ARHGAP1(also p50-RhoGAP and CDC42 GTPase-activating protein) is a 50kD member of the ARHGAP family of proteins. It is preferentially expressed in epithelium, and serves as a cytoplasmic protein that deactivates Rho-family GTPases. It does so by contributing an Arg residue (Arg282)to Cdc42 and RhoA, which activates their intrinsic GTPase activity and converts GTP-associated molecules into inactivating GDP molecules. Human ARHGAP1 is 439aa in length and contains one CRAL-TRIO domain that binds small lipophilic molecules (aa53-218), an SH3 binding site (aa228-238) and one C-terminal RhoGAP domain (aa244-431). There are phosphorylation sites at Ser51 and Tyr65. There is one potential splice form with a 24aa substitution for (aa1-150)coupled to a 26aa substitution for (aa300-439), Over (aa1-62, human ARHGAP1 shares 96% aa identity with mouse ARHGAP1.