Osh4p is needed to reduce the level of phosphatidylinositol-4-phosphate on secretory vesicles as they mature.
Bottom Line: Phosphatidylinositol-4-phosphate (PI4P) is produced on both the Golgi and the plasma membrane.We show here that in yeast the oxysterol-binding proteins Osh1-Osh7 are collectively needed to maintain the normal distribution of PI4P and that Osh4p is critical in this function.This reduction in PI4P is necessary for a switch in the regulation of the Sec4p exchange protein, Sec2p, from an interaction with the upstream Rab, Ypt31/32, to an interaction with a downstream Sec4p effector, Sec15p.
Affiliation: Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, CA 92093.Show MeSH
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Mentions: In total, we propose that Osh4p is the principal Osh protein controlling the PI4P level of secretory vesicles. As the secretory vesicles move from Golgi to the plasma membrane, PI4P is turned over and/or extracted under the control of Osh4p (Figure 7). The decrease in the level of PI4P may facilitate the release of Ypt32p and recruitment of Sec15p to secretory vesicles. This mechanism is important for the subsequent assembly of exocyst and tethering of secretory vesicles in preparation for fusion to the plasma membrane.
Affiliation: Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, CA 92093.