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doi: 10.1242/10.1242/jcs.00328

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Role of the Vtc proteins in V-ATPase stability and membrane trafficking

Friedrich-Miescher-Laboratorium der Max-Planck-Gesellschaft, Spemannstr. 37-39, 72076 Tübingen, Germany

^* Author for correspondence (e-mail: Andreas.Mayer{at}Tuebingen.mpg.de)

Accepted 17 December 2002

Vtc proteins have genetic and physical relations with the vacuolar H⁺-ATPase (V-ATPase), influence vacuolar H⁺ uptake and, like the V-ATPase V₀ sectors, are important factors in vacuolar membrane fusion. Vacuoles from vtc1 and vtc4 mutants had slightly reduced H⁺-uptake activity. These defects could be separated from Vtc function in vacuole fusion, demonstrating that Vtc proteins have a direct role in membrane fusion. We analyzed their involvement in other membrane trafficking steps and in VATPase dynamics. Deletion of VTC genes did not impede endocytic trafficking to the vacuole. However, ER to Golgi trafficking and further transport to the vacuole was delayed in vtc3 cells. In accordance with that, vtc3 cells showed a reduced growth rate. Vtc mutations did not interfere with regulated assembly and disassembly of the V-ATPase, but they affected the number of peripheral V₁ subunits associated with the vacuoles. vtc3 vacuoles carried significantly more V₁ subunits, whereas vtc1, vtc2 and vtc4 had significantly less. The proteolytic sensitivity of the V₀ subunit Vph1p was different in vtc and wild-type cells in vivo, corroborating the physical interaction of Vtc proteins with the V-ATPase observed in vitro. We suggest that Vtc proteins affect the conformation of V₀. They might thereby influence the stability of the VATPase holoenzyme and support the function of its V₀ sector in vacuolar membrane fusion.

Key words: Membrane fusion, NSF, Saccharomyces cerevisiae, SNARE, Vacuole, Yeast

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