The Role of Ubx2p in ER-Resident Protein Retention

Abstract

Protein folding in the endoplasmic reitculum (ER) happens with the help of ER-resident proteins called chaperones. However, when UBX2 is deleted in Saccharomyces cerevisiae, some of these chaperones, namely Kar2p and Pdi1p, are secreted outside the cell at uncommonly high levels. This is noteworthy since none of the other proteins involved in Ubx2p’s primary known function demonstrate the same secretion phenotype when deleted. Ubx2p is also known to regulate desaturated lipids in the cell’s membranes, so in order to investigate this unusual secretion phenotype, ubx2Δ mutant cells, WT cells, and ubx2Δ transformed with either full-length UBX2 or a construct lacking one of its two primary domains were assayed for secretion of chaperone proteins after growth on YPD and YPD with oleate. Oleate reduced differences in chaperone secretion between ubx2Δ and WT cells, suggesting that it is Ubx2p’s role in lipid regulation that results in the secretion defect when it is removed.