title: Double-strand breaks from single photochemical events in DNA containing 5-bromouracil.
abstract: Ultraviolet irradiation of Escherichia coli cells with a low level of 5-bromouracil incorporated produces DNA double-strand breaks by single photochemical events, one such break per 100 single-strand breaks, the latter assayed in alkali-denatured DNA. About 2.5--4 double-strand breaks are produced per "lethal hit," compared with about 6 double-strand breaks per lethal hit induced by gamma rays. These results are consistent with the hypothesis that an unrepaired DNA double-strand break is a major lethal event in both cases. The increase in sensitivity to ultraviolet (measured by colony-forming ability) seems linear in the number of bromouracils incorporated (0--20% of the thymines), and the linear relationship is much the same for incorporation in one or in both strands of the DNA double helix.
mesh_terms: D001976:Bromouracil / Q000378:metabolism / Q000494:pharmacology*; D002499:Centrifugation, Density Gradient; D003114:Colony-Forming Units Assay; D004269:DNA, Bacterial / Q000528:radiation effects*; D004277:DNA, Single-Stranded / Q000528:radiation effects; D004926:Escherichia coli / Q000378:metabolism / Q000528:radiation effects; D009691:Nucleic Acid Denaturation; D010777:Photochemistry; D014466:Ultraviolet Rays
chemical_list: D004269:DNA, Bacterial; D004277:DNA, Single-Stranded; D001976:Bromouracil