Mutations in the Membrane Anchor of Yeast Cytochrome $c1$ Compensate for the Absence of Oxa1p and Generate Carbonate-Extractable Forms of Cytochrome $c1$

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Abstract : Oxa1p is a mitochondrial inner membrane protein that is mainly required for the insertion/assembly of complex IV and ATP synthase and is functionally conserved in yeasts, humans, and plants. We have isolated several independent suppressors that compensate for the absence of Oxa1p. Molecular cloning and sequencing reveal that the suppressor mutations ($CYT1-1\ to-6$) correspond to amino acid substitutions that are all located in the membrane anchor of cytochrome $c1$ and decrease the hydrophobicity of this anchor. Cytochrome $c1$ is a catalytic subunit of complex III, but the $CYT1-1$ mutation does not seem to affect the electron transfer activity. The double-mutant $cyt1-1,164$, which has a drastically reduced electron transfer activity, still retains the suppressor activity. Altogether, these results suggest that the suppressor function of cytochrome $c1$ is independent of its electron transfer activity. In addition to the membrane-bound cytochrome $c1$, carbonate-extractable forms accumulate in all the suppressor strains. We propose that these carbonate-extractable forms of cytochrome $c1$ are responsible for the suppressor function by preventing the degradation of the respiratory complex subunits that occur in the absence of Oxa1p.
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Patrice Hamel, Claire Lemaire, Nathalie Bonnefoy, Paule Brivet-Chevillotte, Geneviève Dujardin. Mutations in the Membrane Anchor of Yeast Cytochrome $c1$ Compensate for the Absence of Oxa1p and Generate Carbonate-Extractable Forms of Cytochrome $c1$. Genetics, Genetics Society of America, 1998, 150, pp.601-611. ⟨cea-02473320⟩

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