A GENOMIC PERSPECTIVE ON PROTEIN FAMILIES

In order to extract the maximum amount of information from the rapidly accumulating genome sequences, all conserved genes need to be classif ied according to their homologous relationships. Comparison of protein s encoded in seven complete genomes from five major phylogenetic linea ges and elucidation of consistent patterns of sequence similarities al lowed the delineation of 720 clusters of orthologous groups (COGs). Ea ch COG consists of individual orthologous proteins or orthologous sets of paralogs from at least three lineages. Orthologs typically have th e same function, allowing transfer of functional information from one member to an entire COG. This relation automatically yields a number o f functional predictions for poorly characterized genomes. The COGs co mprise a framework for functional and evolutionary genome analysis.