Recombinant protein purified from E. coli, consisting of GST fused to the Cdc42 (p21) binding domain (CRIB) of the human p21 activated kinase 1 protein (PAK). This non-radioactive pulldown assay uses the p21 binding domain (PBD) of the Rac/Cdc42, p21-activated protein kinase (PAK1). This domain is expressed as an N-terminal GST-fusion protein coupled to glutathione beads and can be used to isolate the active, GTP-bound form of Rac/Cdc42 from whole cell lysates. After precipitation, Rac/Cdc42 can be detected by immunoblotting with the appropriate antibodies.