Sensitivity to methylmethanesulfonate and nitrous acid of ultraviolet light-sensitive mutants in Saccharomyces cerevisiae

Summary Twenty two ultraviolet light-sensitive mutants isolated byParry andCox (1968) were tested for a possible cross-sensitivity to nitrous acid and methylmethanesulfonate. Eighteen of these mutants showed, in comparison to wild type, an increased sensitivity to methylmethanesulfonate and 16 mutants were cross-sensitive to nitrous acid. Cross-sensitivity between these two chemicals was good even when the degrees of sensitivity were compared; only two major exceptions were found. The degree of sensitivity to the two chemicals on one side and to ultraviolet light was not always the same. Two mutants of extreme sensitivity to chemicals were only weakly sensitive to ultraviolet light whereas in another mutant an extreme sensitivity to ultraviolet light was combined with a low sensitivity to chemicals. These observations are discussed in the light of current views on excision repair models.