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Hda-mediated inactivation of the DnaA protein and dnaA gene autoregulation act in concert to ensure homeostatic maintenance of the Escherichia coli chromosome

¹ Department of Life Sciences and Chemistry, Roskilde University, Roskilde DK-4000, Denmark; ² Department of Cell and Molecular Biology, Uppsala University, Biomedical Centre, Uppsala SE-751 24, Sweden; ³ Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA

Initiation of DNA replication in Eschericia coli requires the ATP-bound form of the DnaA protein. The conversion of DnaA–ATP to DnaA–ADP is facilitated by a complex of DnaA, Hda (homologous to DnaA), and DNA-loaded -clamp proteins in a process termed RIDA (regulatory inactivation of DnaA). Hda-deficient cells initiate replication at each origin mainly once per cell cycle, and the rare reinitiation events never coincide with the end of the origin sequestration period. Therefore, RIDA is not the predominant mechanism to prevent immediate reinitiation from oriC. The cellular level of Hda correlated directly with dnaA gene expression such that Hda deficiency led to reduced dnaA gene expression, and overproduction of Hda led to DnaA overproduction. Hda-deficient cells were very sensitive to variations in the cellular level of DnaA, and DnaA overproduction led to uncontrolled initiation of replication from oriC, causing severe growth retardation or cell death. Based on these observations, we propose that both RIDA and dnaA gene autoregulation are required as homeostatic mechanisms to ensure that initiation of replication occurs at the same time relative to cell mass in each cell cycle.

[Keywords: Chromosome replication; dnaA gene expression; E. coli; Hda protein; RIDA]

Received January 11, 2006; revised version accepted May 19, 2006.

E-MAIL lobner{at}ruc.dk; FAX 45-4674-3011.

Article is online at http://www.genesdev.org/cgi/doi/10.1101/gad.379506

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