Suppression of ρ0 lethality by mitochondrial ATP synthase F1 mutations in Kluyveromyces lactis occurs in the absence of F0

Specific mgi mutations in the alpha, beta or gamma subunits of the mitochondrial F-1-ATPase have previously been found to suppress rho(0) lethality in the petite-negative yeast Kluyveromyces lactis. To determine whether the suppressive activity of the altered F-1 is dependent on the F-0 sector of ATP synthase, we isolated and disrupted the genes KlATP4, 5 and 7, the three nuclear genes encoding subunits b, OSCP and d. Strains disrupted for any one, or all three of these genes are respiration deficient and have reduced viability. However a strain devoid of the three nuclear genes is still unable to lose mitochondrial DNA, whereas a mgi mutant with the three genes inactivated remains petite-positive. In the latter case, rho(0) mutants can be isolated, upon treatment with ethidium bromide, that lack six major F-0 subunits, namely the nucleus-encoded subunits b, OSCP and d, and the mitochondrially encoded Atp6, 8 and 9p. Production of rho(0) mutants indicates that an F-1-complex carrying a mgi mutation can assemble in the absence of F-0 subunits and that suppression of rho(0) lethality is an intrinsic property of the altered F-1 particle.