FIGURE 1.

PI(4,5)P₂ selectively enhances Cdc42-dependent Pak1 activation. Left, the experimental system. Synthetic liposomes (double black circle) with bound Cdc42-His (rectangles) that either contained phosphoinositide (small dark circles) or not, were incubated with Pak1 and [γ-³²P]ATP to monitor phosphoinositide-dependent Pak1 autophosphorylation. Right, Pak1 autophosphorylation in kinase assays with Cdc42-His-bound liposomes (comprised of equimolar PC:PI and containing 7% (by mole) DGS-NTA(Ni) with or without 6% of the indicated phosphoinositides) is plotted normalized to control reactions with Cdc42-containing liposomes without the test phosphoinositide. Pak1 autophosphorylation was quantified by PhosphorImager analysis of dried electrophoretic gels of the reaction products. Mean results are shown from two independent replicates ± S.D.