inner and outer dynein arms have different functions in the generation of microtubule-based motility.
outer endospore membrane The outer membrane around a bacterial endospore, located between the endospore cortex and endospore coat.
outer membrane The external membrane of Gram-negative bacteria or certain organelles such as mitochondria and chloroplasts; freely permeable to most ions and metabolites.
outer mucus layer The outer of two mucus layers secreted by epithelial cells in the colon; the outer mucus layer is loosely packed and can be colonized by bacteria.
oxidoreductase complex Any protein complex that possesses oxidoreductase activity.
oxoglutarate dehydrogenase complex A complex of multiple copies of three enzymatic components: oxoglutarate dehydrogenase (lipoamide) ; EC:1.2.4.2 (E1), dihydrolipoamide S-succinyltransferase ; EC:2.3.1.61 (E2) and dihydrolipoamide dehydrogenase ; EC:1.8.1.4 (E3); catalyzes the overall conversion of 2-oxoglutarate to succinyl-CoA and carbon dioxide (CO2).
p granule A small cytoplasmic, non-membranous RNA/protein complex aggregates in the primordial germ cells of many higher eukaryotes.
pairing center A special chromosome region located towards one end of a chromosome that contains dispersed copies of short, repetitive DNA sequences and functions as a cis-acting element essential for presynaptic homologous chromosome pairing and chromosome-nuclear envelope attachment.
palmitoyltransferase complex A protein complex with palmitoyltransferase activity.
pan complex A complex that possesses poly(A)-specific ribonuclease activity; catalyzes the message-specific shortening of mRNA poly(A) tails. Contains at least two subunits, known as Pan2p and Pan3p in Saccharomyces.
paraferritin complex A cytoplasmic protein complex that contains integrin, mobilferrin and a flavin monooxygenase, is capable of reducing Fe(III) to Fe(II) utilizing NADPH, and is involved in iron transport. Fe(II) is required in the cell as the substrate for ferrochelatase in the synthesis of heme.
parallel fiber A parallel fiber results from the bifurcation of a cerebellar granule cell axon in the molecular layer into two diametrically opposed branches, that are oriented parallel to the long axis of the folium.
paranodal junction A highly specialized cell-cell junction found in vertebrates, which forms between a neuron and a glial cell, and has structural similarity to Drosophila septate junctions. It flanks the node of Ranvier in myelinated nerve and electrically isolates the myelinated from unmyelinated nerve segments and physically separates the voltage-gated sodium channels at the node from the cluster of potassium channels underneath the myelin sheath.
paranode region of axon An axon part that is located adjacent to the nodes of Ranvier and surrounded by lateral loop portions of myelin sheath.
paraspeckles Discrete subnuclear bodies in the interchromatin nucleoplasmic space, often located adjacent to nuclear specks. 10-20 paraspeckles are typically found in human cell nuclei.
pas complex A class III phosphatidylinositol 3-kinase complex that contains a phosphatidylinositol-3-phosphate 5-kinase subunit (Fab1p in yeast; PIKfyve in mammals), a kinase activator, and a phosphatase, and may also contain additional proteins; it is involved in regulating the synthesis and turnover of phosphatidylinositol 3,5-bisphosphate. In mammals the complex is composed of PIKFYVE, FIG4 and VAC14. In yeast it is composed of Atg18p, Fig4p, Fab1p, Vac14p and Vac7p.
pbaf complex A SWI/SNF-type complex that contains the ATPase product of the mammalian BAF180 gene.
pcaf complex A large multiprotein complex that possesses histone acetyltransferase activity and is involved in regulation of transcription. The composition is similar to that of the SAGA complex, but includes fewer Spt and Ada proteins, and more TAFs.
pcg protein complex A chromatin-associated multiprotein complex containing Polycomb Group proteins. In Drosophila, Polycomb group proteins are involved in the long-term maintenance of gene repression, and PcG protein complexes associate with Polycomb group response elements (PREs) in target genes to regulate higher-order chromatin structure.
pcna complex A protein complex composed of three identical PCNA monomers, each comprising two similar domains, which are joined in a head-to-tail arrangement to form a homotrimer. Forms a ring-like structure in solution, with a central hole sufficiently large to accommodate the double helix of DNA. Originally characterized as a DNA sliding clamp for replicative DNA polymerases and as an essential component of the replisome, and has also been shown to be involved in other processes including Okazaki fragment processing, DNA repair, translesion DNA synthesis, DNA methylation, chromatin remodeling and cell cycle regulation.
pcna-p21 complex A protein complex that contains the cyclin-dependent protein kinase inhibitor p21WAF1/CIP1 bound to PCNA; formation of the complex inhibits DNA replication.
pdx1-pbx1b-mrg1 complex A protein complex that contains the homeodomain proteins PDX1, PBX1b and MRG1 (MEIS2) and is involved in the transcriptional regulation of pancreatic acinar cell-specific genes.
pebow complex A protein complex that is involved in coordinating ribosome biogenesis with cell cycle progression. In human, it is composed of Pes1, Bop1, and WDR12; in Saccharomyces the proteins are known as Nop7p, Erb1 and Ytm1 respectively.
pectic matrix The gel-like pectin matrix consists of the interlinked acidic and neutral pectin networks that are further cross-linked by calcium bridges. Pectins consist largely of long chains of mostly galacturonic acid units (typically 1,4 linkages and sometimes methyl esters). Three major pectic polysaccharides (homogalacturonan, rhamnogalacturonan I and rhamnogalacturonan II) are thought to occur in all primary cell walls.
pellicle The structure enclosing an apicomplexan parasite cell; consists of the cell membrane with its associated infrastructure of microtubules, microfilaments and other organelles.
peribacteroid fluid The soluble material inside the peribacteroid membrane, but outside of the bacteroid, within a bacteroid-containing symbiosome.
peribacteroid membrane A membrane that surrounds one or more bacteroids (such as nitrogen-fixing bacteroids within legume root nodule cells).
pericanalicular vesicle A membrane-bounded vesicle found near the apical, or pericanalicular, membrane of a hepatocyte; contains proteins involved in bile salt transport and other fluid and solute transport processes.
pericellular basket Ramification of basket cell axon surrounding cell bodies, forming the characteristic pericellular baskets from which the cell class derives its name.
pericentric heterochromatin Heterochromatin that is located adjacent to the CENP-A rich centromere 'central core' and characterized by the modified histone H3K9me3.
pericentriolar material A network of small fibers that surrounds the centrioles in cells; contains the microtubule nucleating activity of the centrosome.
perichromatin fibrils Structures of variable diameter visible in the nucleoplasm by electron microscopy, mainly observed near the border of condensed chromatin. The fibrils are enriched in RNA, and are believed to be sites of pre-mRNA splicing and polyadenylylation representing the in situ form of nascent transcripts.
perikaryon The portion of the cell soma (cell body) that excludes the nucleus.
perineuronal net A dense extracellular matrix (ECM) structure that forms around many neuronal cell bodies and dendrites late in development and is responsible for synaptic stabilization in the adult brain.
perinuclear endoplasmic reticulum The portion of endoplasmic reticulum, the intracellular network of tubules and cisternae, that occurs near the nucleus. The lumen of the perinuclear endoplasmic reticulum is contiguous with the nuclear envelope lumen (also called perinuclear space), the region between the inner and outer nuclear membranes.
perinuclear region of cytoplasm Cytoplasm situated near, or occurring around, the nucleus.
perinuclear theca A condensed cytoplasmic structure that covers the nucleus of mammalian spermatozoa except for a narrow zone around the insertion of the tail. It shows two distinct regions, a subacrosomal layer and, continuing caudally beyond the acrosomic system, the postacrosomal sheath. The perinuclear theca has been considered a cytoskeletal scaffold responsible for maintaining the overall architecture of the mature sperm head; however, recent studies indicate that the bulk of its constituent proteins are not traditional cytoskeletal proteins but rather a variety of cytosolic proteins.
perinucleolar compartment The perinucleolar compartment (PNC) is a subnuclear structure associated with, but structurally distinct from, the nucleolus. The PNC contains large amounts of the heterogeneous nuclear ribonucleoprotein complex (hnRNP) called hnRNP 1 (PTB). Many RNA binding proteins as well as RNA polymerase III transcripts are highly enriched in this compartment. PTB and pol III transcripts are required for the integrity of the PNC.
periplasmic flagellum Flagellar filaments located in the periplasmic space; characterized in spirochetes, in which they are essential for shape and motility. Composed of a core surrounded by two sheath layers, the flagella rotate to allow migration of the cell through viscous media, which would not be possible using external flagella.
periplasmic space The region between the inner (cytoplasmic) and outer membrane (Gram-negative Bacteria) or cytoplasmic membrane and cell wall (Fungi and Gram-positive Bacteria).
peroxisomal matrix The volume contained within the membranes of a peroxisome; in many cells the matrix contains a crystalloid core largely composed of urate oxidase.
peroxisomal membrane The lipid bilayer surrounding a peroxisome.
peroxisomal part Any constituent part of a peroxisome, a small, membrane-bounded organelle that uses dioxygen (O2) to oxidize organic molecules; contains some enzymes that produce and others that degrade hydrogen peroxide (H2O2).
peroxisome A small organelle enclosed by a single membrane, and found in most eukaryotic cells. Contains peroxidases and other enzymes involved in a variety of metabolic processes including free radical detoxification, lipid catabolism and biosynthesis, and hydrogen peroxide metabolism.
pha granule An inclusion body located in the cytoplasm that consists of polyhydroxyalkanoate (PHA) molecules and associated proteins, surrounded by a phospholipid monolayer; the proteins include PHA synthase, PHA depolymerase and 3HB-oligomer hydroxylase, phasins (PhaPs), which are thought to be the major structural proteins of the membrane surrounding the inclusion, and the regulator of phasin expression PhaR.
phagocytic cup An invagination of the cell membrane formed by an actin dependent process during phagocytosis. Following internalization it is converted into a phagosome.
phagocytic vesicle A membrane-bounded intracellular vesicle that arises from the ingestion of particulate material by phagocytosis.
phagocytic vesicle membrane The lipid bilayer surrounding a phagocytic vesicle.
phagolysosome A membrane-bounded intracellular vesicle formed by maturation of an early phagosome following the ingestion of particulate material by phagocytosis; during maturation, phagosomes acquire markers of late endosomes and lysosomes.
phagolysosome membrane The lipid bilayer surrounding a phagolysosome.
phosphatase complex A protein complex which is capable of phosphatase activity.
phosphatidylinositol 3-kinase complex A protein complex capable of phosphatidylinositol 3-kinase activity and containing subunits of any phosphatidylinositol 3-kinase (PI3K) enzyme. These complexes are divided in three classes (called I, II and III) that differ for their presence across taxonomic groups and for the type of their constituents. Catalytic subunits of phosphatidylinositol 3-kinase enzymes are present in all 3 classes; regulatory subunits of phosphatidylinositol 3-kinase enzymes are present in classes I and III; adaptor proteins have been observed in class II complexes and may be present in other classes too.
phosphatidylinositol 3-kinase complex, class i A phosphatidylinositol 3-kinase complex that contains a catalytic and a regulatory subunit of a phosphatidylinositol 3-kinase (PI3K) enzyme, plus one or more adaptor proteins. Class I PI3Ks phosphorylate phosphatidylinositol [PI], phosphatidylinositol-4-phosphate [PI(4)P] and phosphatidylinositol-4,5-bisphosphate [PI(4,5)P2], and are divided into subclasses A and B according to the type of adaptor subunit with which they associate. The class I PI3K subfamily of genes comprises members in vertebrates, worm and fly, but none in yeast.
phosphatidylinositol 3-kinase complex, class ia A class I phosphatidylinositol 3-kinase complex that possesses 1-phosphatidylinositol-4-phosphate 3-kinase activity; comprises a catalytic class IA phosphoinositide 3-kinase (PI3K) subunit and an associated SH2 domain-containing regulatory subunit that is a member of a family of related proteins often called p85 proteins. Through the interaction with the SH2-containing adaptor subunits, Class IA PI3K catalytic subunits are linked to tyrosine kinase signaling pathways.
phosphatidylinositol 3-kinase complex, class ib A class I phosphatidylinositol 3-kinase complex that possesses 1-phosphatidylinositol-4-phosphate 3-kinase activity; comprises a catalytic class IB phosphoinositide 3-kinase (PI3K) subunit and an associated regulatory subunit that is larger than, and unrelated to, the p85 proteins present in class IA complexes. Class IB PI3Ks are stimulated by G-proteins and do not interact with the SH2-domain containing adaptors that bind to Class IA PI3Ks.
phosphatidylinositol 3-kinase complex, class iii A phosphatidylinositol 3-kinase complex that contains a catalytic class III phosphoinositide 3-kinase (PI3K) subunit bound to a regulatory (adaptor) subunit. Additional adaptor proteins may be present. Class III PI3Ks have a substrate specificity restricted to phosphatidylinositol (PI).
phosphatidylinositol 3-kinase complex, class iii, type i A class III phosphatidylinositol 3-kinase complex that is involved in autophagy. In budding yeast, this complex consists of Vps30p, Vps34p, Apg14p and Vps15p.
phosphatidylinositol 3-kinase complex, class iii, type ii A class III phosphatidylinositol 3-kinase complex that is involved in vacuolar protein sorting (VPS) via endosomes. In budding yeast, this complex consists of Vps30p, Vps34p, Vps38 and Vps15p.
phosphorylase kinase complex An enzyme complex that catalyzes the phosphorylation of phosphorylase b to form phosphorylase a.
photoreceptor connecting cilium A nonmotile primary cilium that has a 9+0 microtubule array and forms the portion of the axoneme traversing the boundary between the photoreceptor inner and outer segments.
photoreceptor disc membrane Ovally-shaped membranous stack located inside the photoreceptor outer segment, and containing densely packed molecules of the photoreceptor protein rhodopsin that traverse the lipid bilayer. Disc membranes are apparently derived from the plasma membrane in the region of the cilium that connects the photoreceptor outer segment to the inner segment.
photoreceptor inner segment The inner segment of a vertebrate photoreceptor containing mitochondria, ribosomes and membranes where opsin molecules are assembled and passed to be part of the outer segment discs.
photoreceptor inner segment membrane The membrane surrounding the outer segment of a vertebrate photoreceptor. The photoreceptor inner segment contains mitochondria, ribosomes and membranes where opsin molecules are assembled and passed to be part of the outer segment discs.
photoreceptor outer segment The outer segment of a vertebrate photoreceptor that contains discs of photoreceptive membranes.
photoreceptor outer segment membrane The membrane surrounding the outer segment of a vertebrate photoreceptor.
photosynthetic membrane A membrane enriched in complexes formed of reaction centers, accessory pigments and electron carriers, in which photosynthetic reactions take place.
photosystem A complex located in a photosynthetic membrane that consists of a photoreaction center associated with accessory pigments and electron carriers. Examples of this component are found in Arabidopsis thaliana and in photosynthetic bacterial and archaeal species.
photosystem i A photosystem that contains an iron-sulfur reaction center associated with accessory pigments and electron carriers. In cyanobacteria and chloroplasts, photosystem I functions as a light-dependent plastocyanin-ferredoxin oxidoreductase, transferring electrons from plastocyanin to ferredoxin; in photosynthetic bacteria that have only a single type I photosystem, such as the green sulfur bacteria, electrons can go either to ferredoxin (Fd) -> NAD+ or to menaquinone (MK) -> Cytb/FeS -> Cytc555 -> photosystem I (cyclic photophosphorylation).
photosystem i antenna complex The antenna complex of photosystem I. A photosystem has two closely linked components, an antenna containing light-absorbing pigments and a reaction center. Each antenna contains one or more light-harvesting complexes (LHCs).
photosystem i reaction center A photochemical system containing P700, the chlorophyll a dimer that functions as a primary electron donor. Functioning as a light-dependent plastocyanin-ferredoxin oxidoreductase, it transfers electrons from plastocyanin to ferredoxin.
photosystem ii A photosystem that contains a pheophytin-quinone reaction center with associated accessory pigments and electron carriers. In cyanobacteria and chloroplasts, in the presence of light, PSII functions as a water-plastoquinone oxidoreductase, transferring electrons from water to plastoquinone, whereas other photosynthetic bacteria carry out anoxygenic photosynthesis and oxidize other compounds to re-reduce the photoreaction center.
photosystem ii antenna complex The antenna complex of photosystem II. A photosystem has two closely linked components, an antenna containing light-absorbing pigments and a reaction center. Each antenna contains one or more light-harvesting complexes (LHCs).
photosystem ii oxygen evolving complex A complex, composed of a cluster of manganese, calcium and chloride ions bound to extrinsic proteins, that catalyzes the splitting of water to O2 and 4 H+. In cyanobacteria there are five extrinsic proteins in OEC (PsbO, PsbP-like, PsbQ-like, PsbU and PsbV), while in plants there are only three (PsbO, PsbP and PsbQ).
photosystem ii reaction center An integral membrane complex containing P680, the chlorophyll a molecule that functions as a primary electron donor. In the light, functioning as a water-plastoquinone oxidoreductase, it transfers electrons from water to plastoquinone.
phragmoplast Fibrous structure (light microscope view) that arises between the daughter nuclei at telophase and within which the initial partition (cell plate), dividing the mother cell in two (cytokinesis), is formed. Appears at first as a spindle connected to the two nuclei, but later spreads laterally in the form of a ring. Consists of microtubules.
phragmosome A flattened membranous vesicle containing cell wall components.
phycobilisome Any of the granules, approximately 32 nm x 48 nm and consisting of highly aggregated phycobiliproteins, that are attached in arrays to the external face of a thylakoid membrane in algae of the phyla Cyanophyta and Rhodophyta, where they function as light-harvesting devices in photosynthesis. Excitation energy in the phycobilisome flows in the sequence: phycoerythrin, phycocyanin, allophycocyanin before passing to the antenna chlorophyll of photosystem II.
pi-body A P granule that contains the PIWIL2-TDRD1 module, a set of proteins that act in the primary piRNA pathway. The pi-body corresponds to the cementing material between mitochondria found in gonocytes.
piccolo nua4 histone acetyltransferase complex A heterotrimeric H4/H2A histone acetyltransferase complex with a substrate preference of chromatin over free histones. It contains a subset of the proteins found in the larger NuA4 histone acetyltransferase complex; for example, the S. cerevisiae complex contains Esa1p, Yng2p, and Epl1p.
pick body Cellular inclusion composed of numerous tau fibrils arranged in a disorderly array. Tau protein is a major component, though Pick bodies also contain ubiquitin, alpha-synuclein, and apolipoprotein E.
pigment granule A small, subcellular membrane-bounded vesicle containing pigment and/or pigment precursor molecules. Pigment granule biogenesis is poorly understood, as pigment granules are derived from multiple sources including the endoplasmic reticulum, coated vesicles, lysosomes, and endosomes.
pilus A proteinaceous hair-like appendage on the surface of bacteria ranging from 2-8 nm in diameter.
pilus part Any constituent part of a pilus, a proteinaceous hair-like appendage on the surface of bacteria ranging from 2-8 nm in diameter.
pilus shaft The long, slender, mid section of a pilus.
pilus tip The pointed extremity furthest from the cell of a pilus.
pinosome A membrane-bounded, uncoated intracellular vesicle formed by the process of pinocytosis.
pip-body A P granule that contains the PIWIL4-TDRD9 module, a set of proteins that act in the secondary piRNA pathway.
plant cell papilla A cell projection that is a short, rounded projection from a plant epidermal cell.
plant-type cell wall A more or less rigid stucture lying outside the cell membrane of a cell and composed of cellulose and pectin and other organic and inorganic substances.
plant-type vacuole A closed structure that is completely surrounded by a unit membrane, contains liquid, and retains the same shape regardless of cell cycle phase. An example of this structure is found in Arabidopsis thaliana.
plant-type vacuole membrane The lipid bilayer surrounding a vacuole that retains the same shape regardless of cell cycle phase. The membrane separates its contents from the cytoplasm of the cell. An example of this component is found in Arabidopsis thaliana.
plasma lipoprotein particle A spherical particle with a hydrophobic core of triglycerides and/or cholesterol esters, surrounded by an amphipathic monolayer of phospholipids, cholesterol and apolipoproteins. Plasma lipoprotein particles transport lipids, which are non-covalently associated with the particles, in the blood or lymph.
plasma membrane The membrane surrounding a cell that separates the cell from its external environment. It consists of a phospholipid bilayer and associated proteins.
plasma membrane light-harvesting complex A plasma membrane protein-pigment complex that may be closely or peripherally associated to photosynthetic reaction centers that participate in harvesting and transferring radiant energy to the reaction center. Examples of this complex are found in bacterial species.
plasma membrane part Any constituent part of the plasma membrane, the membrane surrounding a cell that separates the cell from its external environment. It consists of a phospholipid bilayer and associated proteins.
plasma membrane raft A membrane raft that is part of the plasma membrane.
plasma membrane region A membrane that is a (regional) part of the plasma membrane.
plasma membrane respiratory chain A respiratory chain located in the plasma membrane of a cell; made up of the protein complexes that form the electron transport system (the respiratory chain), associated with the plasma membrane. The respiratory chain complexes transfer electrons from an electron donor to an electron acceptor and are associated with a proton pump to create a transmembrane electrochemical gradient.
plasma membrane-derived chromatophore A pigment-bearing structure that is derived from the cytoplasmic membrane, sometimes consisting of simple invaginations and sometimes a complete vesicle. This component is found in certain photosynthetic bacteria and cyanobacteria.
plasma membrane-derived chromatophore membrane The lipid bilayer associated with a plasma membrane-derived chromatophore; surrounds chromatophores that form complete vesicles.
plasmodesma A fine cytoplasmic channel, found in all higher plants, that connects the cytoplasm of one cell to that of an adjacent cell.
plastid Any member of a family of organelles found in the cytoplasm of plants and some protists, which are membrane-bounded and contain DNA. Plant plastids develop from a common type, the proplastid.
plastid acetyl-coa carboxylase complex An acetyl-CoA carboxylase complex located in the stroma of a plastid.
plastid chromosome A circular DNA molecule containing plastid encoded genes.
plastid envelope The double lipid bilayer enclosing a plastid and separating its contents from the rest of the cytoplasm; includes the intermembrane space.
plastid inner membrane The inner, i.e. lumen-facing, lipid bilayer of the plastid envelope; also faces the plastid stroma.
plastid intermembrane space The region between the inner and outer lipid bilayers of the plastid envelope.
plastid large ribosomal subunit The larger of the two subunits of a plastid ribosome. Two sites on the ribosomal large subunit are involved in translation: the aminoacyl site (A site) and peptidyl site (P site).
plastid membrane Either of the lipid bilayers that surround a plastid and form the plastid envelope.
plastid nucleoid The region of a plastid to which the DNA is confined.
plastid outer membrane The outer, i.e. cytoplasm-facing, lipid bilayer of the plastid envelope.
plastid part Any constituent part of a plastid, a member of a family of organelles found in the cytoplasm of plants and some protists, which are membrane-bounded and contain DNA. Plant plastids develop from a common type, the proplastid.
plastid pyruvate dehydrogenase complex Complex that carries out the oxidative decarboxylation of pyruvate to form acetyl-CoA; comprises subunits possessing three catalytic activities: pyruvate dehydrogenase (E1), dihydrolipoamide S-acetyltransferase (E2), and dihydrolipoamide dehydrogenase (E3). This complex is found in plant plastids and is distinct from the one found in mitochondria.
plastid ribosome A ribosome contained within a plastid.
plastid small ribosomal subunit The smaller of the two subunits of a plastid ribosome.
plastid stroma The proteinaceous ground substance of plastids.
plastid thylakoid Any thylakoid within a plastid.
plastid thylakoid lumen The volume enclosed by a plastid thylakoid membrane.
plastid thylakoid membrane The lipid bilayer membrane of any thylakoid within a plastid.
plastid-encoded plastid rna polymerase complex An RNA polymerase complex containing polypeptides encoded by the plastid genome. Plastid-encoded DNA-directed RNA polymerases resemble eubacterial multisubunit RNA polymerases, with a core composed of alpha, beta, and beta-prime subunits. Some forms contain multiple additional subunits. An additional sigma factor subunit is required for promoter recognition.
plastid-encoded plastid rna polymerase complex a A plastid-encoded DNA-directed RNA polymerase complex that resembles eubacterial multisubunit RNA polymerases, with a core composed of alpha, beta, and beta-prime subunits. An additional subunit, a sigma factor, is required for promoter recognition. PEP-A is generated from the PEP-B form during chloroplast maturation to generate a complex composed of at least thirteen polypeptides that is not sensitive to the antibiotic rifampicin, like its precursor form the PEP-B complex.
plastid-encoded plastid rna polymerase complex b A plastid-encoded DNA-directed RNA polymerase complex that resembles eubacterial multisubunit RNA polymerases with a core composed of alpha, beta, and beta-prime subunits. An additional subunit, a sigma factor, is required for promoter recognition. PEP-B is distinguished from PEP-A by its sensitivity to the antibiotic rifampicin. PEP-B is found in both etioplasts and chloroplasts, but is the predominate form in etioplasts. It forms the core of the PEP-A form; the conversion from PEP-B to PEP-A occurs during chloroplast maturation.
plastoglobule A lipoprotein particle present in chloroplasts. They are rich in non-polar lipids (triglycerides, esters) as well as in prenylquinones, plastoquinone and tocopherols. Plastoglobules are often associated with thylakoid membranes, suggesting an exchange of lipids with thylakoids.
platelet alpha granule A secretory organelle found in blood platelets, which is unique in that it exhibits further compartmentalization and acquires its protein content via two distinct mechanisms: (1) biosynthesis predominantly at the megakaryocyte (MK) level (with some vestigial platelet synthesis) (e.g. platelet factor 4) and (2) endocytosis and pinocytosis at both the MK and circulating platelet levels (e.g. fibrinogen (Fg) and IgG).
platelet alpha granule membrane The lipid bilayer surrounding the platelet alpha granule.
platelet dense granule Electron-dense granule occurring in blood platelets that stores and secretes adenosine nucleotides and serotonin. They contain a highly condensed core consisting of serotonin, histamine, calcium, magnesium, ATP, ADP, pyrophosphate and membrane lysosomal proteins.
platelet dense granule membrane The lipid bilayer surrounding the platelet dense granule.
pleated septate junction A septate junction in which regular arrays of electron-dense septae span the intermembrane space.
plus-end kinesin complex Any complex that includes a dimer of molecules from the kinesin superfamily and any associated proteins, and moves towards the plus end of a microtubule.
pml body A class of nuclear body; they react against SP100 auto-antibodies (PML, promyelocytic leukemia); cells typically contain 10-30 PML bodies per nucleus; alterations in the localization of PML bodies occurs after viral infection.
podosome An actin-rich adhesion structure characterized by formation upon cell substrate contact and localization at the substrate-attached part of the cell, contain an F-actin-rich core surrounded by a ring structure containing proteins such as vinculin and talin, and have a diameter of 0.5 mm.
polar microtubule Any of the spindle microtubules that come from each pole and overlap at the spindle midzone. This interdigitating structure consisting of antiparallel microtubules is responsible for pushing the poles of the spindle apart.
polar nucleus Either of two nuclei located centrally in a flowering plant embryo sac that eventually fuse to form the endosperm nucleus.
polar tube A highly specialized structure unique to microsporidia that is required for host cell invasion. In the spore, the polar tube is connected at the anterior end, and then coils around the sporoplasm. Upon appropriate environmental stimulation, the polar tube rapidly discharges out of the spore, pierces a cell membrane and serves as a conduit for sporoplasm passage into the new host cell.
polarisome Protein complex that plays a role in determining cell polarity by directing the localized assembly of actin filaments at polarization sites; in Saccharomyces the polarisome includes Bni1p, Spa2p, Pea2p, and Bud6p.
pole plasm Differentiated cytoplasm associated with a pole (animal, vegetal, anterior, or posterior) of an oocyte, egg or early embryo.
polkadots A punctate, filamentous structure composed of Bcl10 that appears in the cytoplasm of T-cells shortly after T-cell receptor stimulation. Polkadots stands for Punctate Oligomeric Killing and Activating DOmains Transducing Signals.
pollen coat A layer of extracellular matrix deposited onto the surface of the pollen wall upon disintegration of the tapetal layer of the anther wall in the late stages of pollen development. The composition of this material is highly heterogeneous and includes waxes, lipid droplets, small aromatic molecules, and proteins. The pollen coat is proposed to have many functions, such as holding pollen in the anther until dispersal, facilitation of pollen dispersal, protection of pollen from water loss and UV radiation, and facilitation of adhesion of pollen to the stigma.
pollen tube A tubular cell projection that is part of a pollen tube cell and extends from a pollen grain.
pollen tube tip The region at growing end of the pollen tube cell, where polarized growth occurs.
pollen wall The complex wall surrounding a pollen grain.
polycystin complex A stable heterodimeric complex composed of polycystin-1 and polycystin-2.
polyhedral organelle An organelle found in bacteria consisting of a proteinaceous coat containing metabolic enzymes whose purpose is the sequestration or concentration of metabolites and which has the appearance of a polygonal granule by electron microscopy.
polyketide synthase complex A protein complex that carries out enzymatic reactions involved in the biosynthesis of polyketides, any of a diverse group of natural products synthesized via linear poly-beta-ketones.
polymeric iga immunoglobulin complex A protein complex composed of two, three, or four monomeric IgA immunoglobulin complexes linked through both direct disulfide bonds and through disulfide binded monomers of J chain acting as a bridge. Each IgA monomer consists of two identical immunoglobulin heavy chains of an IgA isotype and two identical immunoglobulin light chains, held together by disulfide bonds. Dimeric IgA is sometimes complexed additionally with secretory component, and present in the extracellular space, in mucosal areas or other tissues, or circulating in the blood or lymph.
polysomal ribosome A ribosome bound to mRNA that forms part of a polysome.
polysome A multiribosomal structure representing a linear array of ribosomes held together by messenger RNA. They represent the active complexes in cellular protein synthesis and are able to incorporate amino acids into polypeptides both in vivo and in vitro.
polytene chromosome A type of chromosome in a polyploid cell, formed when multiple copies of homologous chromosomes are aligned side by side to give a giant chromosome in which distinct chromosome bands are readily visible.
polytene chromosome band A stretch of densely packed chromatin along the polytene chromosome, visible as a morphologically distinct band.
polytene chromosome chromocenter A region at which the centric regions of polytene chromosomes are joined together.
polytene chromosome interband A stretch of less tightly packed chromatin along the polytene chromosome, found between bands.
polytene chromosome puff A swelling at a site along the length of a polytene chromosome, thought to be the site of active transcription.
pore complex Any small opening in a membrane that allows the passage of gases and/or liquids.
porosome A permanent cup-shaped structure at the cell plasma membrane in secretory cells. Following a secretory stimulus, secretory vesicles transiently dock and fuse at the base of porosomes and release intravesicular contents dictated by the turgor pressure generated from the swelling of secretory vesicles.
porous cell septum A septum or cross wall which does not entirely span the space between two portions of cell wall and may contain a specialized central pore structure. A porous septum allows the movement of organelles and/or cytoplasm between compartments.
positive transcription elongation factor complex b A transcription elongation factor complex that facilitates the transition from abortive to productive elongation by phosphorylating the CTD domain of the large subunit of DNA-directed RNA polymerase II, holoenzyme. Contains cyclin T and a cyclin-dependent protein kinase catalytic subunit.
post-lysosomal vacuole A membrane-bounded intracellular vesicle formed late in the endocytic pathway when the pH in the vacuole becomes neutral prior to exocytosis.
post-spliceosomal complex A spliceosomal complex that is formed following the second splicing event and contains the spliced product, the excised intron, and three snRNPs, including U5.
postsynaptic density The postsynaptic density is a region that lies adjacent to the cytoplasmic face of the postsynaptic membrane at excitatory synapse. It forms a disc that consists of a range of proteins with different functions, some of which contact the cytoplasmic domains of ion channels in the postsynaptic membrane. The proteins making up the disc include receptors, and structural proteins linked to the actin cytoskeleton. They also include signalling machinery, such as protein kinases and phosphatases. The postsynaptic density may be part of a neuron or a muscle cell or a glial cell.
postsynaptic membrane A specialized area of membrane facing the presynaptic membrane on the tip of the nerve ending and separated from it by a minute cleft (the synaptic cleft). Neurotransmitters across the synaptic cleft and transmit the signal to the postsynaptic membrane.
potassium channel complex An ion channel complex through which potassium ions pass.
potassium ion-transporting atpase complex Protein complex that carries out the reaction: ATP + H2O + K+(out) = ADP + phosphate + K+(in). It is a high affinity potassium uptake system. The E. coli complex consists of 4 proteins: KdpA is the potassium ion translocase, KdpB is the ATPase, and KdpC and KdpF seem to be involved in assembly and stabilization of the complex.
pr-dub complex A multimeric protein complex that removes monoubiquitin from histone H2A. In Drosophila and mammals, the core of the complex is composed of Calypso/BAP1 and Asx/ASXL1, respectively.
prc1 complex A multiprotein complex that mediates monoubiquitination of lysine residues of histone H2A (lysine-118 in Drosophila or lysine-119 in mammals). The complex is required for stable long-term maintenance of transcriptionally repressed states and is involved in chromatin remodeling.
pre-autophagosomal structure A punctate structure localized in the vicinity of the vacuole that is required for the formation of autophagosomes.
pre-autophagosomal structure membrane A cellular membrane associated with the pre-autophagosomal structure.
pre-b cell receptor complex An immunoglobulin-like complex that is present in at least the plasma membrane of pre-B cells, and that is composed of two identical immunoglobulin heavy chains and two surrogate light chains, each composed of the lambda-5 and VpreB proteins, and a signaling subunit, a heterodimer of the Ig-alpha and Ig-beta proteins.
pre-replicative complex A protein-DNA complex that forms at the origin of replication during the initial step of DNA replication and allows the origin to become competent, or 'licensed', for replication.
pre-snornp complex A ribonucleoprotein complex that contains a precursor small nucleolar RNA (pre-snoRNA) and associated proteins, and forms during small nucleolar ribonucleoprotein complex (snoRNP) assembly. Pre-snoRNP complexes may contain proteins not found in the corresponding mature snoRNP complexes.
pre-t cell receptor complex A receptor complex found on immature T cells consisting of a T cell receptor beta chain and the pre-TCR-alpha chain, along with additional signaling components including CD3 family members and additional signaling proteins.
precatalytic spliceosome A spliceosomal complex that is formed by the recruitment of a preassembled U5-containing tri-snRNP to the prespliceosome. Although all 5 snRNPs are present, the precatalytic spliceosome is catalytically inactive. The precatalytic spliceosome includes many proteins in addition to those found in the associated snRNPs.
prefoldin complex A multisubunit chaperone that is capable of delivering unfolded proteins to cytosolic chaperonin, which it acts as a cofactor for. In humans, the complex is a heterohexamer of two PFD-alpha and four PFD-beta type subunits. In Saccharomyces cerevisiae, it also acts in the nucleus to regulate the rate of elongation by RNA polymerase II via a direct effect on histone dynamics.
preprophase band A dense band of microtubules, 1-3 pm wide, that appears just beneath the cell membrane before the start of cell division in the cells of higher plants. It precedes the onset of prophase and then disappears as mitosis begins, yet it somehow determines the plane of orientation of the new cell plate forming in late telophase and marks the zone of the parental cell wall where fusion with the growing cell plate ultimately occurs.
preribosome Any complex of pre-rRNAs, ribosomal proteins, and associated proteins formed during ribosome biogenesis.
preribosome, small subunit precursor A preribosomal complex consisting of 20S pre-rRNA, ribosomal proteins including late-associating small subunit proteins, and associated proteins; a precursor of the eukaryotic cytoplasmic small ribosomal subunit.
presequence translocase-associated import motor Protein complex located on the matrix side of the mitochondrial inner membrane and associated with the presequence translocase complex; hydrolyzes ATP to provide the force to drive import of proteins into the mitochondrial matrix.
prespliceosome A spliceosomal complex that is formed by association of the 5' splice site and the branch point sequence with specific snRNPs. The prespliceosome includes many proteins in addition to those found in the bound snRNPs. Commitment to a given pair of 5' and 3' splice sites occurs at the time of prespliceosome formation. Prespliceosome complexes are not active for splicing, but are instead an early step in the assembly of a spliceosomal complex.
presynaptic active zone A specialized region of the plasma membrane and cell cortex of a presynaptic neuron; encompasses a region of the plasma membrane where synaptic vesicles dock and fuse, synaptic vesicles, and a specialized cortical cytoskeletal matrix.
presynaptic active zone membrane The membrane portion of the presynaptic active zone; it is the site where docking and fusion of synaptic vesicles occurs for the release of neurotransmitters.
presynaptic cytoskeletal matrix assembled at active zones The specialized cytoskeletal matrix assembled at the active zones of the presynaptic nerve terminal. The cytoskeletal matrix is a proteinaceous structure involved in organizing synaptic events such as immobilisation or translocation of synaptic vesicles, and assembling active zone components. The cytomatrix protein exclusively assembled at active zones, is thought to form a molecular scaffold that organizes neurotransmitter release sites.
presynaptic grid A hexagonal array of electron dense particles attached to the cytoplasmic face of the presynaptic membrane.
presynaptic membrane A specialized area of membrane of the axon terminal that faces the plasma membrane of the neuron or muscle fiber with which the axon terminal establishes a synaptic junction; many synaptic junctions exhibit structural presynaptic characteristics, such as conical, electron-dense internal protrusions, that distinguish it from the remainder of the axon plasma membrane.
presynaptic periactive zone A region that surrounds the active zone of the presynaptic plasma membrane, and is specialized for the control of synaptic development.
primary cell wall A plant cell wall that is still able to expand, permitting cell growth. Primary cell walls contain more pectin than secondary walls and no lignin is present.
primary cilium A cilium found on many different cell types that is typically present in a single copy per cell. A primary cilium may have a variable array of axonemal microtubules and may or may not contain molecular motors.
primary endosperm nucleus Nucleus resulting from the fusion of the male gamete and two polar nuclei in the central cell of the embryo sac.
primary lysosome A lysosome before it has fused with a vesicle or vacuole.
pronucleus The nucleus of either the ovum or the spermatozoon following fertilization. Thus, in the fertilized ovum, there are two pronuclei, one originating from the ovum, the other from the spermatozoon that brought about fertilization; they approach each other, but do not fuse until just before the first cleavage, when each pronucleus loses its membrane to release its contents.
proplastid The precursor of other plastids.
prospore contractile ring A contractile ring, i.e. a cytoskeletal structure composed of actin filaments and myosin, that forms beneath the plasma membrane of the prospore envelope in meiotic cells in preparation for completing cytokinesis.
prospore membrane The prospore membrane is a double-membraned structure that extends from the cytoplasmic face of the spindle pole bodies to encompass the spindle pole bodies and the four nuclear lobes that are formed during meiosis. It helps isolate the meiotic nuclei from the cytoplasm during spore formation and serves as a foundation for the formation of the spore walls. An example of this component is found in Schizosaccharomyces pombe.
protease inhibitor complex A heterodimeric protein complex that contains a protease inhibitor and a protease; formation of the complex inhibits protease activity.
proteasome accessory complex A protein complex, that caps one or both ends of the proteasome core complex and regulates entry into, or exit from, the proteasome core complex.
proteasome activator complex A multisubunit complex that activates the hydrolysis of small nonubiquitinated peptides by binding to the proteasome core complex.
proteasome complex A large multisubunit complex which catalyzes protein degradation, found in eukaryotes, archaea and some bacteria. In eukaryotes, this complex consists of the barrel shaped proteasome core complex and one or two associated proteins or complexes that act in regulating entry into or exit from the core.
proteasome core complex A multisubunit barrel shaped endoprotease complex, which is the core of the proteasome complex.
proteasome regulatory particle A multisubunit complex, which caps one or both ends of the proteasome core complex. This complex recognizes and unfolds ubiquitinated proteins, and translocates them to the proteasome core complex.
proteasome storage granule A multisubunit proteasome complex that localizes in the cytoplasm as dot-like structures when cells are in a quiescent state.
proteasome-activating nucleotidase complex A homohexameric complex that recognizes and unfolds core proteasome substrate proteins, and translocates them to the core complex in an ATP dependent manner.
protein acetyltransferase complex A complex that catalyzes the transfer of an acetyl group to a protein acceptor molecule.
protein body A membrane-bounded plant organelle found in the developing endosperm, contains storage proteins.
protein c inhibitor-thrombin complex A heterodimeric protein complex that contains protein C inhibitor (SERPINA5) and thrombin (F2); formation of the complex inhibits the serine protease activity of thrombin.
protein complex Any macromolecular complex composed (only) of two or more polypeptide subunits along with any covalently attached molecules (such as lipid anchors or oligosaccharide) or non-protein prosthetic groups (such as nucleotides or metal ions). Prosthetic group in this context refers to a tightly bound cofactor. The component polypeptide subunits may be identical.
protein complex involved in cell adhesion Any protein complex that is capable of carrying out some part of the process of cell-cell adhesion.
protein complex involved in cell-matrix adhesion Any protein complex that is capable of carrying out some part of the process of cell-matrix adhesion.
protein kinase ck2 complex A protein complex that possesses protein serine/threonine kinase activity, and contains two catalytic alpha subunits and two regulatory beta subunits. Protein kinase CK2 complexes are found in nearly every subcellular compartment, and can phosphorylate many protein substrates in addition to casein.
protein kinase complex A protein complex which is capable of protein kinase activity.
protein n-acetylglucosaminyltransferase complex Heterotrimeric enzyme complex, which in humans is composed of two large subunits of the same size, and one smaller subunit. Functions in the addition of nucleotide-activated sugars onto the polypeptide.
protein phosphatase 4 complex The complex formed by the catalytic subunit of protein phosphatase 4 plus a regulatory subunit.
protein serine/threonine phosphatase complex A complex, normally consisting of a catalytic and a regulatory subunit, which catalyzes the removal of a phosphate group from a serine or threonine residue of a protein.
protein storage vacuole A storage vacuole that contains a lytic vacuole; identified in plants.
protein storage vacuole membrane The lipid bilayer surrounding a protein storage vacuole.
protein-carbohydrate complex A macromolecular complex containing separate protein and carbohydrate molecules. Separate in this context means not covalently bound to each other.
protein-dna complex A macromolecular complex containing both protein and DNA molecules.
protein-dna-rna complex A macromolecular complex containing protein, DNA, and RNA molecules.
protein-lipid complex A macromolecular complex containing separate protein and lipid molecules. Separate in this context means not covalently bound to each other.
proteinaceous extracellular matrix A layer consisting mainly of proteins (especially collagen) and glycosaminoglycans (mostly as proteoglycans) that forms a sheet underlying or overlying cells such as endothelial and epithelial cells. The proteins are secreted by cells in the vicinity. An example of this component is found in Mus musculus.
proteinoplast A leucoplast in which protein is stored.
prothylakoid Underdeveloped thylakoids found in etioplasts, lacking competent photosynthetic membranes. Rapidly develop into mature thylakoids in the presence of light.
prothylakoid membrane The membrane of prothylakoids, underdeveloped thylakoids found in etioplasts, lacking competent photosynthetic membranes.
proton-transporting atp synthase complex A proton-transporting two-sector ATPase complex that catalyzes the phosphorylation of ADP to ATP during oxidative phosphorylation. The complex comprises a membrane sector (F0) that carries out proton transport and a cytoplasmic compartment sector (F1) that catalyzes ATP synthesis by a rotational mechanism; the extramembrane sector (containing 3 a and 3 b subunits) is connected via the d-subunit to the membrane sector by several smaller subunits. Within this complex, the g and e subunits and the 9-12 c subunits rotate by consecutive 120 degree angles and perform parts of ATP synthesis. This movement is driven by the hydrogen ion electrochemical potential gradient.
proton-transporting atp synthase complex, catalytic core f(1) The sector of a hydrogen-transporting ATP synthase complex in which the catalytic activity resides; it comprises the catalytic core and central stalk, and is peripherally associated with a membrane, such as the plasma membrane or the mitochondrial inner membrane, when the entire ATP synthase is assembled.
proton-transporting atp synthase complex, coupling factor f(o) All non-F1 subunits of a hydrogen-transporting ATP synthase, including integral and peripheral membrane proteins.
proton-transporting two-sector atpase complex A large protein complex that catalyzes the synthesis or hydrolysis of ATP by a rotational mechanism, coupled to the transport of protons across a membrane. The complex comprises a membrane sector (F0, V0, or A0) that carries out proton transport and a cytoplasmic compartment sector (F1, V1, or A1) that catalyzes ATP synthesis or hydrolysis. Two major types have been characterized: V-type ATPases couple ATP hydrolysis to the transport of protons across a concentration gradient, whereas F-type ATPases, also known as ATP synthases, normally run in the reverse direction to utilize energy from a proton concentration or electrochemical gradient to synthesize ATP. A third type, A-type ATPases have been found in archaea, and are closely related to eukaryotic V-type ATPases but are reversible.
proton-transporting two-sector atpase complex, catalytic domain A protein complex that forms part of a proton-transporting two-sector ATPase complex and catalyzes ATP hydrolysis or synthesis. The catalytic domain (F1, V1, or A1) comprises a hexameric catalytic core and a central stalk, and is peripherally associated with the membrane when the two-sector ATPase is assembled.
proton-transporting two-sector atpase complex, proton-transporting domain A protein complex that forms part of a proton-transporting two-sector ATPase complex and carries out proton transport across a membrane. The proton-transporting domain (F0, V0, or A0) includes integral and peripheral membrane proteins.
provirus The name given to a viral genome after it has been integrated into the host genome; particularly applies to retroviruses and is a required part of the retroviral replication cycle.
prp19 complex A protein complex consisting of Prp19 and associated proteins that is involved in the transition from the precatalytic spliceosome to the activated form that catalyzes step 1 of splicing, and which remains associated with the spliceosome through the second catalytic step. It is widely conserved, found in both yeast and mammals, though the exact composition varies. In S. cerevisiae, it contains Prp19p, Ntc20p, Snt309p, Isy1p, Syf2p, Cwc2p, Prp46p, Clf1p, Cef1p, and Syf1p.
pseudopodium A temporary protrusion or retractile process of a cell, associated with flowing movements of the protoplasm, and serving for locomotion and feeding.
pseudopodium membrane The portion of the plasma membrane surrounding a pseudopodium.
psi associated light-harvesting complex i Protein-pigment complex associated with photosystem I.
psii associated light-harvesting complex ii Protein-pigment complex associated with photosystem II.
pterinosome A tissue-specific, membrane-bounded cytoplasmic organelle within which pteridine pigments are synthesized and stored. Pterinosomes are synthesized in xanthophores and erythrophore cells and are yellow, orange or red in appearance.
ptw/pp1 phosphatase complex A protein serine/threonine phosphatase complex that contains a catalytic subunit (PPP1CA, PPP1CB or PPP1CC) and the regulatory subunits PPP1R10 (PNUTS), TOX4 and WDR82, and plays a role in the control of chromatin structure and cell cycle progression during the transition from mitosis into interphase.
puncta adhaerentia A small version of the zonula adherens type junction, characterized by a symmetrical adherent point between two cells.
pwp2p-containing subcomplex of 90s preribosome A protein complex that forms a subcomplex of the 90S preribosome and can interact directly with the 5' External Transcribed Spacer (ETS) of the full length pre-rRNA transcript. In S. cerevisiae, it sediments at 25-30 S and is composed of Pwp2p, Dip2p, Utp21p, Utp13p, Utp18p, and Utp6p.
pyrophosphate-dependent phosphofructokinase complex Heterodimeric complex that catalyzes the pyrophosphate-dependent phosphorylation of D-fructose 6-phosphate into D-fructose 1,6-bisphosphate.
pyruvate dehydrogenase complex Complex that carries out the oxidative decarboxylation of pyruvate to form acetyl-CoA; comprises subunits possessing three catalytic activities: pyruvate dehydrogenase (E1), dihydrolipoamide S-acetyltransferase (E2), and dihydrolipoamide dehydrogenase (E3).
r2tp complex A highly conserved protein complex comprised of two ATP-dependent DNA helicases (Rvb1p and Rvb2p in yeast, Pontin52 and Reptin52 in humans), Pih1p in yeast or PIH1D1 in humans, and Tah1 in yeast or RPAP3 in humans. The complex associates with Hsp90 and is thought to have a role in assembly of large protein or protein/nucleic acid complexes. In this role it is involved in multiple processes such as box C/D snoRNP biogenesis, phosphatidylinositol-3 kinase-related protein kinase (PIKK) signaling, RNA polymerase II assembly, and others.
rab-protein geranylgeranyltransferase complex A heterodimeric enzyme complex, which in mammals is composed of an alpha and a beta subunit, and which associates with an accessory protein Rep (Rab escort protein). Catalyzes of the transfer of a geranyl-geranyl group from geranylgeranyl pyrophosphate to a Rab protein.
rad17 rfc-like complex A pentameric protein complex related to replication factor C, which loads a trimeric complex of checkpoint proteins (known as the checkpoint clamp or 9-1-1 complex) onto DNA at damage sites; functions in DNA damage cell cycle checkpoints. In Schizosaccharomyces pombe the subunits are known as Rad17, Rfc2, Rfc3, Rfc4, and Rfc5, while in Saccharomyces cerevisiae the subunits are known as Rad24p, Rfc2p, Rfc3p, Rfc4p, and Rfc5p.
rad51b-rad51c complex A DNA recombinase mediator complex that contains the Rad51 paralogs RAD51B and RAD51C, or orthologs thereof.
rad51b-rad51c-rad51d-xrcc2 complex A DNA recombinase mediator complex that contains the Rad51 paralogs RAD51B, RAD51C, RAD51D, and XRCC2, or orthologs thereof.
rad51c-xrcc3 complex A DNA recombinase mediator complex that contains the Rad51 paralogs RAD51C and XRCC3, or orthologs thereof.
radial spoke Protein complex that links the outer microtubule doublet of the ciliary or flagellum axoneme with the sheath that surrounds the central pair of microtubules. Composed of a stalk that attaches to each doublet microtubule and a globular structure (spoke head) that projects toward the central pair of microtubules.
radial spoke stalk Globular portion of the radial spoke that projects towards the central pair of microtubules.
radial spokehead Protein complex forming part of eukaryotic flagellar apparatus.
ragulator complex A protein complex that contains MAPKSP1 (MP1, Map2k1ip1), ROBLD3 (p14, Mapbpip), and C11orf59 (p18). The complex is anchored to lipid rafts in late endosome membranes via C11orf59, recruits mTORC1 to lysosomal membranes in amino acid signaling to mTORC1, and is also involved in ERK/MAPK signaling.
rave complex A multisubunit complex that in Saccharomyces is composed of three subunits, Rav1p, Rav2p and Skp1p. Acts transiently to catalyze assembly of cytoplasmic V1, with membrane embedded V0 to form the V-ATPase holoenzyme.
rcaf complex A protein complex that facilitates the assembly of nucleosomes on to newly synthesized DNA. In Drosophila, the complex comprises ASF1 and histones H3 and H4.
receptor complex Any protein complex that undergoes combination with a hormone, neurotransmitter, drug or intracellular messenger to initiate a change in cell function.
recfor complex A heterotrimeric complex composed of the subunits RecF, RecO and RecR. Mediates the loading of RecA protein specifically onto SSB-coated gapped DNA during DNA repair.
recombination nodule An electron dense structure that is associated with meiotic chromosomes.
recq helicase-topo iii complex A complex containing a RecQ family helicase and a topoisomerase III homologue; may also include one or more additional proteins; conserved from E. coli to human.
recurrent axon collateral Axon collateral that ramifies in the area of the soma of the cell of origin.
recycling endosome Organelle consisting of networks of 60nm tubules organized around the microtubule organizing centre in some cell types. They transport molecules (e.g., receptors, transporters, lipids) derived from endosomes, the Golgi apparatus, or the cytoplasm to the plasma membrane. Transported molecules may be recycled for reuse, or may be newly synthesized.
recycling endosome membrane The lipid bilayer surrounding a recycling endosome.
rent complex A protein complex that mediates transcriptional silencing at the rDNA locus (the name derives from regulator of nucleolar silencing and telophase). In Saccharomyces the complex contains Net1p, Sir2p, Cdc14p, and at least one more subunit.
replication compartment Globular nuclear domains where the transcription and replication of the viral genome occurs. More than one site can be present simultaneously.
replication fork The Y-shaped region of a replicating DNA molecule, resulting from the separation of the DNA strands and in which the synthesis of new strands takes place. Also includes associated protein complexes.
replication fork protection complex A protein complex conserved in eukaryotes and associated with the replication fork; the complex stabilizes stalled replication forks and is thought to be involved in coordinating leading- and lagging-strand synthesis and in replication checkpoint signaling.
replisome A multi-component enzymatic machine at the replication fork which mediates DNA replication. Includes DNA primase, one or more DNA polymerases, DNA helicases, and other proteins.
res complex A protein complex that is required for efficient splicing, and prevents leakage of unspliced pre-mRNAs from the nucleus (named for pre-mRNA REtention and Splicing). In Saccharomyces, the complex consists of Ist3p, Bud13p, and Pml1p.
respiratory chain The protein complexes that form the electron transport system (the respiratory chain), associated with a cell membrane, usually the plasma membrane (in prokaryotes) or the inner mitochondrial membrane (on eukaryotes). The respiratory chain complexes transfer electrons from an electron donor to an electron acceptor and are associated with a proton pump to create a transmembrane electrochemical gradient.
respiratory chain complex i Respiratory chain complex I is an enzyme of the respiratory chain. It consists of several polypeptide chains and is L-shaped, with a horizontal arm lying in the membrane and a vertical arm that projects into the matrix. The electrons of NADH enter the chain at this complex.
respiratory chain complex ii A part of the respiratory chain, containing the four polypeptide subunits of succinate dehydrogenase, flavin-adenine dinucleotide and iron-sulfur. Catalyzes the oxidation of succinate by ubiquinone. Connects the TCA cycle with the respiratory chain.
respiratory chain complex iii A protein complex that transfers electrons from ubiquinol to cytochrome c and translocates two protons across a membrane. The complex contains a core structure of three catalytic subunits: cytochrome b, the Rieske iron sulfur protein (ISP), and cytochrome c1, which are arranged in an integral membrane-bound dimeric complex; additional subunits are present, and vary among different species.
respiratory chain complex iv A part of the respiratory chain, containing the 13 polypeptide subunits of cytochrome c oxidase, including cytochrome a and cytochrome a3. Catalyzes the oxidation of reduced cytochrome c by dioxygen (O2).
retromer complex A conserved multimeric membrane-associated complex involved in retrograde transport from endosomes to the Golgi apparatus. For example, the budding yeast retromer comprises Vps35p, Vps29p, Vps26p, Vps5p, and Vps17p.