Abstract
Types of DNA damage induced by ionizing radiation are characterized as base modifications, strand breaks and crosslinking. It is well known that these damages are induced mostly by hydroxyl radical. Hydroxyl radical is thought to attack DNA bases more extensively than the sugar phosphate backbone of DNA; however, one fifth of hydroxyl radicals attack DNA backbone to produce the scission of deoxyribose phosphate bonds, leading to single and double strand breaks. If not repaired, double strand breaks (DSB) may lead to cell death, genomic instability, and carcinogenesis. Thus, studies of the formation mechanisms of DSB induced by ionizing radiation are of utmost importance.
Recently, by controlling DNA structures in aqueous solutions, we produced compactly folded DNA and unfolded forms of DNA by addition of polyamine compounds. We selected T4 DNA as a suitable model for the observation of higher-order structures of DNA. We irradiated dilute DNA solutions having different structures by cobalt 60 gamma rays. DSBs induced by gamma rays were observed using fluorescence microscopic technology. In this work, we will present the technical details of our studies, and the results of the relationships between the higher-order structures of DNA and DNA damage by ionizing radiation.
