Covalent linkage between DNA and proteins produces highly toxic lesions and can be caused by commonly used chemotherapeutic agents, by internal and external chemicals and by radiation. In this study, using Escherichia coli, we investigate the consequences of 5-azacytidine (5-azaC), which traps covalent complexes between itself and the Dcm cytosine methyltransferase protein. DNA protein crosslink-dependent effects can be ascertained by effects that arise in wild-type but not in dcmΔ strains. We find that 5-azaC induces the bacterial DNA damage response and stimulates homologous recombination, a component of which is Dcm-dependent. Template-switching at an imperfect inverted repeat (“quasipalindrome”, QP) is strongly enhanced by 5-azaC and this enhancement was entirely Dcm-dependent and independent of double-strand break repair. The SOS response helps ameliorate the mutagenic effect of 5-azaC but this is not a result of SOS-induced DNA polymerases since their induction, especially PolIV, seems to stimulate QP-associated mutagenesis. Cell division regulator SulA was also required for recovery of QP mutants induced by 5-azaC. In the absence of Lon protease, Dcm-dependent QP-mutagenesis is strongly elevated, suggesting it may play a role in DPC tolerance. Deletions at short tandem repeats, which occur likewise by a replication template-switch, are elevated, but only modestly, by 5-azaC. We see evidence for Dcm-dependent and-independent killing by 5-azaC in sensitive mutants, such as recA, recB, and lon; homologous recombination and deletion mutations are also stimulated in part by a Dcm-independent effect of 5-azaC. Whether this occurs by a different protein/DNA crosslink or by an alternative form of DNA damage is unknown

DNA 和蛋白质之间的共价连接会产生剧毒损伤，并且可能由常用的化学治疗剂、内部和外部化学物质以及辐射引起。在这项研究中，我们使用大肠杆菌研究了 5-氮杂胞苷 (5-azaC) 的后果，它在自身和 Dcm 胞嘧啶甲基转移酶蛋白之间捕获共价复合物。DNA 蛋白交联依赖性效应可以通过在野生型中出现但在dcm中不出现的效应来确定Δ菌株。我们发现 5-azaC 诱导细菌 DNA 损伤反应并刺激同源重组，其中一个成分是 Dcm 依赖性的。5-azaC 强烈增强了不完美的反向重复（“quasipalindrome”，QP）的模板转换，这种增强完全依赖于 Dcm，与双链断裂修复无关。SOS 反应有助于改善 5-azaC 的诱变作用，但这不是 SOS 诱导的 DNA 聚合酶的结果，因为它们的诱导，尤其是 PolIV，似乎刺激了 QP 相关的诱变。恢复由 5-azaC 诱导的 QP 突变体也需要细胞分裂调节剂 SulA。在没有 Lon 蛋白酶的情况下，Dcm 依赖性 QP 诱变强烈升高，表明它可能在 DPC 耐受中起作用。短串联重复的缺失，同样通过复制模板转换发生的，5-azaC 升高，但仅适度升高。我们看到了敏感突变体中 5-azaC 对 Dcm 依赖性和非依赖性杀伤的证据，例如recA、recB和lon；同源重组和缺失突变也部分受到 5-azaC 的 Dcm 独立效应的刺激。这是由不同的蛋白质/DNA交联还是由另一种形式的DNA损伤引起的尚不清楚