EXPRESSION OF THE ESCHERICHIA-COLI ADA GENE IN YEAST PROTECTS AGAINST THE TOXIC AND MUTAGENIC EFFECTS OF N-METHYL-N'-NITRO-N-NITROSOGUANIDINE

The E.coli ada gene protein coding region has been ligated into an extrachromosomally replicating yeast expression vector downstream of the yeast alcohol dehydrogenase gene promoter region to produce pADHO6C. The yeast strains SX46A, 7799-4B and VV-6 are deficient in endogenous O6-alkylguanine-DNA-alkyltransferase and transformation of these strains with this shuttle vector resulted in the expression of 1730, 1260 and 374 fmoles ada-encoded ATase/mg protein in stationary phase yeast: transformation with the parent vector had no effect on endogenous ATase activity which remained less than 2 fm/mg. In comparison with parent vector transformed yeast, all of the pADHO6C-transformed strains showed an increase in the resistance to the toxic effects of N-methyl-N′-nitro-N-nitrosoguanidine (MNNG). In addition, 7799-48 and VV-6 were more resistant to the mutagenic effects of this agent. These results indicate that the toxic and mutagenic effects of MNNG in yeast are mediated, at least in part, by DNA lesions that can be repaired by the E.coli ada gene product. © 1990 Oxford University Press.