Antimutagenic effects of chemicals on mutagenesis resulting from excision of a transposon in Salmonella typhimurium.

We have found that a temperature-sensitive mutation in the polA gene of Salmonella typhimurium strain LT2 causes precise excision of transposon Tn10 to occur at significantly increased frequencies in cells incubated at the restrictive temperature. In our experiments, precise excision from a site in the tryptophan operon was measured by determining the frequency of reversion of the auxotrophic trp1014::Tn10 polA7 strain to prototrophy on defined medium containing a trace amount of broth. Because the yields of revertants at 37 degrees C were of the order of 200 colonies per plate, it was possible to measure the effects of chemical inhibitors on the processes involved in precise excision. We now report that all of the DNA-repair inhibitors we have studied (caffeine, ethionine, acriflavine, procaine and cinnamaldehyde) are effective inhibitors of precise excision of Tn10, and can therefore be defined as antimutagens.