The Phospholipid Transfer Protein Sec14 is Required for Trafficking from Endosomes and Regulates Distinct trans‐Golgi Export Pathways

Abstract

Vesicle fission, transport, and fusion are affected by membrane lipid composition. A protein known to regulate both lipid metabolism and vesicular transport is the phosphatidylcholine/phosphatidylinositol transfer protein Sec14 of Saccharomyces cerevisiae. We determined that decreasing Sec14 function affected secretion via the endosome dependent invertase route as well as the endosome independent route followed by Bgl2. Trafficking of a series of other secreted proteins including Hsp150, Cts1, Scw4, Scw10, Exg1, Cis3, and Ygp1 still occurred. Upon diminution of Sec14 function the v‐SNARE Snc1 accumulated in endosomes and the trans‐Golgi but was competent to traffic from the Golgi to the plasma membrane. Sec14 was required for trafficking of Ste3 and the lipophilic dye FM4‐64 from the plasma membrane to the vacuole at the level of endosomes. The results from a synthetic genetic array screen for genes whose inactivation impaired growth of cells with a temperature sensitive SEC14 allele, sec14ts, were consistent with Sec14 regulating endosome function. We go on to determine that lipid ligand occupancy by Sec14 can differentially regulate its functions. (Supported by CIHR and the Canada Research Chairs Fund)