Mucidin-resistant antimycin A-sensitive mitochondrial mutant of Saccharomyces cerevisiae

Random mutant generation and its utility in uncovering structural and functional features of cytochrome b in Saccharomyces cerevisiae

The generation of random mutations in the mitochondrial cytochrome b gene of Saccharomyces cerevisiae has been used as a most fruitful means of identifying subregions that play a key role in the bc1 complex mechanism, best explained by the protonmotive Q cycle originally proposed by Peter Mitchell. Selection for center i and center o inhibitor resistance mutants, in particular, has yielded much information. The combined approaches of genetics and structural predictions have led to a two-dimensional folding model for cytochrome b that is most compatible with current knowledge of the protonmotive Q cycle. A three-dimensional model is emerging from studies of distant reversions of deficient mutants. Finally, interactions between cytochrome b and the other subunits of the bc1 complex, such as the iron-sulfur protein, can be affected by a single amino acid change.

Isolation and RNA sequence analysis of cytochrome b mutants resistant to funiculosin, a center i inhibitor of the mitochondrial ubiquinol-cytochrome c reductase in Saccharomyces cerevisiae

Funiculosin is a well-known inhibitor of the mitochondrial respiratory chain, probably acting at the ubiquinone reducing site or center i of QH2-cytochrome c reductase. We report here the isolation, mapping and RNA sequence analysis of yeast apo-cytochrome b mutants resistant to this inhibitor. Funiculosin-resistance was found to be conferred, in 4 independent isolates, upon replacement of a leucine residue by phenylalanine in position 198 of the cytochrome b polypeptide chain.

Antifungal agents as tools in experimental mycology

Both natural and synthetic substances are conveniently used for studying metabolism, genetic aspects, morphogenesis of cell structures, life cycle and differentiation of fungi.

Spectral properties of cytochrome b-561 and cytochrome b-565 in mucidin-resistant mutants of Saccharomyces cerevisiae

The oxidation of NADH in submitochondrial particles isolated from MUC1, MUC2 and MUC3 mucidin-resistant mutants of Saccharomyces cerevisiae is specifically resistant to mucidin. Extra reduction of cytochrome b-565 induced by mucidin is demonstrated in all tested mucidin-resistant mutants. Red shift of cytochrome b-561 is induced by mucidin in two independent MUC3 mutants. In MUC1 and MUC2 mutants, the red shift is not induced by mucidin, while that promoted by antimycin A and 2-n-heptyl-4-hydroxyquinoline N-oxide are normal. It is concluded that the extra reduction of cytochrome b-565 and the red shift of cytochrome b-561 elicited by mucidin can be largely dissociated from the overall inhibition of the electron flow by distinct mucidin-resistant mutations in different exons of the split mitochondrial gene of cytochrome b.

Localization of mucidin-resistant locus muc3 on mitochondrial DNA with respect to ubiquinol-cytochrome c reductase deficient box loci. Locus muc3 is allelic to box2

Genetic relations between mitochondrial mucidin-resistant locus muc3 and ubiquinol-cytochrome c reductase-deficient box loci have been studied by recombination and petite deletion analysis. It was found that the locus muc3 maps in the segment of mitochondrial DNA corresponding to the locus box2. The results suggest the participation of box2/muc3 locus in the sequences of the structural gene for cytochrome b.

Mapping of the two mitochondrial antimycin A resistance loci in Saccharomyces cerevisiae

Retention or loss of the two new mitochondrial antimycin A resistance loci AI and AII has been analyzed in a large number of stable cytoplasmic petite mutants. Using these deletion mutants it was possible to localize the two antimycin A resistance loci in the OI--OII region of mitochondrial DNA. The genetic loci are mapped in the following order: OII--AI--AII--cobl--OI. The mapping relationship of mutants resistant to antimycin A or funiculosin to various cob mutants is described.

Mitochondrial heredity of resistance to 3-(3,4-dichlorophenyl)-1,1-dimethylurea, an inhibitor of cytochrome b oxidation, in Saccharomyces cerevisiae

3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), an inhibitor of cytochrome b oxidation, has been used for the selection of three resistant mutants (diur) of Saccharomyces cerevisiae. The mutant diur-64 exhibits in vivo cross-resistance to antimycin A while diur-34 and diur-1 are more sensitive to antimycin A than the parental strain. The three mutants exhibit mitochondrial inheritance according to the following criteria: mitotic segregation of diuron-resistant and diuron-sensitive diploids is obtained among the diploid progeny of a cross between diur and dius; non-Mendelian segregation of diuron resistance (4:0) is observed in spores of tetrads issued from diuron-resistant diploid; extensive ethidium bromide treatment leads to the formation of Q- mutants which no longer transmit diur and dius alleles. Evidence for two distinct diuron-resistant loci were obtained by allelism tests. Recombination analysis shows that diuron-resistance is not located in the polar region of the mitochondrial genome. The diur loci are not linked to the erythromycin locus since the upper limit in recombinants frequency (26%) for a non-polar region is obtained between diur and eryr. A low recombinants frequency (3%) is observed in crosses between diur-34 mutation and the two mutants cob1 and cob2 suggesting that diur-34 might be located between these two cytochrome-b-deficient loci. The resistance to diuron is also expressed in vitro since the oxidation rates of succinate by sonicated submitochondrial particles from the mutants are clearly less sensitive to diuron than that of the wild type.

Mucidin resistance in yeast. Isolation, characterization and genetic analysis of nuclear and mitochondrial mucidin-resistant mutants of Saccharomyces cerevisiae

Mutants of Saccharomyces cerevisiae resistant to the antibiotic mucidin, a specific inhibitor of electron transport between cytochrome b and c, were isolated and divided into three phenotypic groups, as follows. Class 1 mutants were cross-resistant to a variety of mitochondrial inhibitors and exhibited no resistance at the mitochondrial level. Class 2 mutants were specifically resistant to mucidin exhibiting resistance also at the level of isolated mitochondria. Biochemical studies indicated that the mucidin resistance in class 2 mutants involved a modification of mucidin binding of inhibitory sites on the mitochondrial inner membrane without a significance change in the sensitivity of mitochondrial oxygen uptake to antimycin A, 2-heptyl-4-hydroxyquinoline-N-oxide, and 2,3-dimercaptopropanol. Class 3 was represented by a mutant which showed a high degree of resistance to mucidin and was cross-resistant to a variety of mitochondrial inhibitors at the cellular level but exhibited only a resistance to mucidin at the mitochondrial level. Genetic analysis of mucidin-resistant mutants revealed the presence of both nuclear and mitochondrial genes determining mucidin resistance/sensitivity in yeast. Resistance to mucidin in class 1 mutants was due to a single-gene nuclear recessive mutation (mucPR) whereas that in class 2 mutants was caused by mutations of mitochondrial genes. Resistance in class 3 mutant was determined both by single-gene nuclear and mitochondrial mutations. In the mitochondrial mutants the mucidin resistance segregated mitotically and the resistance determinant was lost upon induction of petite mutation by ethidium bromide. Allelism tests indicated that the mucidin resistance mutations fell into two genetic loci (MUC1 and MUC2) which were apparently not closely linked in the mitochondrial genome. Recombination studies showed that the two mitochondrial mucidin loci were not allelic with other mitochondrial loci RIB1, RIB2 and OLI1. An extremely high mucidin resistance at the cellular level was shown to arise from synergistic interaction of the nuclear gene mucPR and the mitochondrial mucidin-resistance gene (MR) in a cell. The results suggest that at least two mitochondrial gene products, responsible for mucidin resistance/sensitivity in yeast, take part in the formation of the cytochrome bc1 region of the mitochondrial respiratory chain.

Cytoplasmic inheritance of antimycin A resistance in Saccharomyces cerevisiae

Three antimycin resistant mutants of Saccharomyces cerevisiae are characterized genetically. The mutations have been shown to be cytoplasmically inherited by four criteria. The phenotype persists in diploids formed by a cross with a pO strain of yeast of the opposite mating type. Diploids heterozygous for the antimycin marker, however, show segregation of the resistance and sensitivity during mitosis. Tetrad analysis indicates a non-Mendelian segregation (4:0 and 0:4) of the mutations. The antimycin marker can be eliminated by ethidium bromide treatment under conditions that should have deleted all of the mitochondrial DNA.