Cloning of the GST-PAK-CD fusion protein (encompassing amino acids 56–141 from PAK1B), containing the Rac and Cdc42 binding region from human PAK1B, has been described (Sander et al. 1998). GST-C21 has been described by Reid et al. 1996, Reid et al. 1999 and contains the NH2-terminal 90 amino acids, representing the Rho binding domain, from the Rho effector protein Rhotekin. Escherichia coli BL21 cells transformed with the GST-PAK-CD construct were grown at 37°C, cells transformed with the GST-C21 construct were grown at 30°C to OD600 0.3. Expression and purification of recombinant proteins has been described (Sander et al. 1998).