ENU mutagenesis induced an A to T nucleotide exchange that alters amino acid leucine 1396 to glutamine in the C-terminal RhoGAP domain. The L1396Q substitution is a loss-of-function mutation that results in decreased GTPase-activating protein (GAP) activity for the prototypical Rho family members, RhoA and Rac1, likely due to disrupted ordering of the Rho binding surface.