The iron-sulfur protein is necessary for the complete assembly of the low-molecular-weight subunits into the cytochrome b-c1 complex of yeast mitochondria.
A strain of yeast lacking the gene for the Rieske iron-sulfur protein (RIP) of the cytochrome b-c1 complex was used to study the assembly of this complex in the mitochondrial membrane. This strain lacks the mRNA for the iron-sulfur protein as evidenced by both Northern hybridization using a probe containing the coding region of the gene plus in vitro translation of total RNA followed by immunoprecipitation with a specific antibody against the iron-sulfur protein. In addition, isolated mitochondria from this strain lacked cytochrome c reductase activity with either succinate or the decyl analog of ubiquinol as substrate. Immunoblotting studies with antiserum against the cytochrome b-c1 complex revealed that mitochondria from the iron-sulfur protein-deficient strain have levels of core protein I, core protein II, and cytochrome c1 equal to those of wild-type mitochondria; however, a decrease in cytochrome b was evident from both immunoblotting and spectral analysis. Moreover, it is evident from the immunoprecipitates of radiolabeled mitochondria that the amounts of the low-molecular-weight subunits (17, 14, and 11 kDa) are decreased 53, 65, and 50%, respectively, in mitochondria lacking the iron-sulfur protein. These results suggest that the iron-sulfur protein is required for the complete assembly of the low-molecular-weight subunits into the cytochrome b-c1 complex.
Japa
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Department of Biochemistry, West Virginia University School of Medicine, Morgantown 26506.
Beattie
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DS
D015152:Blotting, Northern; D003573:Cytochrome b Group / Q000502:physiology*; D003574:Cytochrome c Group / Q000031:analogs & derivatives*; D003575:Cytochromes c1 / Q000502:physiology*; D007425:Intracellular Membranes / Q000648:ultrastructure; D007506:Iron-Sulfur Proteins / Q000502:physiology*; D008667:Metalloproteins / Q000502:physiology*; D008928:Mitochondria / Q000648:ultrastructure*; D011233:Precipitin Tests; D012441:Saccharomyces cerevisiae; D013057:Spectrum Analysis
D003573:Cytochrome b Group; D003574:Cytochrome c Group; D007506:Iron-Sulfur Proteins; D008667:Metalloproteins; D003575:Cytochromes c1