SUBUNIT COMPOSITION, BIOSYNTHESIS, AND ASSEMBLY OF THE YEAST VACUOLAR PROTON-TRANSLOCATING ATPASE

The yeast vacuole is acidified by a vacuolar proton-translocating ATPase (H+-ATPase) that closely resembles the vacuolar H+-ATPases of other fungi, animals, and plants. The yeast enzyme is purified as a complex of eight subunits, which include both integral and peripheral membrane proteins. The genes for seven of these subunits have been cloned, and mutant strains lacking each of the subunits (vma mutants) have been constructed. Disruption of any of the subunit genes appears to abolish the function of the vacuolar H+-ATPase, supporting the subunit composition derived from biochemical studies. Genetic studies of vacuolar acidification have also revealed an additional set of gene products that are required for vacuolar H+-ATPase activity, but may not be part of the final enzyme complex. The biosynthesis, assembly, and targeting of the enzyme is being elucidated by biochemical and cell biological studies of the vma mutants. Initial results suggest that the peripheral and integral membrane subunits may be independently assembled.