P110-DELTA, A NOVEL PHOSPHATIDYLINOSITOL 3-KINASE CATALYTIC SUBUNIT THAT ASSOCIATES WITH P85 AND IS EXPRESSED PREDOMINANTLY IN LEUKOCYTES

We have identified a novel p110 isoform of phosphatidylinositol 3-kina se from human leukocytes that we have termed p110 delta, In addition, we have independently isolated p110 delta from a mouse embryo library on the basis of its ability to interact with Ha-Ras(V12) in the yeast two-hybrid system, This unique isoform contains all of the conserved s tructural features characteristic of the p110 family, Recombinant p110 delta phosphorylates phosphatidylinositol and coimmunoprecipitates wi th p85, However, in contrast to previously described p110 subunits, p1 10 delta is expressed in a tissue-restricted fashion; it is expressed at high levels in lymphocytes and lymphoid tissues and may therefore p lay a role in phosphatidylinositol 3-kinase-mediated signaling in the immune system.