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Nat Struct Mol Biol. 2007 Nov;14(11):1084-8. Epub 2007 Oct 28.

Autonomous synchronization of the circadian KaiC phosphorylation rhythm.

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Division of Biological Science, Graduate School of Science, Nagoya University, and Solution Oriented Research for Science and Technology (SORST) Program, Japan Science and Technology Agency (JST), Furo-cho 1, Chikusa-ku, Nagoya 464-8602, Japan.


The cyanobacterial circadian oscillator can be reconstituted in vitro by mixing three purified clock proteins, KaiA, KaiB and KaiC, with ATP. The KaiC phosphorylation rhythm persists for at least 10 days without damping. By mixing oscillatory samples that have different phases and analyzing the dynamics of their phase relationships, we found that the robustness of the KaiC phosphorylation rhythm arises from the rapid synchronization of the phosphorylation state and reaction direction (phosphorylation or dephosphorylation) of KaiC proteins. We further demonstrate that synchronization is tightly linked with KaiC dephosphorylation and is mediated by monomer exchange between KaiC hexamers during the early dephosphorylation phase. This autonomous synchronization mechanism is probably the basis for the resilience of the cyanobacterial circadian system against quantitative fluctuations in clock components during cellular events such as cell growth and division.

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