Department of Biology, University of Copenhagen, Copenhagen, Denmark.
Mol Microbiol. 2020 Dec;114(6):906-919. doi: 10.1111/mmi.14531. Epub 2020 Jun 15.
Initiation of Escherichia coli chromosome replication is controlled by the DnaA initiator protein. Both rifampicin-mediated inhibition of transcription and ppGpp-induced changes in global transcription stops replication at the level of initiation. Here, we show that continued DnaA protein synthesis allows for replication initiation both during the rifampicin treatment and during the stringent response when the ppGpp level is high. A reduction in or cessation of de novo DnaA synthesis, therefore, causes the initiation arrest in both cases. In accordance with this, inhibition of translation with chloramphenicol also stops initiations. The initiation arrest caused by rifampicin was faster than that caused by chloramphenicol, despite of the latter inhibiting DnaA accumulation immediately. During chloramphenicol treatment transcription is still ongoing and we suggest that transcriptional events in or near the origin, that is, transcriptional activation, can allow for a few extra initiations when DnaA becomes limiting. We suggest, for both rifampicin treated cells and for cells accumulating ppGpp, that a turn-off of initiation from oriC requires a stop in de novo DnaA synthesis and that an additional lack of transcriptional activation enhances this process, that is, leads to a faster initiation stop.
大肠杆菌染色体复制的起始受 DnaA 起始蛋白控制。利福平介导的转录抑制和 ppGpp 诱导的全局转录变化都能在起始水平停止复制。在这里，我们表明，在利福平处理期间和 ppGpp 水平较高的严格反应期间，持续的 DnaA 蛋白合成允许进行复制起始。因此，减少或停止从头合成 DnaA 会导致两种情况下的起始停滞。与这一结果一致，用氯霉素抑制翻译也会阻止起始。尽管氯霉素立即抑制 DnaA 积累，但利福平引起的起始停滞比氯霉素引起的更快。在氯霉素处理期间，转录仍在继续进行，我们认为，在 ori 处或附近的转录事件，即转录激活，可以在 DnaA 变得有限时允许进行几次额外的起始。我们认为，对于利福平处理的细胞和积累 ppGpp 的细胞，oriC 处起始的关闭需要从头合成 DnaA 的停止，并且额外缺乏转录激活会增强这一过程，即导致更快的起始停止。
