RNA‐DNA hybrids form throughout the chromosome during normal growth and under stress conditions. When left unresolved, RNA‐DNA hybrids can slow replication fork progression, cause DNA breaks, and increase mutagenesis. To remove hybrids, all organisms use ribonuclease H (RNase H) to specifically degrade the RNA portion. Here we show that, in addition to chromosomally encoded RNase HII and RNase HIII, Bacillus subtilis NCIB 3610 encodes a previously uncharacterized RNase HI protein, RnhP, on the endogenous plasmid pBS32. Like other RNase HI enzymes, RnhP incises Okazaki fragments, ribopatches, and a complementary RNA‐DNA hybrid. We show that while chromosomally encoded RNase HIII is required for pBS32 hyper‐replication, RnhP compensates for the loss of RNase HIII activity on the chromosome. Consequently, loss of RnhP and RNase HIII impairs bacterial growth. We show that the decreased growth rate can be explained by laggard replication fork progression near the terminus region of the right replichore, resulting in SOS induction and inhibition of cell division. We conclude that all three functional RNase H enzymes are present in B. subtilis NCIB 3610 and that the plasmid‐encoded RNase HI contributes to chromosome stability, while the chromosomally encoded RNase HIII is important for chromosome stability and plasmid hyper‐replication.

中文翻译：

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RnhP 是一种质粒携带的 RNase HI，有助于在祖先菌株枯草芽孢杆菌 NCIB 3610 中维持基因组

在正常生长和应激条件下，整个染色体形成 RNA-DNA 杂交体。如果不解决，RNA-DNA 杂交会减慢复制叉的进程，导致 DNA 断裂，并增加诱变。为了去除杂交体，所有生物都使用核糖核酸酶 H (RNase H) 来特异性降解 RNA 部分。在这里我们表明，除了染色体编码的 RNase HII 和 RNase HIII，枯草芽孢杆菌NCIB 3610 在内源性质粒 pBS32 上编码以前未表征的 RNase HI 蛋白 RnhP。与其他 RNase HI 酶一样，RnhP 切割冈崎片段、核糖块和互补的 RNA-DNA 杂交体。我们表明，虽然 pBS32 过度复制需要染色体编码的 RNase HIII，但 RnhP 补偿了染色体上 RNase HIII 活性的丧失。因此，RnhP 和 RNase HIII 的缺失会损害细菌的生长。我们表明，生长速率的降低可以通过右侧复制体末端区域附近的滞后复制叉进展来解释，导致 SOS 诱导和细胞分裂抑制。我们得出结论，所有三种功能性 RNase H 酶都存在于枯草芽孢杆菌中 NCIB 3610 和质粒编码的 RNase HI 有助于染色体稳定性，而染色体编码的 RNase HIII 对染色体稳定性和质粒超复制很重要。