On the mechanism of petite genesis in yeast. IV. Biochemical characterization of a conditional cytoplasmic mutant producing petites at restrictive temperature

On the formation of rho- petites in yeast. II. Effects of mutation tsm-8 on mitochondrial functions and rho-factor stability in Saccharomyces cerevisiae

1. In non-fermentable substrates growth of mutant tsm-8 cells of Saccharomyces cerevisiae is restricted to about one generation after shift from 23 to 35 degrees C. Non-permissive conditions (35 degrees C, glycerol) cause a gradual decrease in respiration to about 20% of the activity at permissive temperature 23 degrees C). 2. Anaerobically grown and glucose-repressed mutant cells exhibit a decreased adaptation rate of mitochondrial functions to aerobic growth and non-fermentative growth, even at 23 degrees C, as revealed by determination of respiratory rates and mitochondrial protein synthesis. 3. At 35 degrees C, rho+ cells of mutant tsm-8 are converted to p- cells within 6-8 generations of growth, in all fermentable substrates tested. Drugs or antibiotics as nalidixic acid, acriflavin, chloramphenicol and erythromycin, bongkrecic acid, antimycin and FCCP, as well as anaerobiosis, have little or no influence on this kinetics. A heat shock does not yield rho- petites to a significant extent. 4. Reversion of tsm-8 cells to wild type function, which occurs spontaneously with a frequency of 10(-8), is found to be due to a mitochondrial mutational event.

Macromolecular synthesis and energy level in a mitochondrial conditional yeast mutant, tsm-8

Mitochondrial DNA, protein and ATP syntheses persist at non-permissive temperature (35 degrees C) in the mitochondrial, conditionally rho- petites forming yeast mutant, tsm8. Protein and ATP syntheses, however, are diminished during prolonged incubation at 35 degrees C in non-fermentable substrate. Mitochondrial RNA synthesis decreases rapidly to a residual constant level of about 10% of the initial value after the shift to 35 degrees C. The decrease is reversed by returning to permissive conditions. Evidence is presented that this temperature-induced decrease in mitochondrial transcription rate is effected by a mutationally altered regulatory process rather than by temperature sensitivity of mitochondrial RNA polymerase. It is concluded that rho- petite formation in mutant tsm8 is not effected by complete inhibition of macromolecular and ATP syntheses but is correlated with a reduction in mitochondrial transcription.

Mapping of mutation tsm-8 with respect to transfer RNA genes on the mitochondrial DNA of Saccharomyces cerevisiae

A precise localization of the tsm-8 mutation in relation to the transfer RNA genes has been attempted by rho- deletion analysis. The data show that the tsm-8 mutation is in close proximity to the isoleucyl transfer RNA gene. However, it is not yet possible to decide whether the tsm-8 mutation is within this transfer RNA gene.

On the formation of rho- petites in yeast. I. Multifactorial mitochondrial crosses (rho+ X rho+) involving a mutation conferring temperature-sensitivity of rho factor stability

The inheritance of an extrakaryotic mutation conferring temperature-sensitive growth on non-fermentable substrates and a high frequency of mutation to rho- has been studied. Multifactorial crosses (rho+ X rho+) involving this mutation TS8 and mitochondrial mutations conferring resistance to chloramphenicol, erythromycin, oligomycin or paromomycin revealed: a) Mutation TS8 is localized on the mitDNA, referring to a new gene locus TSM1. b) Locus TSM1 appears to be weakly linked to the locus PAR1 and to the loci RIB1 and RIB3 but unlinked to the locus OLI1. c) The position of TSM1 is between PAR1 and the two closely linked loci RIB1 and RIB3, OLI1 is outside and not linked to the segment PAR-TSM-RIB. d) Mutation TS8 does not significantly influence the process of mitochondrial recombination and its control by the mitochondrial locus omega.