The mitochondrial targeting presequence of the Rieske iron-sulfur protein is processed in a single step after insertion into the cytochrome bc1 complex in mammals and retained as a subunit in the complex.
The amino acid sequence of subunit 9 of the bovine heart cytochrome bc1 complex is identical to the 78-amino acid presequence that is removed post-translationally from the Rieske iron-sulfur protein as it is imported and targeted to the mitochondrial cytochrome bc1 complex. Iron-sulfur protein precursor, generated by in vitro transcription and translation, is processed to mature size in a single step when incubated with rat liver mitochondria, and generates a peptide that comigrates on SDS-polyacrylamide gel electrophoresis with subunit 9. These results suggest that the Rieske protein is processed in a single proteolytic step after it is inserted into the cytochrome bc1 complex in mammals, and that the processed presequence remains as a subunit of the complex. This is apparently the first instance in which a cleaved targeting presequence has been shown to be retained in the cell, possibly exhibiting a second function in addition to its function in protein trafficking.
Brandt
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Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03755.
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Trumpower
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D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002417:Cattle; D004247:DNA; D014450:Electron Transport Complex III / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007506:Iron-Sulfur Proteins / Q000235:genetics / Q000378:metabolism*; D008929:Mitochondria, Heart / Q000378:metabolism*; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D017386:Sequence Homology, Amino Acid
D007506:Iron-Sulfur Proteins; D010446:Peptide Fragments; C037989:Rieske iron-sulfur protein; D004247:DNA; D014450:Electron Transport Complex III