INFLUENCE OF THE UV-ACTIVATED SOS RESPONSE ON THE GAMMA-RADIATION-INDUCED MUTATION SPECTRUM IN THE LACI GENE

Previous studies of our group have shown that intracellular or extrace llular gamma-irradiation of the lad gene results in different mutation al spectra. One cause for these differences might be the error-prone S OS response, which is activated in the intracellular situation by gamm a-irradiation but not in the extracellular situation. Since UV-radiati on is a well-established strong inducer of the SOS response, we used b acterial host cells, pretreated with UV-light to study the influence o f the SOS response on the gamma-radiation-induced mutation spectrum in the lacI gene in the extracellular situation. If the SOS response was activated, mutations on A:T base pairs and frameshift mutations accou nted for 16% and 12% of all mutations, respectively, but they were har dly detected in the absence of an induced SOS response. G:C to T:A tra nsversions increased from 14% to 24% in the presence of an activated S OS response. We can therefore conclude from this study, that SOS-induc tion of host cells by UV-light influences the extracellular mutation s pectrum in the lad gene, with respect to mutations on A:T base pairs, G:C to T:A transversions and frameshift mutations. This conclusion is supported by the fact that the previously obtained intracellular gamma -radiation-induced mutation spectrum in the lad gene, in which the SOS response is also involved, shows great similarities with the extracel lular mutation spectrum in the presence of an activated SOS response i n this study. (C) 1998 Elsevier Science B.V. All rights reserved.