Osh-dependent and -independent Regulation of PI4P Levels During Polarized Growth of Saccharomyces cerevisiae

Abstract

For polarized secretion to occur, secretory vesicles must mature to a docking-competent state. In current models, an OSBP-related protein, Osh4p, modulates vesicle-associated PI4P levels along the secretory pathway. Utilizing the lipid-binding domain P4M and live-cell imaging of Saccharomyces cerevisiae we showed that, contrary to existing models, vesicle-associated PI4P levels remain constant as vesicles traffic from the TGN to the PM. Furthermore, all members of the Osh protein family play a role in maintaining intracellular PI4P distribution. We propose a new model for polarized secretion by S. cerevisiae in which vesicular PI4P levels remain constant in an Osh4p-independent manner.