Harman and norharman induce SOS responses and frameshift mutations in bacteria

Norharman and harman, beta-carboline derivatives with comutagenic activity in Salmonella typhimurium, were examined for their activity to induce SOS responses in S. typhimurium using the umu-test and mutations in Escherichia coli. The inducibility of the umuC gene by norharman and harman was assayed by measuring the levels of beta-galactosidase activity in tester cells harbouring the umuC'-'lacZ fusion gene on a plasmid. In the umu-test, both norharman and harman weakly induced umuC gene expression at 25-100 and 50-150 micrograms/ml, respectively. In the mutation test using reversion from trpE9777 to Trp+, harman was relatively more potent than norharman in inducing the mutations. These results indicate that norharman and harman induce SOS responses as well as reversion of trpE9777 frameshift mutation in bacteria.