[Interference of inducible repair processes in Escherichia coli]

Radiation and the majority of chemical mutagens produce lesions in the DNA of cells which provoke the induction--as a reverse response--of some inducible repair processes. One of them is the adaptive response--highly specific in the repair of damages, induced by alkylating agents. This repair pathway decreases the toxic and mutagenic effects of many alkylating agents and can be induced in Escherichia coli cells exposed to sublethal concentrations of the same agents. By contrast, the SOS repair pathway in E. coli is non-specific and transient phenomenon which leads, among other things, to bacterial mutagenesis. It is controlled by the regulatory RecA protein which in its activated form promotes the cleavage of LexA repressor, allowing for the increased transcription of about 17 repressed genes--SOS regulon. The latter is not associated with the adaptive response. Nevertheless, there are experimental data indicating that the adaptive response is able to reduce some functions of the SOS repair activity--W-reactivation, W-mutagenesis and lambda phage induction. A relatively new bacterial short-term assay for genotoxicity, the SOS chromotest with E. coli PQ37 as an indicator organism, makes it possible to measure SOS induction indirectly, on the basis of a simple colorimetric assay. In the present study, the SOS chromotest in a completely automated system "Bioscreen C" was used to study interference between the adaptive and SOS responses in E. coli. Our data indicate that there is an inhibitory effect of the adaptive response on the SOS induction, as well as the negative interference between two successive SOS responses, at a transcriptional level of the SOS induction.