Dutreix M, Rao B J, Radding C M
Department of Human Genetics and Molecular Biophysics, Yale University School of Medicine, New Haven CT 06510.
J Mol Biol. 1991 Jun 20;219(4):645-54. doi: 10.1016/0022-2836(91)90661-o.
Since the ends of DNA chains are thought to be important in homologous recombination, the way in which RecA protein and similar recombination enzymes process ends is important. We analyzed the effects of ends both on the formation of joints, and the progression of strand exchange. When the only homologous end was provided by a single strand, there was no significant difference between the formation of joints at a 5' end or a 3' end; but in agreement with the report of Konforti & Davis, Escherichia coli single-stranded DNA binding protein (SSB) selectively inhibited the activity of 5' ends. Complete strand exchange, assessed by study of linear single-stranded and double-stranded substrates, took place only in the 5' to 3' direction relative to DNA in the nucleoprotein filament. These observations pose a paradox: in the presence of SSB, of which there are about 800 tetramers per cell, the formation of homologous joints by RecA protein is favored at a 3' end, from which, however, authentic strand exchange appears not to occur. Since observations reported here and elsewhere show that joints have different properties when formed at a 5' versus a 3' end, we suggest that they may be processed differently in vivo.
由于DNA链的末端被认为在同源重组中很重要，所以RecA蛋白及类似的重组酶处理末端的方式就很关键。我们分析了末端对连接形成以及链交换进程的影响。当唯一的同源末端由一条单链提供时，5'端或3'端连接形成之间没有显著差异；但与Konforti和Davis的报告一致，大肠杆菌单链DNA结合蛋白（SSB）选择性地抑制5'端的活性。通过研究线性单链和双链底物评估的完全链交换，仅在相对于核蛋白丝中的DNA从5'到3'的方向上发生。这些观察结果产生了一个悖论：在每个细胞约有800个四聚体的SSB存在的情况下，RecA蛋白在3'端有利于同源连接的形成，然而，真正的链交换似乎不会从3'端发生。由于此处和其他地方报道的观察结果表明，在5'端与3'端形成时连接具有不同的特性，我们认为它们在体内可能会被不同地处理。
