Iyo Shiraishi1,2, Naoya Shikazono3, Masao Suzuki4, Kentaro Fujii2, Akinari Yokoya1,2. 1. a Department of Environmental Sciences, Faculty of Science , Ibaraki University , Mito , Ibaraki , Japan. 2. b Tokai Quantum Beam Science Center, Quantum Beam Science Research Directorate, National Institutes of Quantum and Radiological Science and Technology , Tokai-mura , Ibaraki , Japan. 3. c Department of Quantum Beam Life Science , Quantum Beam Science Research Directorate, National Institutes of Quantum and Radiological Science and Technology , Kyoto, Kizugawa-shi , Japan. 4. d Department of Basic Medical Sciences for Radiation Damages , National Institute of Radiological Sciences, National Institutes of Quantum and Radiological Science and Technology , Chiba , Japan.
Abstract
PURPOSE: To clarify whether initial base excision repair processes at clustered DNA damage sites comprising multiple base lesions affect subsequent excision processes via the formation of additional strand breaks by glycosylase and apurinic/apyrimidinic (AP) endonuclease base excision enzymes. MATERIALS AND METHODS: Plasmid DNA (pUC18) as a model DNA molecule was exposed to high-linear-energy-transfer (LET) ionizing radiation (He2+ or C6+ ions) or low-LET ionizing radiation (X-rays) under various conditions to produce varied radical-scavenging effects. pUC18 was then treated sequentially or simultaneously with two bacterial base excision enzymes (glycosylases), namely, endonuclease III and formamidopyrimidine-DNA glycosylase, which convert pyrimidine (or abasic [AP] site) and purine (or AP site) lesions to single-strand breaks (SSB), respectively. Yields of additional SSB or double-strand breaks (DSB) as digestion products were examined after changing the order of enzymatic treatment. RESULTS: There were few differences among the enzymatic treatments, indicating that treatment order did not affect the final yields of additional SSB or DSB formed by glycosylase activity. This suggests that of the total damage, the fraction of clustered damage sites with a persistent base lesion dependent on the order of glycosylase treatment was insignificant if present. CONCLUSION: Base lesion clusters induced by high- or low-LET radiation appear three or more base pairs apart, and are promptly converted to a DSB by glycosylase, regardless of the order of enzymatic treatment.
PURPOSE: To clarify whether initial base excision repair processes at clustered DNA damage sites comprising multiple base lesions affect subsequent excision processes via the formation of additional strand breaks by glycosylase and apurinic/apyrimidinic (AP) endonuclease base excision enzymes. MATERIALS AND METHODS: Plasmid DNA (pUC18) as a model DNA molecule was exposed to high-linear-energy-transfer (LET) ionizing radiation (He2+ or C6+ ions) or low-LET ionizing radiation (X-rays) under various conditions to produce varied radical-scavenging effects. pUC18 was then treated sequentially or simultaneously with two bacterial base excision enzymes (glycosylases), namely, endonuclease III and formamidopyrimidine-DNA glycosylase, which convert pyrimidine (or abasic [AP] site) and purine (or AP site) lesions to single-strand breaks (SSB), respectively. Yields of additional SSB or double-strand breaks (DSB) as digestion products were examined after changing the order of enzymatic treatment. RESULTS: There were few differences among the enzymatic treatments, indicating that treatment order did not affect the final yields of additional SSB or DSB formed by glycosylase activity. This suggests that of the total damage, the fraction of clustered damage sites with a persistent base lesion dependent on the order of glycosylase treatment was insignificant if present. CONCLUSION: Base lesion clusters induced by high- or low-LET radiation appear three or more base pairs apart, and are promptly converted to a DSB by glycosylase, regardless of the order of enzymatic treatment.
Entities:
Keywords:
Base excision repair; base lesions; clustered DNA damage; high-LET radiation
Authors: Ying Gao; Changling Li; Leizhen Wei; Yaqun Teng; Satoshi Nakajima; Xiukai Chen; Jianquan Xu; Brittany Leger; Hongqiang Ma; Stephen T Spagnol; Yong Wan; Kris Noel Dahl; Yang Liu; Arthur S Levine; Li Lan Journal: Cancer Res Date: 2017-04-17 Impact factor: 12.701