PKR1 Encodes an Assembly Factor for the Yeast V-Type ATPase.
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 V(0) subunit or an endoplasmic reticulum (ER) assembly factor. However, unlike yeast mutants lacking a V(0) 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.[1]References
- PKR1 Encodes an Assembly Factor for the Yeast V-Type ATPase. Davis-Kaplan, S.R., Compton, M.A., Flannery, A.R., Ward, D.M., Kaplan, J., Stevens, T.H., Graham, L.A. J. Biol. Chem. (2006) [Pubmed]
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