Difference in the induction, but not in the repair, of X-ray- and nitrogen ion-induced DNA single-strand breaks as measured using human cell extracts

• PURPOSE: To compare the repair efficiency of X-ray (low linear energy transfer [LET]) and nitrogen ion (high LET)-induced single-strand breaks (SSB) in a human cell-free end-joining system. MATERIALS AND METHODS: SSB were introduced into a bacterial plasmid, pBR322, by X-rays (4 MeV photons) and nitrogen ions with an LET=125 keV micro m(-1). Repair efficiency was studied under incubation with the protein extracts from human squamous carcinoma cells, UT-SCC-5. RESULTS: A several fold higher dose of nitrogen ion radiation compared with X-ray radiation was needed to induce a similar loss of supercoiled plasmid DNA. There was no difference in the repair efficiency of SSB induced by these two types of radiation. CONCLUSION: The data indicate that X-rays at 25 Gy and nitroging ions at 100 Gy radiation doses, under condition of low scavenging capacity (10 mM Tris), induce SSB of similar complexity or, alternatively, differences in SSB complexity do not alter the repair rate.

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