Biogenesis of mitochondria: DNA sequence analysis of mit− mutations in the mitochondrial oli2 gene coding for mitochondrial ATPase subunit 6 in Saccharomyces cerevisiae

A series of yeast mitochondrial, mit− mutants with defects in the oli2 gene, coding for subunit 6 of the mitochondrial ATPase complex, has been analyzed at the DNA sequence level. Fifteen of sixteen primary mit− mutants were shown to contain frameshift or nonsense mutations predicting truncated subunit 6 polypeptides, in various strains ranging from about 20% to 95% of the wild-type length of 259 amino acids. In only one strain could the defect in subunit 6 function be assigned to amino acid substitution in an otherwise full-length subunit 6. Many mutants carried multiple base substitutions or insertions/deletions, presumably arising from the manganese chloride mutagenesis treatment. Revertants fron three of the mit− mutants were analyzed: all contained full-length subunit 6 proteins with one or more amino acid substitutions. The preponderance of truncated proteins as opposed to substituted full-length proteins in oli8 mit− mutants is suggested to reflect the ability of subunit 6 to accommodate amino acid substitutions at many locations, with little or no change in its functional properties in the membrane Fo-sector of the ATPase complex.