Influence of methionine on the mutation frequency in Salmonella typhimurium.

When reversion of some markers in S. typhimurium was tested, it was found that addition of methionine to test plates increased the revertant yields. Two assumptions were made: (1) the effect of methionine reflects the necessity of intensive synthesis of some protein(s) required for abolishing the deleterious effects and/or expressing the mutagenic effects induced by mutagens; (2) methionine influences the mutagenesis via the DNA methylation process.