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Biochem Biophys Res Commun. 1992 Oct 15;188(1):40-7.

Mutations at the putative junction sites of the yeast VMA1 protein, the catalytic subunit of the vacuolar membrane H(+)-ATPase, inhibit its processing by protein splicing.

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  • 1Department of Biology, Faculty of Science, University of Tokyo, Japan.


A single gene, VMA1, encodes the 69-kDa subunit of the vacuolar membrane H(+)-ATPase in the yeast Saccharomyces cerevisiae. We have proposed that the subunit is synthesized as a precursor of 120 kDa (1,071 amino acids) and then converted to the 69-kDa form by an unusual processing reaction, which removes the internal domain of 454 amino acids (residues 284-737) and joins the N- and C-terminal domains. Cysteine to serine mutations at residues 284 and 738, the residues that bracket the internal domain, were introduced into the VMA1 gene by site-directed mutagenesis, and the mutant genes were expressed in a null vma1 mutant. Cells harboring either of the mutant vma1 genes accumulate nonfunctional fragments of the subunit. The mutation of Cys-284 inhibited the cleavage of the N-terminal junction site. Cys-738-->Ser mutation appeared to block the processing at both junction sites although the mutant gene yielded a small fraction of the functional 69-kDa subunit.

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