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 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.
Davis-Kaplan
Sandra R
SR
Division of Immunology and Cell Biology, Department of Pathology, School of Medicine, University of Utah, Salt Lake City, Utah 84132-2501, USA.
Compton
Mark A
MA
Flannery
Andrew R
AR
Ward
Diane M
DM
Kaplan
Jerry
J
Stevens
Tom H
TH
Graham
Laurie A
LA
D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D004721:Endoplasmic Reticulum / Q000201:enzymology / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry*; D017353:Gene Deletion; D007425:Intracellular Membranes / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry* / Q000502:physiology; D018832:Molecular Chaperones; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000502:physiology; D017386:Sequence Homology, Amino Acid; D025262:Vacuolar Proton-Translocating ATPases / Q000378:metabolism / Q000502:physiology*; D014617:Vacuoles / Q000378:metabolism
D005656:Fungal Proteins; D008565:Membrane Proteins; D018832:Molecular Chaperones; C515120:PKR1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D025262:Vacuolar Proton-Translocating ATPases