A novel gene encoding a ras-like GTP-binding protein from Trypanosoma brucei: an evolutionary ancestor of the ras and rap genes of higher eukaryotes?

The ras superfamily of GTP binding proteins encompasses a aide range of fam ily members, related by conserved amino-acid motifs, and act as molecular b inary switches that play key roles in cellular processes. Gene duplication and divergence has been postulated as the mechanism by which such family me mbers have evolved their specific functions. We have cloned and sequenced a ras-like gene, tbrlp, from the primitive eukaryote Trypanosoma brucei. The gene encodes a protein of 227 amino acids and contains the six conserved s ubdomains that designate it as a ras/rap subfamily member. However, the pre sence of key diagnostic residues characteristic of both the ras and rap fam ilies of GTP confuse the familial classification of this gene. Phylogenetic analysis of the GTP binding domain places its origins at the divergence po int of the ras/rap families and suggests that tbrlp is an ancestral gene to the ras/rap genes of higher eukaryotes. (C) 1999 Elsevier Science B.V. All rights reserved.