Location of the altered amino acid residues of the Pak1open mutants in the highly conserved region of PAK proteins. The highly conserved regions on Pak1 (17, 26), STE20 (28), CLA4 (7), and three major mammalian PAK isoforms (3, 16, 21) are aligned, with identical residues in black boxes, conserved residues in grey boxes, and the residues altered in the Pak1open mutants indicated by arrows.