Localization of Lipid Raft Proteins to the Plasma Membrane Is a Major Function of the Phospholipid Transfer Protein Sec14

The Sec14 protein domain is a conserved tertiary structure that binds hydrophobic ligands. The Sec14 protein from Saccharomyces cerevisiae is essential with studies of S. cerevisiae Sec14 cellular function facilitated by a sole temperature sensitive allele, sec14^ts. The sec14^ts allele encodes a protein with a point mutation resulting in a single amino acid change, Sec14^G266D. In this study results from a genome-wide genetic screen, and pharmacological data, provide evidence that the Sec14^G266D protein is present at a reduced level compared to wild type Sec14 due to its being targeted to the proteosome. Increased expression of the sec14^ts allele ameliorated growth arrest, but did not restore the defects in membrane accumulation or vesicular transport known to be defective in sec14^ts cells. We determined that trafficking and localization of two well characterized lipid raft resident proteins, Pma1 and Fus-Mid-GFP, were aberrant in sec14^ts cells. Localization of both lipid raft proteins was restored upon increased expression of the sec14^ts allele. We suggest that a major function provided by Sec14 is trafficking and localization of lipid raft proteins.