Effect of irradiation and mutagenic chemicals on the generation of ADH2- and ADH4-constitutive mutants in yeast: the inducibility of Ty transposition by UV and ethyl methanesulfonate.

A strain defective in fermentation due to a deletion in the ADH1 gene was used to generate revertants which are constitutive mutants of the genes ADH2 and ADH4. By analyzing the DNA of the mutants we determined the frequency of Ty insertions into the promoter region of these genes. We found an increase in transposition after UV irradiation and treatment with ethyl methanesulfonate (EMS). Chemical inhibition of DNA synthesis and translation decreased the induced mutant yield and the transposition frequency, whereas inhibition of transcription had no effect. Differences in transposition frequencies between different strains and between the 2 loci lead to the conclusion that not only the transposable element itself but also the insertion sites determine the frequency of Ty transposition to a given locus.