title: Efficiency of radiation-induced base lesion excision and the order of enzymatic treatment.
abstract: 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.
  
  
  
  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.
  
  
  
  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.
  
  
  
  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.
authors.affiliation: a Department of Environmental Sciences, Faculty of Science , Ibaraki University , Mito , Ibaraki , Japan.|b Tokai Quantum Beam Science Center, Quantum Beam Science Research Directorate, National Institutes of Quantum and Radiological Science and Technology , Tokai-mura , Ibaraki , Japan.
authors.forename: Iyo
authors.initials: I
authors.lastname: Shiraishi
authors.affiliation: 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.
authors.forename: Naoya
authors.initials: N
authors.lastname: Shikazono
authors.affiliation: 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.
authors.forename: Masao
authors.initials: M
authors.lastname: Suzuki
authors.affiliation: b Tokai Quantum Beam Science Center, Quantum Beam Science Research Directorate, National Institutes of Quantum and Radiological Science and Technology , Tokai-mura , Ibaraki , Japan.
authors.forename: Kentaro
authors.initials: K
authors.lastname: Fujii
authors.affiliation: a Department of Environmental Sciences, Faculty of Science , Ibaraki University , Mito , Ibaraki , Japan.|b Tokai Quantum Beam Science Center, Quantum Beam Science Research Directorate, National Institutes of Quantum and Radiological Science and Technology , Tokai-mura , Ibaraki , Japan.
authors.forename: Akinari
authors.initials: A
authors.lastname: Yokoya
mesh_terms: D020029:Base Pairing / Q000528:radiation effects; D004247:DNA / Q000737:chemistry* / Q000528:radiation effects*; D004249:DNA Damage; D045647:DNA Glycosylases / Q000737:chemistry* / Q000528:radiation effects; D004260:DNA Repair; D003850:Deoxyribonuclease I / Q000737:chemistry* / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D011829:Radiation Dosage
chemical_list: D004247:DNA; D003850:Deoxyribonuclease I; D045647:DNA Glycosylases
keywords: Base excision repair; base lesions; clustered DNA damage; high-LET radiation