Repairable and Irrepairable Damage in 5-bromouracil-substituted DNA Exposed to Ultra-violet Radiation

Abstract

Photochemical damage produced by u.v.-irradiation was studied in normal and 5-bromouracil-substituted DNA (BU-DNA) of mammalian cells in relation to repair processes known to occur in these cells. The main photoproduct of incorporated bromouracil was identified as uracil, accompanied by a single-strand break in the DNA chain. Uracil was excised from the DNA and the break was rejoined at a rate much faster than the excision of pyrimidine dimers from unsubstituted DNA. Therefore, the sensitizing action of the halogenated compound was not ascribed to an overall increase of base damage but to qualitatively different lesions in BU-DNA, viz. Double strand breaks and DNA-protein crosslinks.