Temperature-sensitive mutations of Saccharomyces cerevisiae with defects in mitochondrial function

Level of ATP synthase activity required for yeast Saccharomyces cerevisiae to grow on glycerol media

Two independent cold-sensitive pet mutants in the gene (ATP5) coding for the oligomycin sensitivity conferring protein (OSCP) have been isolated in the yeast Saccharomyces cerevisiae. The mutations in both strains alter the initiating methionine codon in the ATP5 gene: ATG to ATA (Ile) and AAG (Lys). Western blot analysis of total yeast protein after the cells were grown at 18 degrees C, 30 degrees C, and 37 degrees C, indicates that the level of OSCP decreased 80% relative to the wild type strain. In addition, the level of the oligomycin-sensitive ATPase decreased 85% relative to the wild type strain, after growth at 30 degrees C. These findings indicate that for S. cerevisiae, the level of oxidative phosphorylation can decrease 85% without showing a large growth defect on media containing glycerol at 30 degrees C, but not at 18 degrees C.

Temperature sensitive pet mutants in yeast Saccharomyces cerevisiae that lose mitochondrial RNA

This is a description of a new class of temperature sensitive pet mutants in Saccharomyces cereviase that lose all or part of their mitochondrial RNA at the restrictive temperature. These mutants fall into 8 different complementation groups, mna1 to mna8, and 2 different classes based on their phenotype. Class I mutations, mna1-1 through mna5-1, cause complete or partial loss of mitochondrial RNA at the restrictive temperature. The mutation, mna1-1, is especially interesting since it causes a loss of both mitochondrial DNA and RNA when the mutant is grown on a fermentable carbon source at the restrictive temperature. However, when this mutant is grown at the permissive temperature on a non-fermentable carbon source then shifted to the restrictive temperature, only the mitochondrial RNA is lost. This indicates that the primary cause for the pet phenotype is due to the loss of mitochondrial RNA and not DNA. Class II mutations, mna6-1 through mna8-1, cause complete loss of the 14S rRNA after growth at the restrictive temperature in a fermentable carbon source. This loss appears to be specific for the 14S rRNA, since all other transcripts probed by Northern analysis are normal.

Nuclear mutations in Saccharomyces cerevisiae conferring multiple sensitivity to petite-inducing treatments

Eighteen EMS-induced mutant strains of S. cerevisiae with increased sensitivity to petite induction by sulfanilamide-aminopterin treatment have been isolated. Four of these strains demonstrated a concomitant increase in sensitivity to the petite-inducing effects of u.v. irradiation and of growth at an elevated temperature. Of these, two were shown to be a consequence of recessive nuclear mutations at one gene (sas1-1 and sas1-2). Expression of the two remaining mutations was too low to permit genetic analysis. All three petite-inducing treatments used in this study are known to reduce the hydrogen bond strength between the two strands of double stranded DNA, and the existence of multiple sensitivity is discussed in terms of an alteration of a mitochondrial endonuclease which acts preferentially at sites of reduced attraction.