title: Molecular analysis of base damage clustering associated with a site-specific radiation-induced DNA double-strand break.
abstract: Base damage flanking a radiation-induced DNA double-strand break (DSB) may contribute to DSB complexity and affect break repair. However, to date, an isolated radiation-induced DSB has not been assessed for such structures at the molecular level. In this study, an authentic site-specific radiation-induced DSB was produced in plasmid DNA by triplex forming oligonucleotide-targeted (125)I decay. A restriction fragment terminated by the DSB was isolated and probed for base damage with the E. coli DNA repair enzymes endonuclease III and formamidopyrimidine-DNA glycosylase. Our results demonstrate base damage clustering within 8 bases of the (125)I-targeted base in the DNA duplex. An increased yield of base damage (purine > pyrimidine) was observed for DSBs formed by irradiation in the absence of DMSO. An internal control fragment 1354 bp upstream from the targeted base was insensitive to enzymatic probing, indicating that the damage detected proximal to the DSB was produced by the (125)I decay that formed the DSB. Gas chromatography-mass spectrometry identified three types of damaged bases in the approximately 32-bp region proximal to the DSB. These base lesions were 8-hydroxyguanine, 8-hydroxyadenine and 5-hydroxycytosine. Finally, evidence is presented for base damage >24 bp upstream from the (125)I-decay site that may form via a charge migration mechanism.
authors.affiliation: Department of Nuclear Medicine, Warren Grant Magnuson Clinical Center, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Kamal
authors.initials: K
authors.lastname: Datta
authors.forename: Pawel
authors.initials: P
authors.lastname: Jaruga
authors.forename: Miral
authors.initials: M
authors.lastname: Dizdaroglu
authors.forename: Ronald D
authors.initials: RD
authors.lastname: Neumann
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Winters
mesh_terms: D001483:Base Sequence / Q000528:radiation effects*; D004247:DNA / Q000737:chemistry* / Q000528:radiation effects*; D053903:DNA Breaks, Double-Stranded / Q000528:radiation effects*; D004260:DNA Repair / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D008969:Molecular Sequence Data; D009711:Nucleotides / Q000737:chemistry* / Q000528:radiation effects*; D011829:Radiation Dosage
chemical_list: D009711:Nucleotides; D004247:DNA