Assembly of the Mitochondrial Membrane System: Mutations in the pho2 Locus of the Mitochondrial Genome of Saccharomyces cerevisiae

Two mutants of Saccharomyces cerevisiae which show a loss of mitochondrial rutamycin‐sensitive ATPase activity are described. Although phenotypically similar to mutants of the mitochondrial locus pho1 [F. Foury and A. Tzagoloff (1976) Eur. J. Biochem. 68, 113–119], these mutants define a second ATPase locus on the mitochondrial DNA (designated pho2), which is genetically unlinked to pho1. Analysis of recombination in crosses involving multiple antibiotic resistance markers indicates that the locus is in the segment of the genome between ery1 and oli2, very close to oli1. In fact it is proposed that the oli1 and pho2 mutations are in the same gene. Supporting evidence for this proposal includes: The analysis of marker retention in petite mutants shows that the oli1 and pho2 loci were either retained or lost together in all cases. Recombination frequencies of 0.05% or less are observed in crosses between the oli1 and pho2 loci. When Q⁺ revertants are isolated from the pho2 mutants they frequently are oligomycin resistant. pho2 mutants have an altered subunit 9 of the ATPase complex.