Nitrous acid and alkylating nitrosamides: mutation fixation in Saccharomyces cerevisiae.

Abstract

The frequency of reverse mutants in two haploid, adenine requiring strains ofSaccharomyces cerevisiae induced with nitrous acid and alkylating nitrosamides is reduced by incubating cells after treatment at elevated temperature. Under these conditions survival is affected to a much weaker and rather variable extent. The temperature effect is independent of residual growth, and, therefore, most probably has no influenec on mutation expression. After treatment cells were plated and initially incubated at low temperature. At various intervals after plating cells were then transferred to elevated temperature. In other experiments the transfer was performed from an initial high to a final low temperature. This procedure led to the detection of a temperature sensitive phase which was reached only several hours after plating. Respreading experiments showed that the temperature sensitive phase was terminated a few hours before the number of mutant cells had doubled. It is argued that the temperature sensitive phase coincides with processes involved in the preparation of cell division, presumably DNA synthesis. Elevated temperature probably interferes with the process of mutation fixation which is assumed to consist of incorporation of altered DNA precursors or replication mistakes due to altered bases in the DNA strands.