[Escherichia coli K-12 mutants with enhanced resistance to ionizing radiation. II. Study of DNA damage and repair in gamma-irradiated cells].
Formation and repair of single-stranded breaks (ssb) and double-stranded breaks (dsb) in DNA of gamma-irradiated cells of three Escherichia coli strains (the parental strain AB1157 and radiation-resistant mutants Gamr444 and Gamr445) were studied by centrifugation in alkaline or neutral sucrose gradients. The initial yield of ssb and the kinetics of their repair during post-irradiation incubation in a growth medium are similar for Gamr mutants and the wild-type strain. The yield of dsb in the chromosome of Gamr mutants is significantly lower than in chromosomal DNA of the parental strain, both immediately after gamma-irradiation and after three hours of post-irradiation incubation in a growth medium. The decreased yield of dsb in the Gamr mutants correlates with their relative radioresistance. It was found also that the level of DNA degradation is significantly lower in UV- or gamma-irradiated cells of Gamr mutants, as compared with the wild-type strain. It is suggested that enhanced radioresistance of the Gamr mutants is due to decreased formation of enzymatically induced dsb, as a consequence of moderated DNA degradation under the action of repair exonucleases and also to enhanced efficiency of dsb repair.
D004260:DNA Repair / Q000528:radiation effects*; D004269:DNA, Bacterial / Q000235:genetics / Q000528:radiation effects*; D004277:DNA, Single-Stranded / Q000235:genetics / Q000528:radiation effects; D004926:Escherichia coli / Q000235:genetics / Q000528:radiation effects*; D005720:Gamma Rays; D009154:Mutation; D011836:Radiation Tolerance
D004269:DNA, Bacterial; D004277:DNA, Single-Stranded
Mutanty Escherichia coli K-12 s povyshennoĭ ustoĭchivost'iu k ioniziruiushcheĭ radiatsii. Soobshchenie II. Izuchenie povrezhdeniia i reparatsii DNK v gamma-obluchennykh kletkakh.