Steiner W W, Kuempel P L
Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Colorado 80309, USA.
J Bacteriol. 1998 Dec;180(23):6269-75. doi: 10.1128/JB.180.23.6269-6275.1998.
Sister chromatid exchange (SCE) in Escherichia coli results in the formation of circular dimer chromosomes, which are converted back to monomers by a compensating exchange at the dif resolvase site. Recombination at dif is site specific and can be monitored by utilizing a density label assay that we recently described. To characterize factors affecting SCE frequency, we analyzed dimer resolution at the dif site in a variety of genetic backgrounds and conditions. Recombination at dif was increased by known hyperrecombinogenic mutations such as polA, dut, and uvrD. It was also increased by a fur mutation, which increased oxidative DNA damage. Recombination at dif was eliminated by a recA mutation, reflecting the role of RecA in SCE and virtually all homologous recombination in E. coli. Interestingly, recombination at dif was reduced to approximately half of the wild-type levels by single mutations in either recB or recF, and it was virtually eliminated when both mutations were present. This result demonstrates the importance of both RecBCD and RecF to chromosomal recombination events in wild-type cells.
大肠杆菌中的姐妹染色单体交换（SCE）会导致环状二聚体染色体的形成，这些二聚体染色体通过在 dif 位点的补偿性交换又会转变回单体。在 dif 位点的重组具有位点特异性，并且可以通过利用我们最近描述的密度标记测定法来进行监测。为了表征影响 SCE 频率的因素，我们在多种遗传背景和条件下分析了 dif 位点处的二聚体分解情况。已知的高重组突变（如 polA、dut 和 uvrD）会增加在 dif 位点的重组。一个 fur 突变也会增加重组，该突变会增加氧化性 DNA 损伤。recA 突变会消除在 dif 位点的重组，这反映了 RecA 在大肠杆菌的 SCE 和几乎所有同源重组中的作用。有趣的是，recB 或 recF 中的单个突变会使在 dif 位点的重组减少到野生型水平的大约一半，而当两个突变都存在时，重组几乎被消除。这一结果证明了 RecBCD 和 RecF 对野生型细胞中染色体重组事件的重要性。
