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J. Biol. Chem., Vol. 281, Issue 42, 32025-32035, October 20, 2006

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PKR1 Encodes an Assembly Factor for the Yeast V-Type ATPase^*

Sandra R. Davis-Kaplan¹, Mark A. Compton, Andrew R. Flannery, Diane M. Ward, Jerry Kaplan², Tom H. Stevens³, and Laurie A. Graham¹

From the Division of Immunology and Cell Biology, Department of Pathology, School of Medicine, University of Utah, Salt Lake City, Utah 84132-2501 and the Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403-1229

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 pkr1 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.

Received for publication, July 6, 2006 , and in revised form, August 7, 2006.

^* This work was supported by National Institutes of Health Grants GM38006 (to T. H. S.) and DK30534 (to J. K.), and support for DNA oligonucleotides and sequencing was provided by Cancer Center Support Grant CA43014. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Both authors contributed equally to this work.

² To whom correspondence may be addressed. Tel.: 801-581-7427; Fax: 801-581-6001; E-mail: jerry.kaplan{at}path.utah.edu. ³ To whom correspondence may be addressed. Tel.: 541-346-5884; Fax: 541-346-4854; E-mail: stevens{at}molbio.uoregon.edu.

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