The definition of mitochondrial H+ ATPase assembly defects in mit− mutants of Saccharomyces cerevisiae with a monoclonal antibody to the enzyme complex as an assembly probe

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 ⌬oxa1, ⌬oxa1⌬afg3, and ⌬oxa1⌬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 ⌬oxa1⌬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.

Section: Discussionsupporting

confidence: 83%

Absence of the Mitochondrial AAA Protease Yme1p Restores F0-ATPase Subunit Accumulation in an oxa1 Deletion Mutant of Saccharomyces cerevisiae

Lemaire¹,

Hamel²,

Velours³

et al. 2000

“…Thus, an increased expression of several or all genes of the ATP synthase might be necessary to regulate the abundance of the complex or, more likely, that regulation of complex abundance takes place on a translational or post-translationel level (18). Biogenesis of ATP synthases in eubacteria and mitochondria proceeds through assembly of the soluble F 1 followed by association to the transmembrane F 0 subcomplex (17,60). The independence of assembly of the two subcomplexes is abolished in plastids of the green algae Chlamydomonas where a concerted assembly of CF 1 and CF 0 subunits has been reported for mutants affected in different subunits (61)(62)(63).…”

Section: Discussionmentioning

confidence: 99%

Inactivation of the Chloroplast ATP Synthase γ Subunit Results in High Non-photochemical Fluorescence Quenching and Altered Nuclear Gene Expression in Arabidopsis thaliana

Bosco

Lezhneva

Biehl³

et al. 2004

102

The nuclear atpC1 gene encoding the ␥ subunit of the plastid ATP synthase has been inactivated by T-DNA insertion mutagenesis in Arabidopsis thaliana. In the seedling-lethal dpa1 (deficiency of plastid ATP synthase 1) mutant, the absence of detectable amounts of the ␥ subunit destabilizes the entire ATP synthase complex. The expression of a second gene copy, atpC2, is unaltered in dpa1 and is not sufficient to compensate for the lack of atpC1 expression. However, in vivo protein labeling analysis suggests that assembly of the ATP synthase ␣ and ␤ subunits into the thylakoid membrane still occurs in dpa1. As a consequence of the destabilized ATP synthase complex, photophosphorylation is abolished even under reducing conditions. Further effects of the mutation include an increased light sensitivity of the plant and an altered photosystem II activity. At low light intensity, chlorophyll fluorescence induction kinetics is close to those found in wild type, but non-photochemical quenching strongly increases with increasing actinic light intensity resulting in steady state fluorescence levels of about 60% of the minimal dark fluorescence. Most fluorescence quenching relaxed within 3 min after dark incubation. Spectroscopic and biochemical studies have shown that a high proton gradient is responsible for most quenching. Thylakoids of illuminated dpa1 plants were swollen due to an increased proton accumulation in the lumen. Expression profiling of 3292 nuclear genes encoding mainly chloroplast proteins demonstrates that most organelle functions are down-regulated. On the contrary, the mRNA expression of some photosynthesis genes is significantly up-regulated, probably to compensate for the defect in dpa1.

“…Some COX was also detected in the respiratorycompetent strain with longer exposure time of the blot ( Western analysis with an antibody against the ␤-subunit of F 1 failed to detect the 200 -400 kDa bands, indicating that they did not contain the F 1 -Atp9p ring assembly intermediate of the ATP synthase (1,38). Cox1p intermediates, some of which migrate in the 200 -400-kDa region of the blue native gel, are absent in mss51 mutants (5).…”

Section: Properties Of the Atp9p-cox6pmentioning

confidence: 99%

Assembly of the Rotor Component of Yeast Mitochondrial ATP Synthase Is Enhanced When Atp9p Is Supplied by Atp9p-Cox6p Complexes

McStay

Tzagoloff

2014

Background:The Atp9p rotor is an assembly module of mitochondrial ATP synthase. Results: Newly translated Atp9p and Cox6p, a subunit of yeast cytochrome oxidase (COX), are present in large complexes. Conclusion: Atp9p-Cox6p complexes serve as a source of Atp9p for rotor formation. Significance: We propose that Cox6p enhances the efficiency of Atp9p ring formation and may also coordinate balanced expression of COX and ATP synthase.