The induction if DNA single and double strand breaks in DNA by ionising radiation
Melvyn Folkard and Kevin Prise
Gray Cancer Institute, PO Box 100, Mount Vernon Hospital, Northwood, HA6 2JR, UK
One of the goals of radiation biophysics is to develop a mechanistic model of how ionizing radiations interact with living tissues, from the initial energy deposition event at the molecular level, through to the longer-term consequences for the whole organism. At the Gray Cancer Institute, a number of strategies are being used to address this goal. For example, we have devised experiments to quantify the amount of energy involved in the induction of ‘strand-breaks’ in DNA. The formation of strand breaks is known to be the critical step that can lead to observable effects at the cell and tissue level. The approach we have developed is to expose DNA to low energy ionizing radiation at a range of energies and look for thresholds, below which single strand and double strand breaks are not produced. Our target molecule for these studies is extracted and purified plasmid DNA, which assumes a different topology depending on the damage it receives. The different forms of DNA can be readily quantified by gel electrophoresis, such that it is relatively straightforward to measure the fraction of induced single-strand and double-strand breaks. Our most recent studies have involved the use of a novel ‘wet cell’ that permits the exposure of DNA in solution to vacuum UV energies below 10eV. Even at these low energies, we find that single and double strand breaks are readily induced in DNA, and that indirect damage through the formation of radicals in the water is an important pathway.
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