Cyanobacterial circadian clockwork:: roles of KaiA, KaiB and the kaiBC promoter in regulating KaiC
Cyanobacterial circadian clockwork:: roles of KaiA, KaiB and the kaiBC promoter in regulating KaiC
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DOI：
10.1093/emboj/cdg168
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发表时间：
2003-05-01
期刊：
影响因子：
11.4
通讯作者：
Johnson, CH
中科院分区：
文献类型：
--
作者：
Xu, Y;Mori, T;Johnson, CH
利用我们异位表达蓝藻时钟蛋白KaiC的模式菌株，我们发现真核生物的生物钟的一些特征在原核蓝藻的时钟中是保守的，而另一些则不是。一个意想不到的区别是，蓝藻中的昼夜自我调节反馈环不需要真核生物中特定的时钟基因启动子，因为异源启动子可以在功能上取代kaiBC启动子。另一方面，真核生物时钟蛋白与蓝藻KaiC蛋白的相似之处在于KaiC在体内被磷酸化。其他必需时钟蛋白KaiA和Kaib调节KaiC的磷酸化状态，KaiA抑制KaiC去磷酸化，Kaib拮抗KaiA的这一作用。根据对时钟突变的分析，我们得出结论：蓝藻的昼夜节律由KaiC的磷酸化状态决定，也由KaiC的降解速度决定。这些观察结果被整合到一个模型中，提出了染色体状态的节律变化。
Using model strains in which we ectopically express the cyanobacterial clock protein KaiC in cells from which the clock genes kaiA, kaiB and/or kaiC are deleted, we found that some features of circadian clocks in eukaryotic organisms are conserved in the clocks of prokaryotic cyanobacteria, but others are not. One unexpected difference is that the circadian autoregulatory feedback loop in cyanobacteria does not require specific clock gene promoters as it does in eukaryotes, because a heterologous promoter can functionally replace the kaiBC promoter. On the other hand, a similarity between eukaryotic clock proteins and the cyanobacterial KaiC protein is that KaiC is phosphorylated in vivo. The other essential clock proteins KaiA and KaiB modulate the status of KaiC phosphorylation; KaiA inhibits KaiC dephosphorylation and KaiB antagonizes this action of KaiA. Based upon an analysis of clock mutants, we conclude that the circadian period in cyanobacteria is determined by the phosphorylation status of KaiC and also by the degradation rate of KaiC. These observations are integrated into a model proposing rhythmic changes in chromosomal status.