Function of the post-translationally modified C-terminal region of rho p21

rhoA p21, a ras p21-like small GTP-binding protein, purified from bovine aortic smooth muscle is similarly modified at its C-terminal region as described for ras p21s. In this study, I examined the role of the post-translational modifications of the C-terminal region of rhoA p21 by comparing bovine rhoA p21 with bacterially-produced rhoA p21 because the bacterial protein was not modified. Bovine rhoA p21 bound to plasma membranes, but bacterial rhoA p21 did not. Both the stimulatory and inhibitory GDP/GTP exchange proteins for bovine rhoA p21 were inactive for bacterial rhoA p21. On the other hand, the GTPase activating protein for bovine rhoA p21 was also active for bacterial rhoA p21. These results indicate that the post-translational modifications of the C-terminal region of bovine rhoA p21, which are absent in bacterial rhoA p21, are essential for its interaction with membranes and the stimulatory and inhibitory GDP/GTP exchange proteins but not with the GTPase activating protein.