Induction of strand breaks and base lesions in dry plasmid DNA films induced by 270 - 560 eV ultrasoft X-rays

Fujii, Kentaro; Yokoya, Akinari; Shikazono, Naoya

To investigate the direct effect of constituent atoms on DNA damage, dry plasmid DNA (pUC18) films were irradiated with synchrotron monochromatic ultrasoft X-rays. Four photon energies, 270, 380, 435, and 560eV, a value below the carbon K-edge, below and above the nitrogen K-edge, and above the oxygen K-edge, respectively, were chosen for the irradiation experiments. Irradiated plasmid DNA was analyzed by agarose gel electrophoresis and the yields of strand breaks were determined by measuring the band intensities of the separated closed circular, open circular and linear forms of the plasmid DNA. The yields of base lesions and clustered damage site including at least one base lesion were determined by the post-irradiation-treatment of the DNA with enzymatic probes (Fpg and Endo III) which convert base lesions into detectable strand breaks.