Pak2 (p21-activated protein kinase 2) is the serine/threonine protein kinase PAK I, which was first detected as a protease activated form in Dr. Traugh’s laboratory in early 1980s (Tahara and Traugh 1981, 1982). Pak2 was further cloned and sequenced in the same lab in 1996 (Jakobi et al. 1996). Pak2 belongs to the PAK (p21-activated protein kinase) family, which can be activated by Rac and Cdc42 (Manser et al. 1994). The PAK family consists of group I protein kinases, including the highly homologous Pak1 (α-PAK), Pak2 (γ-PAK), and Pak3 (β-PAK), and the recently identified group II, including Pak4, Pak5, and Pak6 (Jaffer and Chernoff 2002). The 60-kDa Pak1 is expressed in brain and is also detected in muscle and spleen. The 60-kDa Pak3 is expressed mainly in brain. Pak2 is 58 kDa and expressed ubiquitously in mammalian cells (Roig and Traugh 2001) (http://www.genecards.org/cgi-bin/carddisp.pl?gene=PAK2).