VMA7 ENCODES A NOVEL 14-KDA SUBUNIT OF THE SACCHAROMYCES-CEREVISIAE VACUOLAR H-ATPASE COMPLEX()

The Saccharomyces cerevisiae vacuolar proton-translocating ATPase (V-A TPase) is composed of at least 10 subunits belonging to either the per ipheral V-1 or integral membrane V-0 subcomplex. We have characterized a novel 14-kDa V-ATPase subunit (Vma7p), encoded by the VMA7 gene, wh ich exhibits features common to both V-1 and V-0 subunit proteins. Vma 7p is a hydrophilic protein of 118 amino acids with a predicted molecu lar mass of 13,452 Da. Vacuolar membranes isolated from a vma7 Delta n ull mutant contained no V-ATPase activity. Western analysis of vma7 De lta cells revealed greatly reduced levels of the remaining V-0 complex V-ATPase subunits, but normal levels of the V-1 subunits. However, th e V-1 subunits failed to associate with the vacuolar membrane. Unlike the integral membrane subunits of the V-0 complex, Vma7p was easily st ripped from vacuolar membranes. Density gradient fractionation reveale d that Vma7p associated only with the fully assembled V-ATPase and did not associate with a separate lower density V-0 subcomplex fraction. The unique properties of the Vma7p may reflect a critical role in stab ilizing the V-0 complex and bridging the V-1 and V-0 complexes to form a functional V-ATPase complex.