title: A partial hprt gene duplication generated by non-homologous recombination in V79 Chinese hamster cells is eliminated by homologous recombination.
abstract: Here, the sequence in the hprt gene of the duplication mutant SPD8 originating from V79 Chinese hamster cells was determined. The duplication arose after non-homologous recombination between exon 6 and intron 7, resulting in an extra copy of the 3' portion of exon 6, of exon 7 and of flanking intron regions. Only a duplication of exon 7 is present in the mRNA, since the duplicated exon 6 lacks its 5' splice site and is removed during RNA processing. The findings in this study suggest that the non-homologous recombination mechanism which occurred here may have been initiated by endonucleases, rather than by a spontaneous double strand break. Subsequently, 14 spontaneous SPD8 revertants with a functional hprt gene were isolated and characterized using PCR and sequencing. The data revealed that although the SPD8 cell line arose by non-homologous recombination, it reverts spontaneously by homologous recombination. Interestingly, the downstream copy of exon 7 was restored by this process. This was indicated by the presence of a specific mutation, a T-to-G transversion, close to the breakpoint, a characteristic unique to the SPD8 clone. Our results suggest that the spontaneous reversion of this cell line by homologous recombination may involve an exchange, rather than a conversion mechanism.
authors.affiliation: Department of Genetic and Cellular Toxicology, Wallenberg Laboratory, Stockholm University, Stockholm, S-106 91, Sweden.
authors.forename: T
authors.initials: T
authors.lastname: Helleday
authors.forename: C
authors.initials: C
authors.lastname: Arnaudeau
authors.forename: D
authors.initials: D
authors.lastname: Jenssen
mesh_terms: D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D006224:Cricetinae; D005786:Gene Expression Regulation; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics*; D008969:Molecular Sequence Data; D005810:Multigene Family; D011995:Recombination, Genetic
chemical_list: D007041:Hypoxanthine Phosphoribosyltransferase