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.