Abstract
Previous purification and characterization of the yeast vacuolar proton-translocating ATPase (H(+)-ATPase) have indicated that it is a multisubunit complex consisting of both integral and peripheral membrane subunits (Uchida, E., Ohsumi, Y., and Anraku, Y. (1985) J. Biol. Chem. 260, 1090-1095; Kane, P. M., Yamashiro, C. T., and Stevens, T. H. (1989) J. Biol. Chem. 264, 19236-19244). We have obtained monoclonal antibodies recognizing the 42- and 100-kDa polypeptides that were co-purified with vacuolar ATPase activity. Using these antibodies we provide further evidence that the 42-kDa polypeptide, a peripheral membrane protein, and the 100-kDa polypeptide, an integral membrane protein, are genuine subunits of the yeast vacuolar H(+)-ATPase. The synthesis, assembly, and targeting of three of the peripheral subunits (the 69-, 60-, and 42-kDa subunits) and two of the integral membrane subunits (the 100- and 17-kDa subunits) were examined in mutant yeast cells containing chromosomal deletions in the TFP1, VAT2, or VMA3 genes, which encode the 69-, 60-, and 17-kDa subunits, respectively. The steady-state levels of the various subunits in whole cell lysates and purified vacuolar membranes were assessed by Western blotting, and the intracellular localization of the 60- and 100-kDa subunits was also examined by immunofluorescence microscopy. The results suggest that the assembly and/or the vacuolar targeting of the peripheral subunits of the yeast vacuolar H(+)-ATPase depend on the presence of all three of the 69-, 60-, and 17-kDa subunits. The 100-kDa subunit can be transported to the vacuole independently of the peripheral membrane subunits as long as the 17-kDa subunit is present; but in the absence of the 17-kDa subunit, the 100-kDa subunit appears to be both unstable and incompetent for transport to the vacuole.
Highlights
Polypeptides that were co-purified with vacuAolTaPr- binding catalytic site; the 17-kDa subunit is thought to form ase activity
The resultssuggest that theassembly and/or but subsequent studies revealed that eight polypeptides, of the vacuolar targetinogf the peripheral subuniotfsthe apparent molecular masses 100, 69, 60, 42, 36, 32, 27, and 17 yeast vacuolar H+-ATPase depend on the presenceof all three of the 69, 60, and 17-kDa subunits
100-kDa subunit can be transported to the vacuole independently of the peripheral membrane subuniats long as the 17-kDa subunit is present; but in the abkDa, co-purified with ATPase activity when the enzyme was isolated by glycerol gradient centrifugation (Kaneet al., 1989)
Summary
Polypeptides that were co-purified with vacuAolTaPr- binding catalytic site; the 17-kDa subunit is thought to form ase activity. Of the Yeast Vacuolar H+-ATPase membranes were pelleted by centrifugation in aBeckman Ti-80 rotor antibody against the 69-kDa subunit detected this subunit in a t 175,000 X g for 3 ha t 4 "C.
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