Comparative Studies on the Effect of Ionizing and Nonionizing Radiations on the Kinetics of DNA Synthesis and Postirradiation Degradation in Micrococcus radiodurans R₁₁5 ¹⁾

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The kinetics of degradation and synthesis of DNA and the nature of radioactive substances released from M. radiodurans R₁₁5 labeled with thymidine-methyl-³H after UV and gamma irradiations were investigated. The release of labeled material from the DNA began immediately upon incubation and terminated in due time 90 min and 180 min for UV and gamma irradiations, respectively. When acriflavine was added to the medium, post-irradiation degradation process did not terminate even after 9 h in the case of UV exposure. However, it terminated after 6 h in the case of gamma irradiation. In the presence of acriflavine, DNA synthesis resumed after termination of DNA degradation in the case of gamma irradiation and this was not observed in the case of UV irradiation.
Degradation products were chromatographed and it was found that they were located in one major radioactive peak. However their locations were different for UV and gamma radiations. For UV irradiation, the peak fell in the thymine region, while for gamma irradiation it fell in the thymidine region.