Members of the Ras superfamily of GTPases are distantly related to the heterotrimeric G proteins and shuttle between inactive and active GTP-bound forms. Interconversion between these forms is controlled by guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). The subfamilies of the Ras-like proteins share 30-50% homology, each member participates in a particular set of cellular functions. The Rho (Ras homolog) proteins (A, B, & C) are highly homologous and contain the consensus amino acid sequences necessary for GDP/GTP-binding and GTPase activity. Rho proteins contain a C-terminal sequence, CAAL, whose post-translational modification regulates Rho activation and function. Rho proteins modulate the in vitro activity of PI-3-kinase, PI- 4,5-kinase, and phospholipase D. Rho is a molecular switch that regulates cell morphology and motility in response to extracellular signals. Due to sequence homology among various small GTPase family members, potential cross-reactivity could be observed with this antibody. Based on recent testing in native ELISA with recombinant proteins to CDC42 and Rac1, we have concluded that this antibody recognizes CDC42 and Rac1. BD Pharmingen has not performed such cross-reactivity testing on other family members.