Yields of strand breaks and base lesions in dry plasmid DNA films induced by soft X-rays

Fujii, Kentaro; Yokoya, Akinari; Shikazono, Naoya

To investigate the K-shell photoabsorption effect (photoelectric effect and subsequent secondary electron effect) of DNA damage, dry plasmid DNA (pUC18) films were irradiated with synchrotron monochromatic soft X-rays (270, 435, 560, and 760 eV). Irradiated plasmid DNA was analyzed by agarose gel electrophoresis and the yields of strand breaks were determined by measuring the band intensity of the separated closed circular, open circular and linear forms of the plasmid DNA. The yields of base lesions were determined by the post-irradiation-treatment of the DNA with enzymatic probes (Fpg and Nth) which excise base lesionand visualized it as a strand break. The obtained yields of single strand break (SSB) and the base lesions revealed by enzymatic sensitive sites (ESS) of Fpg and Nth showed the characteristic dependence for photon energy. This result indicates that DNA lesions are induced through varieties of reaction pathways after core-electron ionizations.