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J. Biol. Chem., Vol. 282, Issue 11, 8521-8532, March 16, 2007

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Diploids Heterozygous for a vma13 Mutation in Saccharomyces cerevisiae Highlight the Importance of V-ATPase Subunit Balance in Supporting Vacuolar Acidification and Silencing Cytosolic V₁-ATPase Activity^*

Jason M. Rizzo, Maureen Tarsio, Gloria A. Martínez-Muñoz, and Patricia M. Kane¹

From the Department of Biochemistry and Molecular Biology, State University of New York Upstate Medical University, Syracuse, New York 13210 and the Department of Biology, Syracuse University, Syracuse, New York 13244

The V-ATPase H subunit (encoded by the VMA13 gene) activates ATP-driven proton pumping in intact V-ATPase complexes and inhibits MgATPase activity in cytosolic V₁ sectors (Parra, K. J., Keenan, K. L., and Kane, P. M. (2000) J. Biol. Chem. 275, 21761-21767). Yeast diploids heterozygous for a vma13 mutation show the pH- and calcium-dependent conditional lethality characteristic of mutants lacking V-ATPase activity, although they still contain one wild-type copy of VMA13. Vacuolar vesicles from this strain have 50% of the ATPase activity of those from a wild-type diploid but do not support formation of a proton gradient. Compound heterozygotes with a second heterozygous deletion in another V₁ subunit gene exhibit improved growth, vacuolar acidification, and ATP-driven proton transport in vacuolar vesicles. In contrast, compound heterozygotes with a second deletion in a V_o subunit grow even more poorly than the vma13 heterozygote, have very little vacuolar acidification, and have very low levels of V-ATPase subunits in isolated vacuoles. In addition, cytosolic V₁ sectors from this strain and from the strain containing only the heterozygous vma13 mutation have elevated MgATPase activity. The results suggest that balancing levels of subunit H with those of other V-ATPase subunits is critical, both for allowing organelle acidification and for preventing unproductive hydrolysis of cytosolic ATP.

Received for publication, July 26, 2006 , and in revised form, December 26, 2006.

^* This work was supported by National Institutes of Health Grant R01 GM50322 (to P. M. K.). 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 To whom correspondence should be addressed. Tel.: 315-464-8742; Fax: 315-464-8750; E-mail: kanepm{at}upstate.edu.

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