FIG. 4.

Inhibition of p110α by dephosphorylated p85. (A) Forty-eight hours after infection with p85 baculovirus, Sf-9 cells were labeled with [³²P]orthophosphate for 4 h. The cells were lysed, treated with recombinant protein phosphatase 1 (0.5 μg) or not treated, and immunoprecipitated with anti-p85–protein A–Sepharose beads. Proteins were eluted and separated by SDS-PAGE, and the dried gel was visualized by autoradiography and quantitated with a Molecular Dynamics PhosphorImager. (B) Lysates from Sf-9 cells expressing p85 were treated in the absence or presence of recombinant protein phosphatase 1 (0.5 μg). p85 was purified by absorption on anti-p85–protein A–Sepharose beads and mixed with p110α, and lipid kinase activity was determined. All determinations were made in triplicate, and the data are the means ± standard errors of the means of two separate experiments.