Small GTPases are a super-family of cellular signaling regulators. Rac belongs to the Rho sub-family of GTPases that regulate cell motility, cell division, and gene transcription. In mammals, there are three Rac genes: Rac1, Rac2 and Rac3. GTP binding increases the activity of Rac, and the hydrolysis of GTP to GDP renders it inactive. GTP hydrolysis is aided by GTPase activating proteins (GAPs), while exchange of GDP for GTP is facilitated by guanine nucleotide exchange factors (GEFs). 

Western blot analysis of Rac1 proteins. MEF whole-cell lysate was used for western blots. The monoclonal anti Rac1 antibody was pre-incubated without (lane 1) or with (lane 2) the antigen protein (Rac1) to show the specificity.