IDENTIFICATION OF A PHOSPHATIDYLINOSITOL 3-HYDROXY KINASE IN PLANT-CELLS - ASSOCIATION WITH THE CYTOSKELETON

Radiolabelling experiments have revealed that plant cells contain the two 3-phosphorylated phosphoinositides: PtdIns3P and PtdIns(3,4)P-2 [B rearley and Hanke (1992) Biochem. J. 283, 255-260]. However, nothing i s known about the enzymes involved in the metabolism of these plant 3- phosphorylated phosphoinositides. In this study we demonstrate the pre sence of a PtdIns 3-hydroxy kinase(s) in plant cells. This activity wa s enriched in the cytoskeletal fraction whereas only low levels of pho sphoinositide 3-hydroxy kinase could be detected in plasma membranes a nd microsomal preparations. This cytoskeletal phosphoinositide 3-hydro xy kinase was found to be wortmannin insensitive and thus resembles Pt dIns-specific 3-hydroxy kinases of which vps34p is one example.