title: Two clustered 8-oxo-7,8-dihydroguanine (8-oxodG) lesions increase the point mutation frequency of 8-oxodG, but do not result in double strand breaks or deletions in Escherichia coli.
abstract: Multiply damaged sites (MDSs) are generated in DNA by ionizing radiation. In vitro studies predict that base excision repair in cells will convert MDSs to lethal double strand breaks (DSBs) when two opposing base damages are situated >/=2 bp apart. If the lesions are situated immediately 5' or 3' to each other, repair is predicted to occur sequentially due to inhibition of the DNA glycosylase by a single strand break repair intermediate. In this study, we examined how the distance between two opposing lesions alters the mutation frequency of an 8-oxodG in an MDS, and whether repair generates DSBs and deletions in bacteria. The 8-oxodG mutation frequency declined in MutY-deficient bacteria when the opposing 8-oxodG was 6 bp away, and was similar to a single 8-oxodG when the lesions were separated by 14 bp. However, the number of deletions detected for the MDSs was equivalent to the undamaged sequence. Using a separate assay, MDSs consisting of two 8-oxodG or an 8-oxodG opposite a uracil were not converted to DSBs in the absence of DNA replication in wild-type and transcription-coupled repair-deficient bacteria. This is the first study showing that DSB-repair intermediates and deletions are not formed during repair of clustered 8-oxodGs in cells.
authors.affiliation: Department of Molecular and Cellular Physiology and the Feist-Weiller Cancer Center, Louisiana Health Sciences Center, 1501 Kings Highway, Shreveport, LA 71130, USA.
authors.forename: Svitlana
authors.initials: S
authors.lastname: Malyarchuk
authors.forename: Katherine L
authors.initials: KL
authors.lastname: Brame
authors.forename: Reneau
authors.initials: R
authors.lastname: Youngblood
authors.forename: Runhua
authors.initials: R
authors.lastname: Shi
authors.forename: Lynn
authors.initials: L
authors.lastname: Harrison
mesh_terms: D004249:DNA Damage; D004260:DNA Repair; D004261:DNA Replication; D004926:Escherichia coli / Q000235:genetics*; D005787:Gene Frequency; D006147:Guanine / Q000031:analogs & derivatives* / Q000032:analysis*; D008156:Luciferases / Q000032:analysis; D010957:Plasmids / Q000737:chemistry; D017354:Point Mutation; D017384:Sequence Deletion; D014158:Transcription, Genetic
chemical_list: C024829:8-hydroxyguanine; D006147:Guanine; D008156:Luciferases