SUPPRESSION OF RHO(0) LETHALITY BY MITOCHONDRIAL ATP SYNTHASE F-1 MUTATIONS IN KLUYVEROMYCES-LACTIS OCCURS IN THE ABSENCE OF F-0

Specific mgi mutations in the alpha, beta or gamma subunits of the mit ochondrial F-1-ATPase have previously been found to suppress rho(0) le thality in the petite-negative yeast Kluyveromyces lactis. To determin e 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 Kl ATP4, 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 respi ration deficient and have reduced viability. However a strain devoid o f the three nuclear genes is still unable to lose mitochondrial DNA, w hereas a mgi mutant with the three genes inactivated remains petite-po sitive. In the latter case, rho(0) mutants can be isolated, upon treat ment with ethidium bromide, that lack six major F-0 subunits, namely t he nucleus-encoded subunits b, OSCP and d, and the mitochondrially enc oded 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 s ubunits and that suppression of rho(0) lethality is an intrinsic prope rty of the altered F-1 particle.