Figure 2.

PI4KIIα accounts for the majority of PI(4)P-synthesizing activity in brain Triton X-100-soluble extracts. (A) Western blot analysis of total homogenates from mouse tissues with Abs directed against the proteins indicated. PI4KIIα is by far the predominant PI4KII expressed in brain. (B) Immunodepletion of PI4PKIIα from rat brain Triton X-100 extracts results in a dramatic reduction of PI 4-kinase activity. (Upper) Western blots for PI4KIIα and for the control protein amphiphysin 1 (Amph) in the starting material (SM), as well as in the corresponding extracts after immunoprecipitation with anti-PI4KIIα Ab, or with control IgGs. (Lower) The immunodepleted extract has lost nearly all PI kinase activity as revealed by TLC. Under our assay conditions, the bulk of PIP generated by the starting extract was found to be PI(4)P.