FIG. 2.

Expression of PI 3-Kα and PI 3-Kβ in NIH 3T3 cells (A) and in BI-141 lymphoid T cells (C). PI 3-Kα and PI 3-Kβ were immunoprecipitated from cell lysates by using nonimmune rabbit serum (NRS) or anti-PI 3-K sera as indicated followed by an in vitro PI 3-K assay using PI(4,5)P₂ as a substrate. Products were resolved on thin-layer chromatography plates. The presence of p85α in the immunocomplex is also shown and was determined by Western blotting analysis using anti-p85a antibody. (B) Association of p85α subunit with p110α and p110β in NIH 3T3 cells. Fibroblast lysate was immunodepleted of p110α and p110β molecules by using a mixture of αp110α.1 and αp110β.3 or nonimmune serum as indicated. The presence of p85α was detected as described for panel A. p85α was also immunoprecipitated from depleted cell lysates followed by an in vitro PI 3-K assay using PI–PI(4)P–PI(4,5)P₂ (1:1:1) as substrates. Shown are the labelled products that were resolved by thin-layer chromatography. The positions of phosphatydylinositol phosphate (PIP), PIP₂, PIP₃, and the origin (Ori) are shown. ip, immunoprecipitate.