Vacuolar H(+)-ATPase: from mammals to yeast and back.

Vacuolar H(+)-adenosine triphosphatase (V-ATPase) is composed of distinct catalytic (V1) and membrane (V0) sectors containing several subunits. The biochemistry of the enzyme was mainly studied in organelles from mammalian cells such as chromaffin granules and clathrin-coated vesicles. Subsequently, mammalian cDNAs and yeast genes encoding subunits of V-ATPase were cloned and sequenced. The sequence information revealed the relation between V- and F-ATPase that evolved from a common ancestor. The isolation of yeast genes encoding subunits of V-ATPase opened an avenue for molecular biology studies of the enzyme. Because V-ATPase is present in every known eukaryotic cell and provides energy for vital transport systems, it was anticipated that disruption of genes encoding V-ATPase subunits would be lethal. Fortunately, yeast cells can survive the absence of V-ATPase by 'drinking' the acidic medium. So far only yeast cells have been shown to be viable without an active V-ATPase. In contrast to yeast, mammalian cells may have more than one gene encoding each of the subunits of the enzyme. Some of these genes encode tissue- and/or organelle-specific subunits. Expression of these specific cDNAs in yeast cells may reveal their unique functions in mammalian cells. Following the route from mammals to yeast and back may prove useful in the study of many other complicated processes.