[Complementation between respiratory deficient mutants of Saccharomyces cerevisiae: establishment and regulation of respiration in the zygotes and their near descendants]

Genetic effects of formaldehyde in yeast. III. Nuclear and cytoplasmic mutagenic effects

Low concentrations of formaldehyde induce nuclear mutations when yeast cells are allowed to grow in the presence of this compound. The induction of reversions is a linear function of the concentration and depends upon the repair capacities of the treated cells. A strain defective in excision-repair (rad3-12) is more mutable by formaldehyde than the isogenic wild-type whereas a strain blocked in the mutagenic pathway (rad6-1) is not mutable after the same treatment. Allele specificities were found. In particular the lys1-1 mutation is not reversible by formaldehyde. Higher concentrations of formaldehyde induce efficiently the cytoplasmic "petite" mutation in non-growing conditions when a lethal effect is noticeable. The growth phase as well as the physiological state influence this mutagenic effect. The mutagenic effect of formaldehyde in yeast is discussed in relation with the repair processes involved.

Yeast mutants resistant to basic fuchsin: a genetic approach to the integration of nuclear and mitochondrial information

In yeast, basic fuchsin both inhibits mitochondrial functions and is a potent mutagen for the mitochondrial genome. A genetic analysis of two mutants resistant to the dye indicate that: (1) resistance is specified by a nuclear gene; (2) the onset of resistance in sensitive cells is controlled by the mitochondrial genome; and (3) sensitive mitochondrial structures can be carried over for many cell generations in the presence of a resistant nuclear genotype.

The respiratory chain in a ubiquinone-deficient mutant of Saccharomyces cerevisiae

1. Two allelic mutants of Saccharomyces cerevisiae with a deficiency in the biosynthesis of ubiquinone have been isolated. The properties of one particular mutant strain were investigated. Submitochondrial particles of this strain contain maximally 3% of the amount of ubiquinone in wild-type particles; the amounts of other components of the respiratory chain are essentially normal. 2. The respiratory rates of mutant cells, mitochondria and submitochondrial particles are low with ubiquinone-dependent substrates, but are restored to normal levels by addition of Q-1; the restored respiration is antimycin sensitive. Intact cells and mitochondria show respiratory control both in the absence and presence of Q-1. 3. The NADH:Q-1 oxidoreductase of submitochondrial particles of the mutant followspseudo first-order kinetics in [Q-1]. QH2-1 inhibits competitively with respect to Q-1, the Ki for QH2-1 being equal to the Km for Q-1. 4. Succinate dehydrogenase in both wild-type and mutant submitochondrial particles can be activated by NADH. 5. The turnover number of succinate dehydrogenase in the mutant, measured with phenazine methosulphate as primary electron acceptor, is about one-half that of wild-type particles. The turnover numbers measured with Q-1 as electron acceptor are about the same in the two types of particles. 6. The kinetics of redox changes in cytochrome b, in the presence of antimycin and oxygen, are distinctly different in the mutant and wild-type particles. They indicate that ubiquinone plays an important role in the phenomenon of the increased reducibility of cytochrome b induced by antimycin plus oxygen.