title: Human abasic endonuclease action on multilesion abasic clusters: implications for radiation-induced biological damage.
abstract: Clustered damages-two or more closely opposed abasic sites, oxidized bases or strand breaks-are induced in DNA by ionizing radiation and by some radiomimetic drugs. They are potentially mutagenic or lethal. High complexity, multilesion clusters (three or more lesions) are hypothesized as repair-resistant and responsible for the greater biological damage induced by high linear energy transfer radiation (e.g. charged particles) than by low linear energy transfer X- or gamma-rays. We tested this hypothesis by assessing human abasic endonuclease Ape1 activity on two- and multiple-lesion abasic clusters. We constructed cluster-containing oligonucleotides using a central variable cassette with abasic site(s) at specific locations, and 5' and 3' terminal segments tagged with visually distinctive fluorophores. The results indicate that in two- or multiple-lesion clusters, the spatial arrangement of uni-sided positive [in which the opposing strand lesion(s) is 3' to the base opposite the reference lesion)] or negative polarity [opposing strand lesion(s) 5' to the base opposite the reference lesion] abasic clusters is key in determining Ape1 cleavage efficiency. However, no bipolar clusters (minimally three-lesions) were good Ape1 substrates. The data suggest an underlying molecular mechanism for the higher levels of biological damage associated with agents producing complex clusters: the induction of highly repair-resistant bipolar clusters.
authors: Biology Department, Brookhaven National Laboratory, Upton, NY 11973-5000, USA.
authors: Brigitte
authors: B
authors: Paap
authors: David M
authors: DM
authors: Wilson
authors: Betsy M
authors: BM
authors: Sutherland
mesh_terms: D004249:DNA Damage; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000378:metabolism*; D005456:Fluorescent Dyes; D006801:Humans; D018499:Linear Energy Transfer; D009841:Oligonucleotides / Q000737:chemistry / Q000378:metabolism; D011839:Radiation, Ionizing
chemical_list: D005456:Fluorescent Dyes; D009841:Oligonucleotides; C085108:APEX1 protein, human; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase