FIG. 9.
Mutation of Ser608 interferes with lipid kinase activity and heterodimer formation. Each of the Ser608 mutants of Myc-tagged p85α was coexpressed together with Flag-tagged p110α in HEK 293 cells, and the heterodimers were isolated by immunoprecipitation with antibody 9E10. Immunoprecipitates were split in two. One half of each immunoprecipitate was assayed for lipid kinase activity by using phosphatidylinositol and [γ-32P]ATP as the substrates. Reaction products were analyzed by thin-layer chromatography and autoradiography (autorad). The other half was assayed by immunoblotting with antibody 9E10, followed by stripping of the blot and reprobing with an anti-Flag antibody. (A) A representative experiment. IB, immunoblot. (B) Data from three experiments were plotted in a graph. Values are means ± standard errors of the means; *, P < 0.05 for the mutant versus the wild type.