A PHOSPHATIDYLINOSITOL 3-KINASE AND PHOSPHATIDYLINOSITOL TRANSFER PROTEIN ACT SYNERGISTICALLY IN FORMATION OF CONSTITUTIVE TRANSPORT VESICLES FROM THE TRANS-GOLGI NETWORK

Current evidence suggests that phosphatidylinositol (PI) kinases and p hosphatidylinositol transfer protein (PITP) are involved in driving ve sicular traffic from yeast and mammalian trans-Golgi network (TGN). We have tested the interaction between these cytosolic proteins in an as say that measures the formation of constitutive transport vesicles fro m the TGN in a hepatocyte cell-free system. This reaction is dependent on a novel PI 3-kinase, and we now report that, under conditions of l imiting cytosol, purified PI 3-kinase and PITP functionally cooperate to drive exocytic vesicle formation. This synergy was observed with bo th yeast and mammalian PITPs, and it also extended to the formation of PI 3-phosphate. These collective findings indicate that the PI 3-kina se and PITP synergize to form a pool of PI 3-phosphate that is essenti al for formation of exocytic vesicles from the hepatocyte TGN.