Yang D, Waldman A S
Department of Biological Sciences, University of South Carolina, Columbia 29208, USA.
Mol Cell Biol. 1997 Jul;17(7):3614-28. doi: 10.1128/MCB.17.7.3614.
Mouse Ltk- cell lines that contained a herpes simplex virus type 1 (HSV-1) thymidine kinase (tk) gene with a 16-bp insertion mutation linked to either a defective HSV-2 tk gene or a hybrid tk sequence comprised of HSV-1 and HSV-2 tk sequences were constructed. HSV-1 and HSV-2 tk genes have 81% nucleotide identity and hence are homeologous. Correction of the insertion mutant HSV-1 tk gene via recombination with the hybrid tk sequence required an exchange between homeologous tk sequences, although recombination could initiate within a region of significant sequence identity. Seven cell lines containing linked HSV-1 and HSV-1-HSV-2 hybrid tk sequences gave rise to tk+ segregants at an average rate of 10(-8) events per cell division. DNA sequencing revealed that each recombinant from these lines displayed an apparent gene conversion which involved an accurate transfer of an uninterrupted block of information between homeologous tk sequences. Conversion tract lengths ranged from 35 to >330 bp. In contrast, cell lines containing linked HSV-1 and HSV-2 tk sequences with no significant stretches of sequence identity had an overall rate of homeologous recombination of <10(-9). One such cell line produced homeologous recombinants at a rate of 10(-8). Strikingly, all homeologous recombinants from this latter cell line were due to crossovers between the HSV-1 and HSV-2 tk genes. Our results, which provide the first detailed analysis of homeologous recombination within a mammalian genome, suggest that rearrangements in mammalian genomes are regulated by the degree of sequence divergence located at the site of recombination initiation.
构建了含有单纯疱疹病毒1型（HSV-1）胸苷激酶（tk）基因的小鼠Ltk-细胞系，该基因带有一个16bp的插入突变，该突变与一个有缺陷的HSV-2 tk基因或一个由HSV-1和HSV-2 tk序列组成的杂交tk序列相连。HSV-1和HSV-2 tk基因有81%的核苷酸同一性，因此是同源的。通过与杂交tk序列重组来校正插入突变的HSV-1 tk基因需要在同源tk序列之间进行交换，尽管重组可以在一个具有显著序列同一性的区域内起始。七个含有相连的HSV-1和HSV-1-HSV-2杂交tk序列的细胞系产生tk+分离株的平均频率为每细胞分裂10(-8)次事件。DNA测序显示，来自这些细胞系的每个重组体都表现出明显的基因转换，这涉及到在同源tk序列之间准确转移一段不间断的信息。转换片段长度范围从35到>330bp。相比之下，含有相连的HSV-1和HSV-2 tk序列且没有显著序列同一性延伸的细胞系，其同源重组的总体频率<10(-9)。其中一个这样的细胞系产生同源重组体的频率为10(-8)。令人惊讶的是，来自后一个细胞系的所有同源重组体都是由于HSV-1和HSV-2 tk基因之间的交换。我们的结果首次对哺乳动物基因组内的同源重组进行了详细分析，表明哺乳动物基因组中的重排受重组起始位点处序列分歧程度的调控。
