Double-strand Scissions in DNA of Gamma-irradiated Micrococcus radiodurans and their Repair during Postirradiation Incubation

Strand scissions in DNA of M, radiodurans after in vivo irradiation with ⁶⁰Co gamma rays were investigated by the sedimentation analysis using neutral sucrose gradients. Double-strand scission in DNA was estimated to occur at the rate of one double cut per 800 eV. This rate is in a good agreement of the value reported for mammalian cells. The rejoining of these double-strand scissions was observed during the repair process of the post-irradiation incubation and the mean rejoining time, i.e., the time reducing the remaining fraction of the double-strand scission to 0.37, was found to be 52 min. This rejoining repair was inhibited by adding chloramphenicol, tetracycline or actinomycin D to the postirradiation incubation medium. It is suggested that the high resistance character of M. radiodurans to gamma rays may be due to the efficient capacity of this rejoining repair.