Identification of a mitochondrial endonuclease involved in mt-DNA repair of Saccharomyces cerevisiae.

The activity of a yeast mitochondrial endonuclease extracted from mutants (sas1) with increased sensitivity to petite-inducing treatments was compared to that from wild-type cells. The specificity of the endonuclease was altered in haploids carrying a single mutant nuclear gene that conferred increased sensitivity to petite induction by ultraviolet light, by growth at an elevated temperature and by growth in the presence of aminopterin and sulfanilamide. At high ionic strengths the endonuclease from the mutants digested double stranded DNA much faster than did that from the wild-type strain.

Some properties of a mitochondrial endonuclease from yeast.

A mitochondrial endonuclease from Saccharomyces cerevisiae was previously shown to cut both strands of native DNA at opposite or nearby sites. The present studied demonstrate that the endonuclease activity is dependent on the strength of the hydrogen bonds between the DNA strands; the activity was measured at different ionic strengths, with substrates of different base compositions and also with DNA in which the double helix has been locally destabilized by ultraviolet irradiation, by depurination, and by single-stranded nicks. The activity is 30% greater with mitochondrial DNA (mt-DNA) than with nuclear DNA.

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.

An endonuclease from yeast mitochondrial fractions.

A membrane-bound endonuclease has been isolated from mitochondrial fractions of Saccharomyces cerevisiae. The enzyme is present in a stable complex and has an approximate molecular weight of 14 000. It requires Mg2+ or Mn2+ for activity, and has an optimum pH of 7.

Alterations in mitochondrial DNA of yeast which accompany genetically and environmentally controlled changes in rho- mutability.

Alterations in the physical characteristics of mitochondrial DNA accompanied increased spontaneous mutability to cytoplasmic respiratory-deficiency in yeast. Two systems were used to modify mutation rates, one physiological, the other genetic. Cells in log phase were shown to be more mutable than cells in stationary phase, and glucose-repressed cells were shown to be more mutable than unrepressed cells.