The yeast phosphatidylinositol transfer protein (Sec14p) is required for biogenesis of Golgi‐derived transport vesicles and cell viability, and this essential Sec14p requirement is abrogated by inactivation of the CDP‐choline pathway for phosphatidylcholine biosynthesis. These findings indicate that Sec14p functions to alleviate a CDP‐choline pathway‐mediated toxicity to yeast Golgi secretory function. We now report that this toxicity is manifested through the action of yeast Kes1p, a polypeptide that shares homology with the ligand‐binding domain of human oxysterol binding protein (OSBP). Identification of Kes1p as a negative effector for Golgi function provides the first direct insight into the biological role of any member of the OSBP family, and describes a novel pathway for the regulation of Golgi‐derived transport vesicle biogenesis.

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