Sensitization ofEscherichia ColiC to Gamma-radiation by 5-bromouracil Incorporation

Abstract

Escherichia coli C cells, unifilarly substituted with 5-bromouracil (BrUra) were 2·25 times as sensitive as unsubstituted cells to killing by γ-irradiation under aerobic conditions. The yield of DNA double-strand breaks in BrUra-substituted cells was increased by a factor only 1·55, suggesting that other lesions also contribute to cell-killing. Alkaline sucrose density gradient analysis of the ³H-thymine labelled DNA strand showed there was less repair of γ-ray-induced single-strand breaks when BrUra was in the complementary strand. Since there are more of these unrepaired breaks than can be accounted for by BrUra-induced DNA double-strand breakage, some fraction of the lethal events in BrUra-substituted E. coli cells may be unrepaired DNA single-strand breaks.