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The C‐terminal domain of yeast cytochrome b is essential for a correct assembly of the mitochondrial cytochrome bc 1 complex
Author(s) -
di Rago Jean-Paul,
Macadre Catherine,
Lazowska Jaga,
Slonimski Piotr P.
Publication year - 1993
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(93)80984-3
Subject(s) - frameshift mutation , mutant , biology , cytochrome , biochemistry , cytochrome b , nonsense mutation , stop codon , cytochrome c , heme , amino acid , cytochrome c1 , wild type , peptide sequence , c terminus , mutation , coenzyme q – cytochrome c reductase , mitochondrion , gene , mitochondrial dna , enzyme , missense mutation
Yeast mutants modifying the C‐terminal region of mitochondrial cytochrome b were isolated and characterized. A nonsense mutation of the leucine codon 335 (TTA → TAA), 50 residues before the normal C‐terminus, blocks incorporation of heme into the apocytochrome b and prevents growth on non‐fermentable substrates. The same defects were observed in a frameshift mutant (after codon 348, TAT → TATT) in which the last 37 C‐terminal residues are predicted to be replaced by a novel sequence of 33 amino acids. Function was regained in the nonsense mutant only by true back mutations restoring a protein of the wild‐type sequence. The respiratory capacity was restored to wild‐type levels in the frameshift mutant by a variety of single base subtractions located within a window of 24 bases before or after the original +T addition, these pseudo‐reversions resulted in single or multiple (up to five) consecutive amino acid replacements between positions 346 and 354 and restored the wild‐type sequence from position 355 to 385. These data, combined with hydropathy calculations and sequence comparisons, suggest that the C‐terminal domain of cytochrome b forms a transmembrane segment essential for the correct assembly of the cytochrome bc 1 complex.