Sue1p is required for degradation of labile forms of altered cytochromes c in yeast mitochondria

Abstract

Previous studies on certain altered holo-isocytochromes c revealed a ρ--dependent degradation (RDD) phenotype, in which certain altered holo-iso-1-cytochromes c are at normal or nearly normal levels in ρ+ strains, but are at low levels or absent in ρ- strains, although wild-type holo-iso-1-cytochrome c is present at normal levels in both ρ+ and related ρ- strains. The diminished levels of altered holo-iso-1-cytochrome c are due to the rapid degradation that is carried out by a novel proteolytic pathway in the IMS of mitochondria. SUE1, a nuclear gene that encodes a mitochondrial protein, was identified with a genetic screen for mutants that diminish RDD. The levels of RDD and certain other types of altered holo-iso-1-cytochrome c were elevated in ρ- sue1 strains. Also, ρ+ sue1 strains containing certain altered holo-iso-1-cytochromes c grew better on non-fermentable carbon sources than the corresponding ρ+ SUE1 strains. These results indicate that Sue1p may play an important role in the degradation of abnormal holo-iso-1-cytochrome c in the mitochondria.