THE TURKEY C-RAP1A PROTOONCOGENE IS EXPRESSED VIA 2 DISTINCT PROMOTERS

The turkey c-K-ras(B) transcript and two species of the turkey rap1A t ranscripts transcribed from two distinct promoters were isolated from a turkey spleen cDNA library. Turkey K-Ras and Rap1A proteins shared e xtensive amino acid (aa) sequence relatedness throughout their major f unctional domains: the four GTP-binding domains, the effector region a nd the C-terminal CAAX box. However, they diverged significantly in th eir 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 oppose d to Rap1B, suggests the functional relevance of these divergent resid ues in specifying the distinct biological functions of these two close ly related proteins.