Abstract
It has been suggested that the susceptibility of DNA damage to repair strongly depends on the track structure of the radiation represented by a linear-energy transfer (LET) value. In order to clarify the characteristics of complex DNA damage induced by high LET 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; 2 to 900 keV/μm) obtained from JAEA-TIARA and NIRS-HIMAC. In order to focus on the effect of direct energy deposition from radiation track, we prepared hydrated DNA (35 water molecules per nucleotide). Base excision repair enzymes, EndoIII and Fpg, were used to detect oxidative base lesions. The obtained results show that 1) the yield of prompt SSBs did not depend significantly on the LET of the helium ions, 2) whereas the yield of DSBs increased with increasing LET, 3) The yields of isolated nucleobase lesions and clustered damage sites visualized by additionally induced DSB by enzymatic treatment decreased drastically with increasing LET, and 4) very few enzyme-sensitive sites were induced above 100 keV/μm. 5) C and Ne ions induce less base lesions than He ions when compared in the same LET region. These results indicate that the yield of cluster of nucleobase lesions, which are less readily processed by the base excision repair proteins, depends not only on LET but also ion species irradiated.
