Critical energies for SSB and DSB induction in plasmid DNA: Studies using synchrotron radiation

The most frequent energy depositions along the charged-particle tracks associated with high-energy ionizing radiations are on the order of 10's of eV. There continues to be a need for experimental data that relate the magnitudes of energy-deposition events to the molecular damages that result from them. The energy range between a few and several hundred eV is of particular importance. In addition, the determination of the yields of various types of damage induced in DNA as functions of the energy deposited in it (action spectra) may provide useful insights into the initial pathways of lesion induction. With much interest currently focused on the role of lesion complexity in relation to biological effectiveness, it is important to know to what extent single energy deposition events can independently initiate damages involving more than one molecular site, for example a DNA dsb. This paper reports some of the experimental methods and initial data, also with dry plasmid DNA, obtained using VUV from a synchrotron radiation source at selected energies in the range 7 to 25 eV, determining action spectra for ssb and dsb induction