ALLELE-SPECIFIC EXPRESSION OF THE MGI(-) PHENOTYPE ON DISRUPTION OF THE F1-ATPASE DELTA-SUBUNIT GENE IN KLUYVEROMYCES-LACTIS

Kluyveromyces lactis is a petite-negative yeast that does not form via ble mitochondrial genome-deletion mutants (petites) when treated with DNA-targeting drugs. Loss of mtDNA is lethal for this yeast but mutati ons at three loci termed MG1, for mitochondrial genome integrity, can suppress this lethality. The three loci encode the alpha-, beta- and g amma-subunits of mitochondrial F-1-ATPase. In this study we report the isolation and characterization of the K1ATP delta gene encoding the d elta-subunit of F-1-ATPase. The deduced protein contains 158 amino aci ds showing 72% identity to the protein from Saccharomyces cerevisiae a nd a putative mitochondrial targeting sequence of 23 amino acids. Disr uption of the gene causes cells to become respiratory deficient while the introduction of ATP delta from S. cerevisiae restores growth on gl ycerol, Cells with a disrupted ATP delta gene, like strains with disru ptions of alpha-, beta- and gamma-F-1-subunits, do not produce petite mutants when treated with ethidium bromide. However, unlike strains wi th disruptions in the three largest F-1-subunits, disruption of ATP de lta in the presence of some mgi alleles does not abolish the Mgi(-) ph enotype. By contrast, elimination of ATP delta in other mgi strains re moves resistance to ethidium bromide and rho(0) mutants are not formed , Hence the ATP delta subunit of F-1-ATPase, while not mandatory for a Mgi(-) phenotype,aids some mgi alleles in suppressing rho(0) lethalit y.