Occurence of an adaptive response of saccharomyces cerevisiae to chronic treatment with mutagens which is due to a dominant mutation

Organisms possess several pathways which counteract the effects of mutagens. One pathway is the adaptive response. Characteristic for this type of resistance is that it is induced within a few hours and that it is restricted to the repair of specific DNA-damage caused by alkylating agents. According to Maga and McEntee (MGG 200, 313-321, 1985), yeast cells lack the adaptive response. In long-term experiments for up to 400 days S.cerevisiae MP1 adapted to treatment with low doses of mutagens. Consistent results were obtained for the alkylating agent TRIETHYLENEMELAMINE as well as for the nonalkylating agent 4-NITROQUINOLINE 1-OXIDE. Furthermore, the adaptive response to the alkylating agent also adapted cells to the nonalkylating agent, which implies that there may be a single pathway for mutagens with different modes of action. Random spore analysis of adapted cells indicates that a dominant mutation is responsible for the resistance to low doses of mutagens. This resistance is reminis cent of multi-drug resistance in cultured mammalian cells rather than of the adaptive response in bacteria. (ITA)