Isolation of Suppressive Sensitive Mutants from Killer and Neutral Strains of SACCHAROMYCES CEREVISIAE.

Dominant sensitive mutants were isolated from a killer and a neutral strain of Saccharomyces cerevisiae by treatment with nitrosomethylurethane. Genetic studies suggest that these sensitives arose by mutation of the wild-type cytoplasmic genetic determinants (k) or (n) to a mutant form (s). (s) determinants lack wild-type (k) and (n) activity but are retained in the cell and suppress the replication or activity of the wild-type determinants, converting killer and neutral cells to the sensitive phenotype. These mutants show an obvious similarity in behavior to suppressive petite mutants of yeast.