EMERGING FROM THE PAK - THE P21-ACTIVATED PROTEIN-KINASE FAMILY

The p21-activated protein kinases (PAKs) are members of a growing fami ly of regulatory enzymes that may play roles in diverse phenomena such as cellular morphogenesis, the stress response and the pathogenesis o f AIDS. PAKs were initially discovered as binding partners for small ( 21 kDa) GTPases that regulate actin polymerization, and recent evidenc e has shown that some members of the PAK family may be effectors for r elated GTPases that are involved in intracellular vesicle trafficking. Because the downstream signalling pathways for all such GTPases are p oorly understood, intense studies are under way to discern the role of PAK and its cousins. In this review, the authors highlight some of th e established properties of the extended PAK family and discuss curren t controversies regarding their possible roles as GTPase effectors.