Mutations in the mitochondrial ATP synthase gamma subunit suppress a slow-growth phenotype of yme1 yeast lacking mitochondrial DNA.

In Saccharomyces cerevisiae, inactivation of the nuclear gene YME1 causes several phenotypes associated with impairment of mitochondrial function. In addition to deficiencies in mitochondrial compartment integrity and respiratory growth, yme1 mutants grow extremely slowly in the absence of mitochondrial DNA. We have identified two genetic loci that, when mutated, act as dominant suppressors of the slow-growth phenotype of yme1 strains lacking mitochondrial DNA. These mutations only suppressed the slow-growth phenotype of yme1 strains lacking mitochondrial DNA and had no effect on other phenotypes associated with yme1 mutations. One allele of one linkage group had a collateral respiratory deficient phenotype that allowed the isolation of the wild-type gene. This suppressing mutation was in ATP3, a gene that encodes the gamma subunit of the mitochondrial ATP synthase. Recovery of two of the suppressing ATP3 alleles and subsequent sequence analysis placed the suppressing mutations at strictly conserved residues near the C terminus of Atp3p. Deletion of the ATP3 genomic locus resulted in an inability to utilize nonfermentable carbon sources. atp3 deletion strains lacking mitochondrial DNA grew slowly on glucose media but were not as compromised for growth as yme1 yeast lacking mitochondrial DNA.