Initiation of DNA replication in Escherichia coli is coupled to cell size via the DnaA protein, whose activity is dependent on its nucleotide-bound state. However, the oscillations in DnaA activity have never been observed at the single-cell level. By measuring the volume-specific production rate of a reporter protein under control of a DnaA-regulated promoter, we could distinguish two distinct cell-cycle oscillators. The first, driven by both DnaA activity and SeqA repression, shows a causal relationship with cell size and divisions, similarly to initiation events. The second one, a reporter of DnaA activity alone, loses the synchrony and causality properties. Our results show that transient inhibition of gene expression by SeqA keeps the oscillation of volume-sensing DnaA activity in phase with the subsequent division event and suggest that DnaA activity peaks do not correspond directly to initiation events.

中文翻译：

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直接单细胞观察关键的大肠杆菌细胞周期振荡器


DNA复制的起始大肠杆菌通过 DnaA 蛋白与细胞大小耦合，其活性取决于其核苷酸结合状态。然而，从未在单细胞水平上观察到 DnaA 活性的振荡。通过测量受 DnaA 调节的启动子控制的报告蛋白的体积特异性生产率，我们可以区分两种不同的细胞周期振荡器。第一个由 DnaA 活性和 SeqA 抑制驱动，显示出与细胞大小和分裂的因果关系，类似于起始事件。第二个是单独的 DnaA 活动报告者，失去了同步性和因果关系特性。我们的结果表明，SeqA 对基因表达的瞬时抑制使体积感应 DnaA 活性的振荡与随后的分裂事件保持同步，并表明 DnaA 活性峰值并不直接对应于起始事件。