West S C, Countryman J K, Howard-Flanders P
Cell. 1983 Mar;32(3):817-29. doi: 10.1016/0092-8674(83)90068-5.
A key intermediate in general genetic recombination is a structure in which two double-stranded DNA molecules are covalently linked by a single-strand crossover characteristic of a Holliday junction. When the DNA molecules are circular, the recombinant structures take the form of a figure eight. We have used purified E. coli enzymes to construct biparental figure-eight DNA molecules in vitro from the DNA of two partially homologous plasmids. When purified figure-eight structures are transfected into recA- E. coli cells, they are resolved to produce monomeric or dimeric plasmid progeny, apparently by the cutting and joining of the Holliday crossover. The maturation of figure-eight molecules in bacteria is characterized by the formation and recovery of both parental and recombinant types, cross-over at a frequency of up to 50% and the capability for mismatch repair at regions of hybrid DNA. In these three regards, the products of figure-eight maturation resemble recombinant chromosomes formed at meiosis. These observations show that biparental figure eights behave as recombination intermediates that can be resolved into mature recombinants without need for a functional recA+ gene product.
一般遗传重组中的一个关键中间体是一种结构，其中两个双链DNA分子通过霍利迪连接体的单链交叉共价连接。当DNA分子是环状时，重组结构呈数字8的形式。我们已经使用纯化的大肠杆菌酶在体外从两个部分同源质粒的DNA构建双亲数字8 DNA分子。当将纯化的数字8结构转染到recA-大肠杆菌细胞中时，它们显然通过霍利迪交叉的切割和连接被分解以产生单体或二聚体质粒后代。细菌中数字8分子的成熟特征在于亲本类型和重组类型的形成与恢复、交叉频率高达50%以及在杂交DNA区域进行错配修复的能力。在这三个方面，数字8成熟的产物类似于减数分裂时形成的重组染色体。这些观察结果表明，双亲数字8作为重组中间体，无需功能性recA+基因产物即可分解为成熟的重组体。
