Induction and repair of strand breaks and 3'-hydroxy terminals in the DNA of mammalian cells in culture following gamma-ray irradiation.
DNA was isolated in a fairly pure and intact state from cultured mouse leukaemia cells (L5178Y) after gamma-ray irradiation using a hydroxyapatite column chromatography method, and analysed further by sucrose gradient centrifugation or DNA polymerase (EC 2.7.7.7, enzyme A of Klenow from Escherichia coli) assay. Irradiation of the cells induced single- and double-strand breaks in the DNA with an efficiency of 100 eV/break and 1300 eV/break, respecitvely. Approximately 50% of the single-strand breaks were estimated to be those arising from allali-labile lesions. A linear, dose-dependent increase was found in the template activity of the DNA, indicating the induction of 3'-OH terminals by gamma-irradiation. Post-irradiation incubation of the cells in serum-free medium allowed the majority of the breaks to rejoin within a few hours. Repair of the alkali-labile lesions was, however, found to be much slower than that of "actual" single-strand breaks. A slight increase of the DNA template activity was found during the period of post-irradiation incubation. The reason for the increase is discussed.
D000818:Animals; D002478:Cells, Cultured; D004260:DNA Repair; D004273:DNA, Neoplasm / Q000528:radiation effects*; D004259:DNA-Directed DNA Polymerase; D005720:Gamma Rays; D007942:Leukemia, Experimental; D007945:Leukemia, Lymphoid; D008970:Molecular Weight; D013698:Templates, Genetic
D004273:DNA, Neoplasm; D004259:DNA-Directed DNA Polymerase