Double strand breaks (DSBs) in E. coli chromosome (such as those induced by gamma rays) are repaired by recombination repair, during which a certain amount of DNA gets degraded. We monitored DNA degradation in gamma-irradiated cells to assess processing of DSBs. DNA degradation in irradiated cells is regulated by RecA protein concentration and its affinity of ssDNA binding, as well as by exonucleases that trim 3’-terminated ss tails. Here we determined the effects of proteins that affect formation and stability of RecA nucleofilaments on DNA degradation and cell survival. RecF and UvrD suppressed DNA degradation through RecA protein function and SOS induction, while also improving gamma survival. RecF and UvrD function in one pathway. Acting along with RecF, RecX suppressed DNA degradation and stimulated gamma-survival, which also depends on RecA protein and SOS induction. Furthermore, we determined a role in DNA degradation of several proteins that participate in DSB repair. RecN was required for DNA repair and for degradation suppression, acting on the RecBCD pathway. Furthermore, we show that SSB protein overproduction did not affect DNA degradation. Inactivation of RecG and RuvABC, proteins that catalyze the postsynaptic phase of recombination repair of DSBs, also did not affect DNA degradation, suggesting that once formed, recombination intermediates are not subject to DNA degradation, and that the postsynaptic phase is an irreversible, single-round process, unlike the presynaptic phase, which is mostly repetitive.

大肠杆菌中的双链断裂（DSB）通过重组修复来修复染色体（例如由伽马射线诱导的染色体），在此期间一定数量的DNA降解。我们监测了γ射线照射的细胞中的DNA降解，以评估DSB的加工。受辐照的细胞中的DNA降解受RecA蛋白浓度及其与ssDNA结合的亲和力以及修剪3'末端ss尾巴的外切核酸酶的调控。在这里，我们确定了影响RecA核丝形成和稳定性的蛋白质对DNA降解和细胞存活的影响。RecF和UvrD通过RecA蛋白功能和SOS诱导抑制了DNA降解，同时还提高了伽马存活率。RecF和UvrD在一种途径中起作用。与RecF一起起作用，RecX抑制DNA降解并刺激了伽马存活率，这也取决于RecA蛋白和SOS诱导。此外，我们确定了参与DSB修复的几种蛋白质在DNA降解中的作用。RecN是DNA修复和降解抑制所必需的，它作用于RecBCD途径。此外，我们表明SSB蛋白的过量生产不会影响DNA降解。RecG和RuvABC（催化DSB重组修复的突触后阶段的蛋白质）的失活也不会影响DNA降解，这表明重组中间体一旦形成，就不会发生DNA降解，并且突触后阶段是不可逆的单-整个过程，与突触前阶段不同，后者通常是重复的。我们表明SSB蛋白的过量生产不会影响DNA降解。RecG和RuvABC（催化DSB重组修复的突触后阶段的蛋白质）的失活也不会影响DNA降解，这表明重组中间体一旦形成，就不会发生DNA降解，并且突触后阶段是不可逆的单-整个过程，与突触前阶段不同，后者通常是重复的。我们表明SSB蛋白的过量生产不会影响DNA降解。RecG和RuvABC（催化DSB重组修复的突触后阶段的蛋白质）的失活也不会影响DNA降解，这表明重组中间体一旦形成，就不会发生DNA降解，并且突触后阶段是不可逆的单-整个过程，与突触前阶段不同，后者通常是重复的。