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Volume 272, Number 42, Issue of October 17, 1997 pp. 26787-26793
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.

V₁-situated Stalk Subunits of the Yeast Vacuolar Proton-translocating ATPase

(Received for publication, May 30, 1997, and in revised form, July 29, 1997)

John J. Tomashek , Laurie A. Graham ^§ , Maria U. Hutchins , Tom H. Stevens ^§ and Daniel J. Klionsky

From the  Section of Microbiology, University of California, Davis, California 95616 and the ^§ Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403

The proton-translocating ATPase of the yeast vacuole is an enzyme complex consisting of a large peripheral membrane sector (V₁) and an integral membrane sector (V₀), each composed of multiple subunits. The V₁ sector contains subunits that hydrolyze ATP, whereas the V₀ sector contains subunits that translocate protons across the membrane. Additional subunits in both sectors couple these activities. Here we have continued our examination of intermediate subunits primarily associated with the V₁ but also implicated in interactions with the V₀. Interactions between Vma7p (F) and Vma8p (D) and between Vma4p (E) and Vma10p (G) are described. Although Vma7p and Vma10p have been observed to interact with the V₀ sector, our results indicate that these subunits behave primarily as canonical V₁ sector subunits. We categorize these four subunits as "stalk" subunits to distinguish them from the known catalytic (A and B) and proton-translocating (c, c, and Vma16p) subunits and to highlight their intermediate nature. Furthermore, we show that the in vivo stability of Vma4p is dependent upon interaction with Vma10p. This may be important in the regulation of assembly, since these two subunits add to the V₁ during later stages of V₁ assembly. This is the first demonstration of interdependence between ATPase subunits for structural stability.

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