Direct measurements of DNA fragmentation induced by heavy ions

Unrepaired double-strand breaks (DSB) in the sugarphosphate backbone of the DNA molecule resulting from exposure of cells to ionising radiation are believed to be critical lesions that can lead to cell killing, mutation and carcinogenesis. Moreover, the pattern of DNA fragmentation is directly related to radiation track structure and, in the case of high-LET radiation, becomes determined by the spatial localisation of ionising events near the centre of the track. [1] Recent pulsed field electrophoresis data have confirmed that the induction of DSBs after high LET irradiation is non-randomly located along DNA and forms clusters of multiply damaged sites that split the DNA helix into a set of small fragments [2]. However, production of multiply fragmented DNA is difficult to assess by conventional methods, since these assays usually can not resolve DNA fragments below 1 kbp. In contrast, by use of Atomic Force Microscopy (AFM), it is possible to directly visualise the damage provoked by radiation.