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