Essential role for diacylglycerol in protein transport from the yeast Golgi complex

Abstract

Yeast phosphatidylinositol transfer protein (Secl4p) is required for the production of secretory vesicles from the Golgi. This requirement can be relieved by inactivation of the cytosine 5'diphosphate (CDP)-choline pathway for phosphatidy1choline biosynthesis, indicating that Secl4p is an essential component of a regulatory pathway linking phospholipid metabolism with vesicle trafficking (the Secl4p pathway1-6). Sac1p (refs 7 and 8) is an integral membrane protein related to inositol-5-phosphatases such as synaptojanin9, a protein found in rat brain. Here we show that defects in Sac1p also relieve the requirement for Secl4p by altering phospholipid metabolism so as to expand the pool of diacylglycerol (DAG) in the Golgi. Moreover, although shortchain DAG improves secretory function in strains with a temperature-sensitive Secl4p, expression of diacylglycerol kinase from Escherichia coli further impairs it. The essential function of Sec14p may therefore be to maintain a sufficient pool of DAG in the Golgi to support the production of secretory vesicles.