title: Cloning and characterization of a yeast cytochrome b5-encoding gene which suppresses ketoconazole hypersensitivity in a NADPH-P-450 reductase-deficient strain.
abstract: Cytochrome P-450 (Cyp) 51 or lanosterol-C14-demethylase is the main target for antifungal compounds of the triazole family like ketoconazole (Kz). Disruption of the associated NADPH-P-450 reductase-encoding gene (YRED) is not lethal, but decreases by about 20-fold the Kz resistance (KzR) of wild-type (wt) Saccharomyces cerevisiae. Transformation of a YRED-disrupted strain by a yeast genomic library based on a multicopy vector allowed us to identify a suppressor of Kz hypersensitivity. Deletion analysis of the 5-kb cloned fragment indicated that yeast cytochrome b5-encoding gene (CYB5), which encodes a 120-amino-acid (aa) protein, is required and sufficient for the suppressor effect. The encoded polypeptide shares about 30% aa identity with mammalian cytochromes b5 (Cyb5). CYB5 disruption and tetrad analysis demonstrate that yeast Cyb5 is not required for growth in a Yred+ strain. Determination of the microsomal content of b-type cytochromes by differential spectra indicated the presence of a strongly decreased or null Cyb5 level in the disrupted strain. This confirms that we have cloned the gene encoding the major microsomal form of Cyb5 which appears not to be essential. Minor Cyb5 isoforms could also be present in yeast or other redox proteins could substitute for the pleiotropic roles of Cyb5 in the sterol and lipid biosynthesis pathways.
authors.affiliation: Centre de Génétique Moléculaire du Centre National de la Recherche Scientifique, Gif-sur-Yvette, France.
authors.forename: G
authors.initials: G
authors.lastname: Truan
authors.forename: J C
authors.initials: JC
authors.lastname: Epinat
authors.forename: C
authors.initials: C
authors.lastname: Rougeulle
authors.forename: C
authors.initials: C
authors.lastname: Cullin
authors.forename: D
authors.initials: D
authors.lastname: Pompon
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D015786:Cytochromes b5 / Q000235:genetics*; D004271:DNA, Fungal; D004352:Drug Resistance, Microbial / Q000235:genetics; D007654:Ketoconazole / Q000494:pharmacology*; D008969:Molecular Sequence Data; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism*; D016366:Open Reading Frames; D010641:Phenotype; D015183:Restriction Mapping; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000201:enzymology / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D014170:Transformation, Genetic
chemical_list: D004271:DNA, Fungal; D015786:Cytochromes b5; D009251:NADPH-Ferrihemoprotein Reductase; D007654:Ketoconazole