Within the mitochondrial F1Fo-ATP synthase, the nuclear-encoded delta F1 subunit plays a critical role in coupling the enzyme proton translocating and ATP synthesis activities. In Saccharomyces cerevisiae, deletion of the delta subunit gene (Deltadelta) was shown to result in a massive destabilization of the mitochondrial genome (mtDNA) in the form of 100% rho-/rho degrees petites, i.e. cells missing a large portion (>50%) of the mtDNA (rho-) or totally devoid of mtDNA (rho degrees ). Previous work has suggested that the absence of complete mtDNA (rho+) in Deltadelta yeast is a consequence of an uncoupling of the ATP synthase in the form of a passive proton transport through the enzyme, i.e. not coupled to ATP synthesis. However it was unclear why or how this ATP synthase defect destabilized the mtDNA. We investigated this question using a non respiratory gene (ARG8m) inserted into the mtDNA. We first show that retention of functional mtDNA is lethal to Deltadelta yeast. We further show that combined to a nuclear mutation (Deltaatp4) preventing the ATP synthase proton channel assembly, a lack in delta subunit fails to destabilize the mtDNA and rho+ Deltadelta cells become viable. We conclude that Deltadelta yeast cannot survive when it has the ability to synthesize the ATP synthase proton channel. Accordingly, the rho-/rho degrees mutation can be viewed as a rescuing event because this mutation prevents the synthesis of the two mtDNA encoded subunits (Atp6p and Atp9p) forming the core of this channel. This is the first report of what we have called a 'petite-obligate' mutant of S. cerevisiae.
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|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Phenotype||Experiment Type||Experiment Type Category||Mutant Information||Strain Background||Chemical||Details||Reference|
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