Serine/threonine-protein kinase PAK-1 (PAK-1) is a protein kinase that acts on a variety of targets. PAK-1 is the GTPase effector that links the Rho-related GTPases to the JNK MAP kinase pathway. PAK-1 is activated by CDC42 and RAC1, and is involved in dissolution of stress fibers and reorganization of focal complexes. PAK-1 is involved in regulation of microtubule biogenesis through phosphorylation of TBCB. PAK-1 activity is inhibited in cells undergoing apoptosis, potentially due to binding of CDC2L1 and CDC2L2.