Analysis of interactions between mutagens, I. Heat and ultraviolet light in Saccharomyces cerevisiae

A new mathematical approach to the description of interaction data (Ager and Haynes, 1987) is applied here to the interaction between heat and ultraviolet light (UV) in Saccharomyces cerevisiae. A strong synergism for cell killing is found to be associated with large increases in gene conversion (of up to 8-fold), and mutation (of up to 14-fold). Analysis of the interaction data for both wild-type and repair-deficient strains indicates that the heat-UV synergism arises via the inhibition of two different repair pathways. Unambiguous conclusions regarding the molecular mechanisms by which these repair processes are inhibited cannot be drawn on the basis of dose-response data alone. However, this approach does enable one to make well defined, empirical comparisons of the nature and kinetics of such interactions.