title: Nucleosomes suppress the formation of double-strand DNA breaks during attempted base excision repair of clustered oxidative damages.
abstract: Exposure to ionizing radiation can produce multiple, clustered oxidative lesions in DNA. The near simultaneous excision of nearby lesions in opposing DNA strands by the base excision repair (BER) enzymes can produce double-strand DNA breaks (DSBs). This attempted BER accounts for many of the potentially lethal or mutagenic DSBs that occur in vivo. To assess the impact of nucleosomes on the frequency and pattern of BER-dependent DSB formation, we incubated nucleosomes containing oxidative damages in opposing DNA strands with selected DNA glycosylases and human apurinic/apyrimidinic endonuclease 1. Overall, nucleosomes substantially suppressed DSB formation. However, the degree of suppression varied as a function of (i) the lesion type and DNA glycosylase tested, (ii) local sequence context and the stagger between opposing strand lesions, (iii) the helical orientation of oxidative lesions relative to the underlying histone octamer, and (iv) the distance between the lesion cluster and the nucleosome edge. In some instances the binding of a BER factor to one nucleosomal lesion appeared to facilitate binding to the opposing strand lesion. DSB formation did not invariably lead to nucleosome dissolution, and in some cases, free DNA ends resulting from DSB formation remained associated with the histone octamer. These observations explain how specific structural and dynamic properties of nucleosomes contribute to the suppression of BER-generated DSBs. These studies also suggest that most BER-generated DSBs will occur in linker DNA and in genomic regions associated with elevated rates of nucleosome turnover or remodeling.
authors.affiliation: From the Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, Vermont 05405.
authors.forename: Wendy J
authors.initials: WJ
authors.lastname: Cannan
authors.affiliation: From the Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, Vermont 05405.
authors.forename: Betty P
authors.initials: BP
authors.lastname: Tsang
authors.affiliation: From the Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, Vermont 05405.
authors.forename: Susan S
authors.initials: SS
authors.lastname: Wallace
authors.affiliation: From the Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, Vermont 05405 david.pederson@uvm.edu.
authors.forename: David S
authors.initials: DS
authors.lastname: Pederson
mesh_terms: D002843:Chromatin / Q000737:chemistry / Q000378:metabolism / Q000528:radiation effects; D004247:DNA / Q000737:chemistry / Q000378:metabolism / Q000528:radiation effects; D053903:DNA Breaks, Double-Stranded; D004249:DNA Damage; D045647:DNA Glycosylases / Q000378:metabolism; D004260:DNA Repair / Q000502:physiology*; D043224:Deoxyribonuclease (Pyrimidine Dimer) / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009707:Nucleosomes / Q000378:metabolism*; D010084:Oxidation-Reduction
chemical_list: D002843:Chromatin; D009707:Nucleosomes; D004247:DNA; D043224:Deoxyribonuclease (Pyrimidine Dimer); C468347:NTHL1 protein, human; D045647:DNA Glycosylases; C479058:oxoguanine glycosylase 1, human
keywords: Base Excision Repair (BER); Chromatin; DNA Double-strand Break Formation; DNA Enzyme; DNA Glycosylases; DNA Repair; Histone; Ionizing Radiation; Nucleosomes; Oxygen Radicals