Inactivation of the Gene Encoding the 11-kDa Subunit VIII of the Ubiquinol-cytochrome-c Oxidoreductase in Saccharomyces Cerevisiae

The single nuclear gene encoding the 11-kDa subunit VIII of the ubiquinol-cytochrome-c oxidoreductase (complex III) in Saccharomyces cerevisiae has been inactivated by a one-step gene disruption procedure. Inactivation results in a loss of ubiquinol-cytochrome-c oxidoreductase activity (less than 1% wild type) and respiratory deficiency. Cells lacking the 11-kDa protein also display lowered steady-state levels of other complex-III subunits encoded by nuclear genes including the 14-kDa subunit VII and the Rieske Fe-S protein and of the mitochondrially encoded cytochrome b. The steady-state levels of the transcripts from the genes encoding these proteins are however not reduced. The results strongly imply that the 11-kDa protein plays an important role in regulating the synthesis of complex III at the post-transcriptional level, most likely assembly. Separation of chromosomes by pulsed-field gel electrophoresis of DNA of wild-type and of the mutant lacking the 11-kDa-protein gene followed by Southern blot analysis reveals that the latter gene is located on chromosome X rather than on XII as reported by Van Loon et al. [Mol. Gen. Genet. 197 (1984) 219-224].