ABSTRACT
The kinetics of the SOS induction in E. coli cells of wild type and deficient in umuC gene exposed to UV and gamma-rays were analysed. In the presence of UmuC protein SOS induction was 3-5.5 times lower and delayed for about 30 minutes after both UV and gamma rays. It was shown that decrease of the SOS induction in wild type cells irradiated by UV was due to more effective elimination of the photolesions from DNA by excision repair system. UmuCD-dependent inhibition of DNA replication was discussed as a possible mechanism allowing additional time for error-free repair.
Subject(s)
Bacterial Proteins/genetics , Escherichia coli Proteins , Escherichia coli/radiation effects , Genes, Bacterial/radiation effects , SOS Response, Genetics/radiation effects , Ultraviolet Rays , DNA, Bacterial/genetics , DNA-Directed DNA Polymerase , Escherichia coli/genetics , Gamma Rays , Gene Expression Regulation, Bacterial/genetics , Gene Expression Regulation, Bacterial/radiation effects , Genes, Bacterial/genetics , Luciferases/genetics , Mutation , Operon/genetics , Plasmids/genetics , Plasmids/radiation effects , SOS Response, Genetics/geneticsABSTRACT
The kinetic and dose dependencies of the SOS-induction in E. coli (uvrA) cells exposed to UV light were investigated. Below 2 J/m2 the rate of the SOS-induction increased with dose. The maximal level of the SOS-response was proportional to the UV dose. Pyrimidine dimers were necessary for the induction. In the dose range 2-10 J/m2 the rate of the SOS-induction decreased with dose. The dose-response curve was non-linear. Pyrimidine dimers were not required for the induction. The nature of the molecular events leading to the SOS-induction at low and high doses was discussed.
