title: Repair and misrepair of site-specific DNA double-strand breaks by human cell extracts.
abstract: The rejoining by human cell extracts of a double-strand break induced by endonuclease treatment at one of several sites within a small DNA molecule was studied. Rejoining was found at each of 8 sites tested, but the rejoin efficiency varied with the nature of the break (e.g., breaks with cohesive ends were rejoined more efficiently than blunt-ended breaks). Extracts from primary and immortalized cell lines, as well as those from individuals with ataxia telangiectasia (A-T), showed the same pattern of relative rejoin efficiencies. However, mis-rejoining varied with the cell extract used, and was particularly elevated with two immortalized A-T cell lines. Mixing experiments showed that the mis-rejoining property of extracts could act in a semi-dominant fashion, depending on the individual efficiencies of the component extracts. The mis-rejoin mechanism involved deletion at sites of short direct repeats at various distances from the initial break site. A model of deletion formation (the strand-exposure and repair model) is restated to explain the sequence repeat dependence found, and is compared to models of homologous DNA recombination.
authors.affiliation: Cell and Molecular Biology Division, MRC Radiobiology Unit, Didcot, Oxon, UK.
authors.forename: A
authors.initials: A
authors.lastname: Ganesh
authors.forename: P
authors.initials: P
authors.lastname: North
authors.forename: J
authors.initials: J
authors.lastname: Thacker
mesh_terms: D001260:Ataxia Telangiectasia; D001482:Base Composition; D001483:Base Sequence; D002460:Cell Line; D002474:Cell-Free System; D003001:Cloning, Molecular / Q000379:methods; D004247:DNA / Q000235:genetics*; D004249:DNA Damage; D004260:DNA Repair; D004262:DNA Restriction Enzymes / Q000378:metabolism; D006801:Humans; D008957:Models, Genetic; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010957:Plasmids; D015183:Restriction Mapping; D013379:Substrate Specificity
chemical_list: D004247:DNA; D004262:DNA Restriction Enzymes