Yeast vacuoles contain an H+-ATPase that acidifies the vacuolar lumen and generates an electrochemical gradient of protons across their membranes. Five polypeptides, denoted as subunits A to E in the order of decreasing molecular masses from 69 to 27 kDa, were identified in the catalytic sector of the enzyme. However, other polypeptides may be necessary for the activity of the enzyme. When a 14-kDa polypeptide was suggested to be a subunit of a specialized V-ATPase in Manduca sexta, and a homologous short sequence was detected downstream of the UGA1 gene in yeast, we cloned this counterpart gene from yeast. The gene VMA7 encodes a protein Vma7p of about 14 kDa. The predicted protein is highly homologous to the above mentioned M. sexta protein. The Δvma7::URA3 null mutant exhibits growth characteristics typical of other VMA disruptant mutants in genes encoding subunits of the catalytic sector. The Δvma7::URA3 null mutants are not able to grow on a medium buffered at pH 7.5, they fail to accumulate quinacrine into their vacuoles and the other subunits of the catalytic sector are not assembled onto the vacuolar membrane in its absence. Epitope-tagged Vma7p was constructed and the proton uptake activity of isolated vacuoles from this yeast strain was markedly inhibited by a monoclonal antibody against the epitope-tag. A cold inactivation experiment demonstrated that Vma7p is a genuine subunit of the catalytic sector of V-ATPase and it is denoted as subunit F.
|Number of pages||6|
|Journal||Journal of Biological Chemistry|
|State||Published - 30 Sep 1994|