title: DNA repair excision nuclease attacks undamaged DNA. A potential source of spontaneous mutations.
abstract: Nucleotide excision repair is a general repair system that eliminates many dissimilar lesions from DNA. In an effort to understand substrate determinants of this repair system, we tested DNAs with minor backbone modifications using the ultrasensitive excision assay. We found that a phosphorothioate and a methylphosphonate were excised with low efficiency. Surprisingly, we also found that fragments of 23-28 nucleotides and of 12-13 nucleotides characteristic of human and Escherichia coli excision repair, respectively, were removed from undamaged DNA at a significant rate. Considering the relative abundance of undamaged DNA in comparison to damaged DNA in the course of the life of an organism, we conclude that, in general, excision from and resynthesis of undamaged DNA may exceed the excision and resynthesis caused by DNA damage. As resynthesis is invariably associated with mutations, we propose that gratuitous repair may be an important source of spontaneous mutations.
authors.affiliation: Department of Biochemistry and Biophysics, Mary Ellen Jones Bldg., University of North Carolina School of Medicine, Chapel Hill, NC 27599, USA.
authors.forename: M E
authors.initials: ME
authors.lastname: Branum
authors.forename: J T
authors.initials: JT
authors.lastname: Reardon
authors.forename: A
authors.initials: A
authors.lastname: Sancar
mesh_terms: D001483:Base Sequence; D004249:DNA Damage; D004260:DNA Repair; D004269:DNA, Bacterial / Q000096:biosynthesis; D003851:Deoxyribonucleases / Q000378:metabolism*; D004926:Escherichia coli; D006147:Guanine / Q000031:analogs & derivatives* / Q000378:metabolism; D006801:Humans; D008956:Models, Chemical; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics*; D009943:Organophosphorus Compounds / Q000378:metabolism
chemical_list: D004269:DNA, Bacterial; D009943:Organophosphorus Compounds; C032627:methylphosphonic acid; C024829:8-hydroxyguanine; D006147:Guanine; D003851:Deoxyribonucleases