GO Annotation The Gene Ontology, or GO, is a major bioinformatics initiative to unify the representation of gene and gene product attributes across all species. More specifically, the project aims to: 1. Maintain and develop its controlled vocabulary of gene and gene product attributes; 2. Annotate genes and gene products, and assimilate and disseminate annotation data; 3. Provide tools for easy access to all aspects of the data provided by the project. The ontology covers three domains: 1. Cellular component: A cellular component is just that, a component of a cell, but with the proviso that it is part of some larger object; this may be an anatomical structure (e.g. rough endoplasmic reticulum or nucleus) or a gene product group (e.g. ribosome, proteasome or a protein dimer). 2. Molecular function: Molecular function describes activities, such as catalytic or binding activities, that occur at the molecular level. GO molecular function terms represent activities rather than the entities (molecules or complexe