Abstract
The goal of our study is to clarify the nature of DNA damage in relation to track structure of radiation. The yields of single- and double-strand breaks (SSB and DSB), base lesions and clustered damage induced in closed-circular plasmid DNA (pUC18) were measured after exposing to various kinds of radiation (He, Ne and C ions; 20 to 500 keV/m, soft X-rays; 150 kVp). To focus on the effect of direct energy deposition from radiation track, we prepared hydrated DNA (35 water molecules per nucleotide) as well as solution sample with various scavenging capacities. Base excision repair enzymes, EndoIII and Fpg, were used to detect oxidative base lesions. The obtained results show that 1) the yield of directly induced SSB by the soft X-irradiation is about 30 % of total SSB yields induced in a cell mimetic condition and 2) the SSB yield does not significantly depend on the quality of radiation, whereas DSBs are induced at relatively higher yield by both higher LET ion- and soft X-irradiation. On the other hand, 3) the yields of base lesions show a maximum by soft X- irradiation and drastically decreases with increasing of LET. 4) Soft X-ray photons are more effective in inducing base lesions than ions with similar LET, and 5) EndoIII treatment gives significantly higher yield of base lesion than Fpg treatment for all irradiation samples. The mechanism of DNA damage induction by various kinds of radiation will be discussed by comparing the experimental results with track structures examined by computational simulation studies.
