Yields of DNA strand breaks and base lesions induced by oxygen K-shell electron ionization

Sugaya, Yuki* ; Fujii, Kentaro; Yokoya, Akinari

We have tried oxygen selective damage induction in DNA by tuning soft X-ray energy. Thin DNA films of closed circular plasmid (pUC18) without any additives were prepared and tested the stability of DNA in the film by observing conformational changes using gel electrophoresis. We performed soft X-ray irradiation to the films at BL23SU in SPring-8. The yields of strand breaks, base lesions, as well as AP sites produced by irradiation of several soft X-ray energies around oxygen K-shell ionization threshold. The yields of base lesions and AP sites are determined by post-irradiation-treatment of the DNA with enzymatic probes. The yield of AP site, as well as those of other lesions, shows a minimum at the resonance excitation energy (538 eV) absorbed by the sample with a highest probability. The results indicate that the resonance excitation of 1s electron does not rather enhance the DNA damage induction.