NCBI - COGS
attempt to reconstruct the phylogenetic relationships between organisms by comparing the protein sequences encoded in 43 complete genomes, representing 30 major phylogenetic lineages,
a COG consists of individual proteins or groups of paralogs from at least 3 lineages and thus corresponds to an ancient conserved domain.
COGs applied to D.melanogaster and C.elegans
search for COGs by sequence, functional group, phylogenetic relationship or pathway