In this issue of Radiation Research, we would like to call your attention to the work of Cecchini et al. (1). This elegant effort brings a new understanding to the action of well-known cellular radiosensitizer, 5-bromodeoxyuridine.

Earlier efforts in model systems had shown that halouracils, including 5-bromouracil, capture relatively harmless radiation-produced electrons when incorporated in DNA. The unstable anion radical intermediate then undergoes halide ion loss and creates a very damaging uracil-5-yl radical. This earlier work indicated that this reactive radical produces strand breaks by hydrogen abstraction from the deoxyribose phosphate backbone. There have been questions about this mechanism because in some model systems the halide ion loss was not found.

Cecchini et al. use defined-sequence oligonucleotides and some inventive experiments to create a breakthrough in our understanding that adds an important new twist to this story. 5-Bromodeoxyuridine incorporated in oligonucleotides is not...

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