title: Increased mutability and decreased repairability of a three-lesion clustered DNA-damaged site comprised of an AP site and bi-stranded 8-oxoG lesions.
abstract: OBJECTIVE
  Ionizing radiation induces DNA damage, some of which are present in clusters, defined as two or more lesions within one to two helical turns of DNA by passage of a single radiation track. These clusters are thought to contribute to the detrimental effects of radiation, in part due to the compromised repair of clustered DNA damaged sites.
  
  
  METHODS
  The repair of three-lesion cluster present in oligonucleotides were determined in vitro using the hamster cell line CHO-K1 nuclear extract or purified proteins involved in base excision repair. The mutagenic potential of these clusters present in a plasmid was determined using an Escherichia coli reporter assay.
  
  
  RESULTS
  We have shown that the repair of an abasic (AP) site within a three-lesion cluster, comprised of an AP site and bi-stranded 8-oxo-7,8-dihydroguanine (8-oxoG) lesions, is retarded compared to that of an isolated AP site in an in vitro base excision repair (BER) assay. Further, the mutation frequency of the clustered damaged site is up to three times greater than that of an isolated 8-oxoG lesion.
  
  
  CONCLUSIONS
  As a consequence of enhanced mutagenic potential of clusters, non-double-strand break (DSB) DNA damage may contribute to the detrimental effects of radiation, in addition to the effects of DSB.
authors.affiliation: Gray Institute for Radiation Oncology and Biology, Department of Oncology, University of Oxford , Oxford , UK.
authors.forename: Siobhan
authors.initials: S
authors.lastname: Cunniffe
authors.forename: Alexandra
authors.initials: A
authors.lastname: Walker
authors.forename: Robert
authors.initials: R
authors.lastname: Stabler
authors.forename: Peter
authors.initials: P
authors.lastname: O'Neill
authors.forename: Martine E
authors.initials: ME
authors.lastname: Lomax
mesh_terms: D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D004247:DNA / Q000737:chemistry / Q000235:genetics / Q000528:radiation effects; D004249:DNA Damage / Q000235:genetics; D004260:DNA Repair / Q000235:genetics; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics / Q000528:radiation effects; D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics / Q000528:radiation effects; D006147:Guanine / Q000031:analogs & derivatives / Q000737:chemistry / Q000528:radiation effects; D009154:Mutation
chemical_list: D004269:DNA, Bacterial; C024829:8-hydroxyguanine; D006147:Guanine; D004247:DNA
keywords: 8-oxoG; AP site; Clustered DNA damage; base excision repair; mutagenic potential