Dual KaiC-based oscillations constitute the circadian system of cyanobacteria
Dual KaiC-based oscillations constitute the circadian system of cyanobacteria
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DOI：
10.1101/gad.1661808
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发表时间：
2008-06-01
影响因子：
10.5
通讯作者：
Kondo, Takao
中科院分区：
文献类型：
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作者：
Kitayama, Yohko;Nishiwaki, Taeko;Kondo, Takao
在蓝细菌细长聚球藻PCC 7942中，KaiA、KaiB和KaiC蛋白对于昼夜节律的产生是必需的。在体内和体外，KaiC的磷酸化受KaiA的正调控，受KaiB的负调控，并显示出昼夜节律性。KaiC磷酸化的自主昼夜循环被认为是生物钟的基本起搏器，并控制蓝藻中全基因组的基因表达。在这项研究中，我们发现，即使KaiC因kaiA过表达而停滞在磷酸化状态，基因表达的温度补偿昼夜节律振荡也会持续存在。此外，两个磷酸化突变体表现出较长周期的转录振荡。在kaiA过表达和磷酸化缺陷型菌株中，KaiC振荡，磷酸化缺陷型KaiC的瞬时过表达重置了节律的相位。这些结果表明，在KaiC丰度的转录和抑制为基础的振荡也是重要的昼夜节律的产生在蓝藻。此外，在低温下，只有当KaiC磷酸化周期和转录和翻译周期都完整时，蓝藻才能表现出昼夜节律。我们的研究结果表明，基于KaiC的生化特性的多耦合振荡系统对于维持蓝藻中稳健和精确的昼夜节律是重要的。
In the cyanobacterium Synechococcus elongatus PCC 7942, the KaiA, KaiB, and KaiC proteins are essential for the generation of circadian rhythms. Both in vivo and in vitro, phosphorylation of KaiC is regulated positively by KaiA and negatively by KaiB and shows circadian rhythmicity. The autonomous circadian cycling of KaiC phosphorylation is thought to be the basic pacemaker of the circadian clock and to control genome-wide gene expression in cyanobacteria. In this study, we found that temperature-compensated circadian oscillations of gene expression persisted even when KaiC was arrested in the phosphorylated state due to kaiA overexpression. Moreover, two phosphorylation mutants showed transcriptional oscillation with a long period. In kaiA-overexpressing and phosphorylation-deficient strains, KaiC oscillated and transient overexpression of phosphorylation-deficient kaiC reset the phase of the rhythm. These results suggest that transcription- and translation-based oscillations in KaiC abundance are also important for circadian rhythm generation in cyanobacteria. Furthermore, at low temperature, cyanobacteria can show circadian rhythms only when both the KaiC phosphorylation cycle and the transcription and translation cycle are intact. Our findings indicate that multiple coupled oscillatory systems based on the biochemical properties of KaiC are important to maintain robust and precise circadian rhythms in cyanobacteria.