Irradiated Energy Dependence of molecular changes to plasmid DNA induced by monochromatic soft X-rays

Fujii, Kentaro; Shikazono, Naoya; Yokoya, Akinari

In order to verify the possibility of selective damage induction in DNA, the yields of base lesions as well as strand breaks have been measured in dry plasmid DNA films irradiated with highly monochromatized soft X-rays in the energy region of 270-760eV. The experiments were performed at the beamline BL23SU in the SPring-8. The yields of base lesions were determined by the post-irradiation-treatment of the DNA with enzymatic probes (Fpg and Endo III) which excise base lesion. The yields of both pyrimidine and purine base lesions, observed as Nth-sensitive and Fpg-sensitive sites, respectively, are strikingly high at the oxygen K-edge (560eV) but extremely low at an energy just below the nitrogen K-edge (380eV) as compared with the yields observed at other photon energies.