Phosphatidylinositolpolyphosphates (PIPs) are centrally involved in many biological
processes, ranging from cell growth and organization of the actin cytoskeleton to endo-and
exocytosis. Phosphorylation of phosphatidylinositol at the D-4 position, an essential step in
the biosynthesis of PIPs, appears to be catalyzed by two biochemically distinct enzymes.
However, only one of these two enzymes has been molecularly characterized. We now
describe a novel class of phosphatidylinositol 4-kinases that probably corresponds to the …