Radiation-Induced Strand Breaks in DNA: Chemical and Enzymatic Analysis of End Groups and Mechanistic Aspects

Abstract

Publisher Summary This chapter reviews the results of chemical and enzymatic analyses of radiation-induced strand breaks together that allows proposing a detailed mechanism of DNA strand break formation by ionizing radiation. Chemical analysis enables one to describe radiation-induced reactions, and the final structure of the sugar moiety and enzymatic analysis determines the biochemical reactivity of the end groups on the 3’ or 5’ terminal of the strand break. Enzymatic methods may be more sensitive than chemical analysis, but it has become evident that both approaches are necessary for an understanding of the mechanisms of radiation-induced strand breakage in DNA. Exposure of DNA to ionizing radiation produces an interruption of the nucleotide strand that can be considered as an important lesion responsible for the inactivation of the biological function of DNA. The chapter describes an experimental work that leads to a detailed understanding of the chemical structure of radiation-induced strand breaks and to knowledge of the mechanisms of their formation. The application of different techniques such as pulse radiolysis, ESR spectroscopy, product analysis in one laboratory, and sedimentation and enzymatic analysis in another laboratory lead to comparable conclusions. The chapter describes the frequency of strand breaks under various radiation conditions for DNA in aqueous solution, in dry DNA, and in cells. The presence of intact hydroxyl or phosphate end groups on DNA strand breaks can be demonstrated by a variety of enzymes each of which reacts specifically with a certain end group on the 3’ terminal or on the 5’ terminal. The chapter also describes the details of the specificity of these enzymes and their reactivity with respect to radiation-induced strand breaks.