INCREASED EXPRESSION OF F1ATP SYNTHASE SUBUNITS IN YEAST STRAINS CARRYING POINT MUTATIONS WHICH DESTABILIZE THE BETA-SUBUNIT

In yeast strains (S. cerevisiae) carrying a point mutation of the ATP2 gene, which destabilizes the beta subunit of F1 ATP synthase in vitro , the growth rate was reduced significantly, demonstrating that the mu tation is also deleterious in vivo. Immunoblots showed that levels of the mutated beta, but also of the wild-type alpha subunit were increas ed in the mutated strains, together with levels of the corresponding m RNAs (approximately 1.6-fold). Northern analysis showed that this was due to both the appearance of new transcript species as well as upregu lation of the cognate transcripts, strongly indicating that the increa se was probably due to activation of transcription. Levels of other mi tochondrial proteins, e.g. cytochrome c oxidase, were unaffected. We c onclude that a specific signal communicates the actual performance of the ATP synthase inside the mitochondria to the nuclear genes encoding its subunits.