CHARACTERIZATION OF THE SACCHAROMYCES-CEREVISIAE NUCLEAR GENE CYB3 ENCODING A CYTOCHROME-B POLYPEPTIDE OF RESPIRATORY COMPLEX-II

Computer-assisted structural analysis of the predicted product of the previously described open reading frame (ORF) YKL4 located on the left arm of chromosome XI of Saccharomyces cerevisiae revealed a high degree of similarity (> 50%) to bovine cytochrome b560, the sdhC polypeptide of the Escherichia coli succinate dehydrogenase (SDH) complex and the protein specified by ORF137 located on the chloroplast DNA of Marchantia polymorpha. Disruption of the yeast gene severely impaired mitochondrial function, while Northern analysis showed it to be subject to catabolite repression. Deletion analysis of the CYB3 promoter identified a single HAP2/3/4-binding element that is necessary and sufficient for carbon source-dependent transcriptional regulation. These experiments also suggested the presence of additional, as yet unidentified, transcriptional control elements, both negative and positive. Taken together, these data lead us to conclude that the C YB 3 gene encodes the yeast homolog of the bovine cytochrome b560 component of complex II of the mitochondrial electron transport chain.