Replication forks must respond to changes in nutrient conditions, especially in bacterial cells. By investigating the single-molecule dynamics of replicative helicase DnaC, DNA primase DnaG, and lagging-strand polymerase DnaE in the model bacterium Bacillus subtilis, we show that proteins react differently to stress conditions in response to transient replication blocks due to DNA damage, to inhibition of the replicative polymerase, or to downshift of serine availability. DnaG appears to be recruited to the forks by a diffusion and capture mechanism, becomes more statically associated after the arrest of polymerase, but binds less frequently after fork blocks due to DNA damage or to nutritional downshift. These results indicate that binding of the alarmone (p)ppGpp due to stringent response prevents DnaG from binding to forks rather than blocking bound primase. Dissimilar behavior of DnaG and DnaE suggests that both proteins are recruited independently to the forks rather than jointly. Turnover of all three proteins was increased during replication block after nutritional downshift, different from the situation due to DNA damage or polymerase inhibition, showing high plasticity of forks in response to different stress conditions. Forks persisted during all stress conditions, apparently ensuring rapid return to replication extension.

中文翻译：

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营养下调或化学诱导复制后细菌复制叉的单分子动力学

复制叉必须对营养条件的变化做出反应，尤其是在细菌细胞中。通过研究模型细菌枯草芽孢杆菌中复制解旋酶 DnaC、DNA 引物酶 DnaG 和滞后链聚合酶 DnaE 的单分子动力学，我们表明蛋白质对压力条件的反应不同，以响应 DNA 损伤引起的瞬时复制块、复制聚合酶的抑制或丝氨酸可用性的下降。DnaG 似乎通过扩散和捕获机制被招募到叉上，在聚合酶停滞后变得更加静态相关，但在由于 DNA 损伤或营养下降导致叉阻塞后结合的频率降低。这些结果表明，由于严格响应而引起的 alarmone (p)ppGpp 的结合阻止了 DnaG 与叉结合，而不是阻止结合的引发酶。DnaG 和 DnaE 的不同行为表明这两种蛋白质都是独立地而不是联合地被招募到叉子上的。在营养下降后的复制阻断期间，所有三种蛋白质的周转率都增加了，与由于 DNA 损伤或聚合酶抑制导致的情况不同，叉对不同压力条件的反应具有高度的可塑性。分叉在所有压力条件下都持续存在，显然确保了复制扩展的快速恢复。