Mutations in the membrane anchor of yeast cytochrome c1 compensate for the absence of Oxa1p and generate carbonate-extractable forms of cytochrome c1.
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.
Hamel
P
P
Centre de Génétique Moléculaire du Centre National de la Recherche Scientifique, 91198 Gif-sur-Yvette Cedex, France.
Lemaire
C
C
Bonnefoy
N
N
Brivet-Chevillotte
P
P
Dujardin
G
G
D000251:Adenosine Triphosphatases / Q000096:biosynthesis; D000595:Amino Acid Sequence; D002254:Carbonates; D002462:Cell Membrane / Q000201:enzymology; D003001:Cloning, Molecular; D003575:Cytochromes c1 / Q000096:biosynthesis / Q000235:genetics*; D004252:DNA Mutational Analysis; D004579:Electron Transport; D042963:Electron Transport Complex II; D014450:Electron Transport Complex III / Q000378:metabolism; D003576:Electron Transport Complex IV; D005800:Genes, Fungal / Q000235:genetics; D024101:Mitochondrial Proteins; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000378:metabolism; D009687:Nuclear Proteins / Q000502:physiology*; D009997:Osmotic Pressure; D010088:Oxidoreductases / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D013385:Succinate Dehydrogenase / Q000378:metabolism; D013489:Suppression, Genetic
D002254:Carbonates; D024101:Mitochondrial Proteins; D009097:Multienzyme Complexes; D009687:Nuclear Proteins; C090858:OXA1 protein; D003575:Cytochromes c1; D010088:Oxidoreductases; D042963:Electron Transport Complex II; D013385:Succinate Dehydrogenase; D003576:Electron Transport Complex IV; D000251:Adenosine Triphosphatases; D014450:Electron Transport Complex III