Radiation Chemistry of DNA

Relevant structural and mechanistic information has been gained during the last decade on the main photo-and radiation-induced damage to isolated DNA [for recent comprehensive reviews, see 1-7]. This was mostly achieved using nucleosides and short oligonucleotides as DNA model compounds. Extrapolation to cellular DNA is still a matter of debate, particularly for ionizing radiation. In fact, there is still a paucity of relevant and accurate data on the formation of radiation-induced base damage to DNA in cells and tissues. In addition, there is a lack of both qualitative and quantitative information on the spectrum of UV-B-induced DNA lesions. This may be accounted for by the still challenging analytical problem associated with the measurement of photo-and radiation-induced damage to DNA [8]. In this respect, it should be mentioned that most of the determination of radiation-induced base damage using the gas-chromatographymass spectrometry (GC-MS) assay developed initially by Dizdaroglu et al. [9-11], has to be reassessed. This also applies to the bulk of DNA repair studies of radiation-induced base damage where the specificity of recognition of several DNA-glycosylases was evaluated using the above GC-MS method. Emphasis was placed in this survey on mechanistic aspects of the photo-and radiation-induced decomposition of the base moieties of DNA and model compounds that recently became available. These mostly include the reaction pathways associated with exposure of the guanine (Gua) base of DNA and related model systems to both the direct and indirect effects of ionizing radiation. Relevant information is also provided on both the type I and type II photosensitized reactions of the guanine moiety of DNA which are involved in the effects of the UV-A component of solar light [7]. As a second major topic to be addressed, the main available methods aimed at measuring individual damage within DNA and isolated cells are critically reviewed.