Frameshift lesions induced by oxazolopyridocarbazoles are recognized by the mismatch repair system in Escherichia coli

The simple reversible intercalating agent isopropyl-OPC (iPr-OPC) induces frameshift-1 mutations in Salmonella typhimurium and Escherichia coli. The mutagenic responses of S. typhimurium and E. coli wild-type strains are not proportional to the amount of drug intercalated into double-stranded nucleic acids in living bacteria; it occurs only above a minimum level of binding. The fact that mismatch-repair-deficient (mutS) as well as adenine-methylation-deficient (dam) E. coli mutants are hypermutable at low concentrations of iPr-OPC suggests that the majority of mutants induced by this intercalating drug occur as mismatch-repairable mutations (or lesions) in the newly synthesized DNA strand close to the replication fork.