LET dependence of the yield of single-, double-strand breaks and base lesions in fully hydrated plasmid DNA films by He ion irradiation

Urushibara, Ayumi*; Shikazono, Naoya; O'Neill, P.*; Fujii, Kentaro; Wada, Seiichi*; Yokoya, Akinari

To characterize the complexity of radiation damage to DNA, fully hydrated plasmid DNA was irradiated with He ions. From quantification of the conformational changes of the irradiated samples, the yields of single-(SSB) and double strand break (DSB) were obtained. Base lesions were visualized as additional strand breaks by treatment with base excision repair enzymes. The yield of prompt SSBs does not depend significantly on LET of the He ions, whereas the yield of prompt DSBs increases with increasing LET. The yields of isolated base lesions, revealed by enzymes as additional SSBs, decrease drastically with increasing LET. The sum of the yields of DSB and additional DSBs revealed by the enzymes increase with increasing LET of the He ions except at the highest LET investigated. These results indicate that the yields of clustered damage, revealed as DSB and non-DSB clustered damage sites, increase with increasing ionization density of radiation.