A yeast screening system for simultaneously monitoring multiple genetic endpoints

Mutation, recombination, and mitochondrial deficiencies have been proposed to have roles in the carcinogenic process. We describe a diploid strain of the yeast Saccharomyces cerevisiae capable of detecting this wide spectrum of genetic changes. Strain XD83 can detect forward mutation, back nuclear frameshift and base-pair substitution mutation, nuclear intragenic and intergenic recombination, and mitochondrial forward point mutations and deletions. The markers used for monitoring these events have been especially well characterized genetically. Ultraviolet light was chosen as a model carcinogenic agent to test this system. In addition to highly significant (P less than 0.01) increases in the frequencies of each genetic change, increases in the absolute numbers (yields) of each change indicated induction and not selective survival. The relative amounts of each type of genetic change varied with dose and should be considered a part of the spectrum of change induced by ultraviolet light. The wide spectrum of endpoints monitored in the XD83 yeast system may allow the detection of certain carcinogens and other genetically toxic agents which have escaped detection in more limited systems. Since only one strain is required to simultaneously monitor these genetic changes, this assay system should facilitate comparisons of the induced changes and be more efficient than using multiple strains to monitor the same endpoints.