The turkey c-rap1A proto-oncogene is expressed via two distinct promoters

The turkey c-K-ras(B) transcript and two species of the turkey rap1A transcripts transcribed from two distinct promoters were isolated from a turkey spleen cDNA library. Turkey K-Ras and Rap1A proteins shared extensive amino acid (aa) sequence relatedness throughout their major functional domains: the four GTP-binding domains, the effector region and the C-terminal CAAX box. However, they diverged significantly in their intervening regions. In contrast, almost complete identity in the aa composition was exhibited between turkey K-Ras and Rap1A and their human homologues. The complete conservation that exists between turkey and human Rap1A, also along the polybasic C-terminal domain as opposed to Rap1B, suggests the functional relevance of these divergent residues in specifying the distinct biological functions of these two closely related proteins.