Amino acid 61 is a determinant of sensitivity of rap proteins to the ras GTPase activating protein.

The GTPase activating protein (ras-GAP) has been shown to interact with p21ras at a domain defined by amino acids 32-40. The sequences of the rap family of ras related proteins (including a suppressor of ras transformation Krev-1/rap1A) are identical to ras in this region. Incubation of rap1A protein with ras-GAP does not accelerate the rate of GTP hydrolysis by p21rap1A. Rap proteins have threonine at amino acid 61, whereas ras proteins have glutamine at this site and mutation to threonine reduces the intrinsic GTPase of p21ras. We have, therefore, mutated thr61 of p21rap1A to glutamine and shown that ras-GAP is now able to accelerate the rate of hydrolysis of GTP. This demonstrates that ras-GAP can interact with rap and that the sensitivity to ras-GAP is determined in part by the amino acid at codon 61.