CHARACTERIZATION OF PAK2P, A PLECKSTRIN HOMOLOGY DOMAIN-CONTAINING, P21-ACTIVATED PROTEIN-KINASE FROM FISSION YEAST

p21-activated kinases (PAKs) bind to and are activated by Rho family G TPases such as Cdc42 and Rac. Since these GTPases play key roles in re gulating cell polarity, stress responses, and cell cycle progression, the ability of PAK to affect these processes has been examined, me pre viously showed that fission yeast pak1(+) encodes an essential protein that affects mating and cell polarity. Here, we characterize a second pak gene (pak2(+)) from Schizosaccharomyces pombe. Like the Saccharom yces cerevisiae proteins Cla4p and Skm1p, fission yeast Pak2p contains an N-terminal pleckstrin homology domain in addition to a pal-binding domain and a protein kinase domain that are common to other members o f the PAK family. Unlike pak1(+), pak2+ is not essential for vegetativ e growth or for mating in S. pombe. Overexpression of the wild-type pa k2(+) allele suppresses the lethal growth defect associated with delet ion of pak1(+), and this suppression requires both the pleckstrin homo logy- and the pll-binding domains of Pak2p, as well as kinase activity . A substantial fraction of Pak2p is associated with membranous compon ents, an association mediated both by the pleckstrin homology- and by the pal-binding domains. These results show that S. pombe encodes at l east two pak genes with distinct functions and suggest that the membra ne localization of Pak2p, directed by its interactions with membrane l ipids and Cdc42p, is critical to its biological activity.