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Regulation of the bacterial cell cycle by an integrated genetic circuit


How bacteria regulate cell cycle progression at a molecular level is a fundamental but poorly understood problem. In Caulobacter crescentus, two-component signal transduction proteins are crucial for cell cycle regulation, but the connectivity of regulators involved has remained elusive and key factors are unidentified. Here we identify ChpT, an essential histidine phosphotransferase that controls the activity of CtrA, the master cell cycle regulator. We show that the essential histidine kinase CckA initiates two phosphorelays, each requiring ChpT, which lead to the phosphorylation and stabilization of CtrA. Downregulation of CckA activity therefore results in the dephosphorylation and degradation of CtrA, which in turn allow the initiation of DNA replication. Furthermore, we show that CtrA triggers its own destruction by promoting cell division and inducing synthesis of the essential regulator DivK, which feeds back to downregulate CckA immediately before S phase. Our results define a single integrated circuit whose components and connectivity can account for the cell cycle oscillations of CtrA in Caulobacter.

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We thank Y.S. Liu and K. Thorn for help with microscopy, and K. Thorn, A. Komeili, L. Garwin and A. Murray for discussions and/or comments on the manuscript. We acknowledge support from the Office of Science (BER), US Department of Energy (M.T.L.) and the US National Science Foundation (K.R.R.). Support was also provided in part by an NIH NIGMS Center of Excellence grant to Harvard University.

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Reprints and permissions information is available at The authors declare no competing financial interests.

Correspondence to Michael T. Laub.

Supplementary information

  1. Supplementary Notes

    This file contains Supplementary Notes 1–3, Supplementary Figures 1–12, and Supplemental Tables 1 and 3. Supplementary Table 2 is provided separately. (PDF 7624 kb)

  2. Supplemental Table 2

    This file contains microarray data from the paper. (XLS 612 kb)

  3. Supplementary Data

    This file contains the key genes and proteins used in this study. (DOC 19 kb)

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Figure 1: Identification and in vitro reconstitution of two phosphorelays controlling CtrA.
Figure 2: chpT encodes a histidine phosphotransferase that is essential for viability and phenocopies ctrAts and cckAts.
Figure 3: DivK˜P triggers the G1–S transition by causing inactivation and delocalization of CckA.
Figure 4: Schematic of cell cycle regulation in Caulobacter.


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