Figure 1. Regulation of Rho GTPase activity by GEFs, GAPs, and GDIs. At the membrane, inactive, GDP-bound Rho GTPases can be activated by GEFs, which catalyze the exchange of GDP for GTP. Once GTP-bound, Rho GTPases can bind to a variety of downstream effectors and elicit diverse responses. GAPs catalyze the GTPase-dependent hydrolysis of GTP back into GDP, thus inactivating Rho proteins. In the cytosol, Rho GTPases are bound by GDIs which prevent nucleotide exchange and bury the prenylated C-terminus, thus preventing degradation.