Division of Immunology and Cell Biology, Department of Pathology, School of Medicine, University of Utah, Salt Lake City, Utah 84132-2501, USA-
Abstract: Deletion of the yeast gene PKR1 -YMR123W- results in an inability to grow on iron-limited medium- Pkr1p is localized to the membrane of the endoplasmic reticulum- Cells lacking Pkr1p show reduced levels of the V-ATPase subunit Vph1p due to increased turnover of the protein in mutant cells- Reduced levels of the V-ATPase lead to defective copper loading of Fet3p, a component of the high affinity iron transport system- Levels of Vph1p in cells lacking Pkr1p are similar to cells unable to assemble a functional V-ATPase due to lack of a V0 subunit or an endoplasmic reticulum -ER- assembly factor- However, unlike yeast mutants lacking a V0 subunit or a V-ATPase assembly factor, low levels of Vph1p present in cells lacking Pkr1p are assembled into a V-ATPase complex, which exits the ER and is present on the vacuolar membrane- The V-ATPase assembled in the absence of Pkr1p is fully functional because the mutant cells are able to weakly acidify their vacuoles- Finally, overexpression of the V-ATPase assembly factor Vma21p suppresses the growth and acidification defects of pkr1Delta cells- Our data indicate that Pkr1p functions together with the other V-ATPase assembly factors in the ER to efficiently assemble the V-ATPase membrane sector-