Enzymatic Induction of DNA Double-Strand Breaks in γ -irradiated Escherichia coli K-12

• Published in: Proceedings of the National Academy of Sciences - PNAS 1975-11, Vol.72 (11), p.4265-4269
• Main Authors: Bonura, Thomas, Smith, Kendric C., Kaplan, Henry S.
• Format: Article
• Language: English
• Subjects: Biochemistry; Cell Survival - radiation effects; DNA damage; DNA Nucleotidyltransferases - deficiency; DNA Repair; DNA, Bacterial - radiation effects; Dose-Response Relationship, Radiation; Escherichia coli; Escherichia coli - enzymology; Gamma Rays; Irradiation; Lesions; Models, Biological; Molecular weight; Mutation; Radiation damage; Radiation Effects; Sodium; Suspended solids; Temperature
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.72.11.4265

The polA1 mutation increases the sensitivity of E. coli K-12 to killing by γ -irradiation in air by a factor of 2.9 and increases the yield of DNA double-strand breaks by a factor of 2.5. These additional DNA double-strand breaks appear to be due to the action of nucleases in the polA1 strain rather than to the rejoining of radiation-induced double-strand breaks in the pol+strain. This conclusion is based upon the observation that γ -irradiation at 3 degrees did not affect the yield of DNA double-strand breaks in the pol+strain, but decreased the yield in the polA1 strain by a factor of 2.2. Irradiation of the polA1 strain at 3 degrees followed by incubation at 3 degrees for 20 min before plating resulted in approximately a 1.5-fold increase in the D0. The yield of DNA double-strand breaks was reduced by a factor of 1.5. The pol+strain, however, did not show the protective effect of the low temperature incubation upon either survival or DNA double-strand breakage. We suggest that the increased yield of DNA double-strand breaks in the polA1 strain may be the result of the unsuccessful excision repair of ionizing radiation-induced DNA base damage.