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Absence of the Mitochondrial AAA Protease Yme1p Restores F$_0$-ATPase Subunit Accumulation in an $oxa1$ Deletion Mutant of $Saccharomyces\ cerevisiae$

Abstract : The nuclear gene $OXA1$ encodes a protein located within the mitochondrial inner membrane that is required for the biogenesis of both cytochrome c oxidase (Cox) and ATPase. In the absence of Oxa1p, the translocation of the mitochondrially encoded subunit Cox2p to the intermembrane space (also referred to as export) is prevented, and it has been proposed that Oxa1p could be a component of a general mitochondrial export machinery. We have examined the role of Oxa1p in light of its relationships with two mitochondrial proteases, the matrix protease Afg3p-Rca1p and the intermembrane space protease Yme1p, by analyzing the assembly and activity of the Cox and ATPase complexes in $\Delta$$oxa1$, $\Delta$$oxa1$$\Delta$$afg3$, and $\Delta$$oxa1$$\Delta$$yme1$ mutants. We show that membrane subunits of both complexes are specifically degraded in the absence of Oxa1p. Neither Afg3p nor Yme1p is responsible for the degradation of Cox subunits. However, the F$_0$ subunits Atp4p, Atp6p, and Atp17p are stabilized in the $\Delta$$oxa1$$\Delta$$yme1$ double mutant, and oligomycin-sensitive ATPase activity is restored, showing that the increased stability of the ATPase subunits allows significant translocation and assembly to occur even in the absence of Oxa1p. These results suggest that Oxa1p is not essential for the export of ATPase subunits. In addition, although respiratory function is dispensable in $Saccharomyces\ cerevisiae$, we show that the simultaneous inactivation of AFG3 and YME1 is lethal and that the essential function does not reside in their protease activity.
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Claire Lemaire, Patrice Hamel, Jean Velours, Geneviève Dujardin. Absence of the Mitochondrial AAA Protease Yme1p Restores F$_0$-ATPase Subunit Accumulation in an $oxa1$ Deletion Mutant of $Saccharomyces\ cerevisiae$. Journal of Biological Chemistry, American Society for Biochemistry and Molecular Biology, 2000, 275 (31), pp.23471-23475. ⟨10.1074/jbc.m002045200⟩. ⟨cea-02473282⟩

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