Strand break formation in plasmid DNA irradiated by nanosecond XUV-laser pulses

The development of the desktop, repetitive XUV laser based on collisionally pumped transition of Ne-like Ar ions in a pinching capillary discharge [1] is of interest for numerous applications in radia-tion biophysics. Ionizing radiation induces a variety of DNA damages including single-strand breaks (SSBs), double-strand breaks (DSBs), abasic sites, modified sugar and bases. Most theoretical and ex-perimental studies have been focused on DNA strand scissions, in particular production of DNA double-strand breaks. The complexity of lesions produced in DNA by ionizing radiations is thought to depend on the amount of energy deposited at the site of each lesion. We have studied the nature of DNA damage induced directly by the pulsed 46.9 nm radiation provided by a capillary-discharge Ne-like Ar laser (CDL). Different surface doses were delivered with a repetition rate of a few Hz and an average pulse energy ~ 1 μJ. A simple model DNA molecule, i.e., dried closed-circular plasmid DNA (pBR322), was irradiated. The agarose gel electro-phoresis method was used for determination of both SSB and DSB yields.