CLONING OF THE YEAST ATP3 GENE CODING FOR THE GAMMA-SUBUNIT OF F1 ANDCHARACTERIZATION OF ATP3 MUTANTS

Saccharomyces cerevisiae pet mutants, of complementation group G115, a re deficient in mitochondrial ATPase and have properties indicative of defective F-1. In this study we show that C287/LU1, a mutant belongin g to group G115, is complemented by the yeast nuclear ATP3 gene coding for the gamma-subunit of the mitochondrial F-1- ATPase. The amino-ter minal sequence of the mature gamma-subunit matches the sequence encode d by ATP3 starting with the 34th amino acid confirming the identity of the gene, and earlier evidence indicating that this F-1 component is synthesized as a precursor with a long amino-terminal extension.The pr operties of the mitochondrial ATPase have been studied in C287/LU1 wit h an Ala(273) --> Val substitution in the carboxyl-terminal region of the gamma-subunit and in W303 Delta ATP3, a mutant lacking the gamma-s ubunit as a result of a deletion in ATP3. Both strains have negligible ATPase activity but near normal concentrations of the alpha- and beta -subunits of F-1. In W303 Delta ATP3, the subunits do not form a stabl e F-1 oligomer nor are they firmly associated with F-0. This is not tr ue of C287/LU1, which was found to assemble an F-1-F-0 complex. These data indicate that the yeast gamma-subunit has dual functions, one in catalysis of ATP hydrolysis/synthesis and the second in assembly/stabi lity of F-1.