IDENTIFICATION OF A MOUSE P21(CDC42 RAC) ACTIVATED KINASE/

We have isolated a novel member of the mammalian PAI( (p21 activated k inase) and yeast Ste20 serine/threonine kinase family from a mouse fib roblast cDNA library, designated mPAK-3. Expression of mPAK-3 in Sacch aromyces cerevisiae partially restores mating function in ste20 null c ells. Like other PAKs, mPAK-3 contains a putative Cdc42Hs/Rac binding sequence and when transiently expressed in COS cells, full-length mPAK -3 binds activated (GTP gamma S (guanosine 5'-3-O-(thiotriphosphate)-b ound) glutathione S-transferase (GST)-Cdc42Hs and GST-Rac1 but not GST -RhoA. As expected for a putative target molecule, mPAX-3 does not bin d to an effector domain mutant of Cdc42Hs. Furthermore, activated His- tagged Cdc42Hs and His-tagged Rac stimulate mPAK-3 autophosphorylation and phosphorylation of myelin basic protein by mPAK-3 in vitro. Inter estingly, the amino-terminal region of mPAK-3 contains potential SH3-b inding sites and we find that mPAK-3, expressed in vitro and in vivo, shows highly specific binding to the SH3 domain of phospholipase C-gam ma and at least one SH3 domain in the adapter protein Nck. These resul ts raise the possibility of an additional level of regulation of the P AK family in vivo.