Protein Complexes

Definition of a Protein Complex

A cellular component should include more than one gene product; complexes of one gene product with a cofactor, e.g. heme and chlorophyll, should not be included. Homomultimeric proteins, e.g. the homodimeric alcohol dehydrogenase, may be included as cellular component terms, as should heteromultimeric proteins, e.g. hemoglobin with alpha and beta chains.

Membrane Proteins

As GO cellular component terms describe locations where a gene product may act, rather than physical features of proteins or RNAs, the terms integral membrane protein and peripheral membrane protein are present only as non-exact synonyms. GO distinguishes classes of membrane-related location:

extrinsic component of membrane ; GO:0019898 refers to gene products that are associated with membranes, but are neither directly embedded in the membrane nor anchored by covalent bonds to any moiety embedded in the membrane.


The set of standard terms below can be applied to each developing structure in each species covered in the ontology. However it is generally not practical to implement every term for every structure, since this would lead to a massive proliferation of terms. Where one term e.g. x development, is present, the rest of the terms for the development of x are considered to be implied, without having actually been implemented. Further terms are generally only implemented when they are required for annotation.

The Cell Cycle

The representation of the cell cycle in GO is split into two sections: the physical processes that occur and the temporal stages—prophase, anaphase and so on—used to describe sets of events. This method of representation is used to prevent true path problems when organisms differ from the "canonical" (usually S. cerevisiae) cell cycle.

Terms and Structure

The cell cycle node sits under cellular process ; GO:0007049 and is split into types of cell cycle (meiotic or mitotic) and stages (M phase, S phase, etc.), plus a regulation term.

  • cell cycle

    Ontology Related Information

    The Gene Ontology project provides an ontology of defined terms representing gene product properties. The ontology covers three domains: cellular component, the parts of a cell or its extracellular environment; molecular function, the elemental activities of a gene product at the molecular level, such as binding or catalysis; and biological process, operations or sets of molecular events with a defined beginning and end, pertinent to the functioning of integrated living units: cells, tissues, organs, and organisms.

    Other Useful Links

    • SourceForge links: Useful links for the SourceForge site, including both general and GO-specific pages.
    • CVS Help: Help page for those who wish to access the anonymous GO CVS repository
    • GO Editor Guides: A set of guides for curators editing the ontologies.

    File Format Guide

    GO Formats

    The GO File Format Guide documents the structure and syntax of the files available on the GO website, to assist users who need to read, write parsers for, or create these files. The following file formats are documented separately: