Subunit C of the Vacuolar-Type ATPase from the Vanadium-Rich Ascidian, Ascidia sydneiensis samea, Rescued the pH Sensitivity of Yeast vma5 Mutants
A vanadium-accumulating ascidian, Ascidia sydneiensis samea, expresses vacuolar-type H+-ATPases (V ATPases) on the vacuole membrane of the vanadium-containing blood cells known as vanadocytes. Previously, we showed that the contents of their vacuoles are extremely acidic and that a V ATPase-specific inhibitor, bafilomycin A1, neutralized the contents of the vacuoles. To understand the function of V ATPase in vanadocytes, we isolated cDNA encoding subunit C of V ATPase from vanadocytes since this subunit has been known to be responsible for the assembly of V-ATPases and to regulate the ATPase activity of V-ATPases. The cloned cDNA was 1,443 nucleotides in length, and encoded a putative 384 amino-acid protein. By expressing the ascidian cDNA for subunit C under the control of a galactose-inducible promoter, the pH-sensitive phenotype of the corresponding vma5 mutant of a budding yeast was rescued. This result showed that the ascidian cDNA for subunit C functioned in yeast cells.
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