HUMAN PHOSPHATIDYLINOSITOL 3-KINASE COMPLEX RELATED TO THE YEAST VPS34P-VPS15P PROTEIN SORTING SYSTEM

Phosphoinositide (PI) 3-kinases have been characterized as enzymes inv olved in receptor signal transduction in mammalian cells and in a comp lex which mediates protein trafficking in yeast, PI 3-kinases linked t o receptors with intrinsic or associated tyrosine kinase activity are heterodimeric proteins, consisting of p85 adaptor and p110 catalytic s ubunits, which can generate the 3-phosphorylated forms of phosphatidyl inositol (PtdIns), PtdIns4P and PtdIns(4,5)P-2 as potential second mes sengers, Yeast Vps34p kinase, however, has a substrate specificity res tricted to PtdIns and is a PtdIns 3-kinase, Here the molecular charact erization of a new human PtdIns 3-kinase with extensive sequence homol ogy to Vps34p is described, PtdIns 3-kinase does not associate with p8 5 and phosphorylates PtdIns, but not PtdIns4P or PtdIns(4,5)P-2. In vi vo PtdIns 3-kinase is in a complex with a cellular protein of 150 kDa, as detected by immunoprecipitation from human cells, Protein sequence analysis and cDNA cloning show that this 150 kDa protein is highly ho mologous to Vps15p, a 160 kDa protein serine/threonine kinase associat ed with yeast Vps34p, These results suggest that the major components of the yeast Vps intracellular trafficking complex are conserved in hu mans.