Fig. 1. Amino-acid sequence of the human (Hs) Rap1a GTP-binding protein compared to the primary structures of its Drosophila melanogaster (Dm), Dictyostelium discoideum (Dd) and Saccharomyces cerevisiae (Sc/Bud1) homologs and three other human Ras subfamily members: Rap2a, R-Ras and H-Ras. Boxes define regions of identity between all sequences, whereas the overall homology is shown in blue. Notice the total identity between Rap1 homologs and Ras in the main effector-binding region, delineated by the red bar (amino acids 32-42). Also of note is the high degree of conservation in primary sequence amongst the 4 Rap1 homologs, with homology indicated in yellow. Significant homology is defined here as a score of over 85% in the Dayhoff PAM250 scale. For commodity, several stretches of sequence have been deleted from this alignment. These include the two N-terminal residues in Dd Rap1, the first 26 amino acids in R-Ras and two regions unique to Bud1. Arrowheads indicate the position of these latter two deletions, which correspond respectively to amino acids 171-226 (1) and amino acids 236-258 (2).