title: Double-strand gap repair results in homologous recombination in mouse L cells.
abstract: Previous studies have demonstrated that the presence of double-strand breaks or double-strand gaps increases the frequency of homologous recombination between two cotransferred DNAs when they are introduced into cultured mammalian cells. Here we demonstrate that the repair of these double-strand gaps is a major mechanism for homologous recombination between exogenous DNAs. In particular, when a plasmid DNA containing a 104-base-pair (bp) gap in its tk gene (herpes simplex virus gene for thymidine kinase) undergoes recombination in mouse L cells to generate an intact gene, the majority of events result from direct repair of the double-strand gap using a cotransferred DNA as the template. We analyzed the recombination events by comparing the frequency of tk+ colonies, Southern blotting of cloned tk+ cell lines, and cloning recombined functional tk genes by plasmid rescue. In addition, by creating double-strand breaks within or adjacent to heterologous insertions in a mutant tk gene, we estimate that the L cell can generate a double-strand gap of between 152 and 248 bp and then can repair the gap to create a functional tk gene. We conclude that double-strand breaks and double-strand gaps are recombinogenic in transferred plasmid DNAs because they serve as intermediates in homologous recombination by double-strand gap repair, a nonreciprocal exchange of DNA or gene conversion event.
mesh_terms: D000818:Animals; D003001:Cloning, Molecular; D004260:DNA Repair; D004262:DNA Restriction Enzymes; D005785:Gene Conversion; D007739:L Cells / Q000378:metabolism; D051379:Mice; D010957:Plasmids; D011994:Recombinant Proteins / Q000235:genetics; D011995:Recombination, Genetic; D012689:Sequence Homology, Nucleic Acid; D018139:Simplexvirus / Q000235:genetics; D013937:Thymidine Kinase / Q000235:genetics; D014764:Viral Proteins / Q000235:genetics
chemical_list: D011994:Recombinant Proteins; D014764:Viral Proteins; D013937:Thymidine Kinase; D004262:DNA Restriction Enzymes