Circadian rhythms in the synthesis and degradation of a master clock protein KaiC in cyanobacteria
Circadian rhythms in the synthesis and degradation of a master clock protein KaiC in cyanobacteria
复制标题
DOI：
10.1074/jbc.m405861200
复制
发表时间：
2004-08-27
影响因子：
4.8
通讯作者：
Iwasaki, H
中科院分区：
文献类型：
--
作者：
Imai, K;Nishiwaki, T;Iwasaki, H
核心时钟蛋白KaiC积累的昼夜节律已经被提出对于在连续光照条件下蓝细菌细长聚球藻PCC 7942中适当的昼夜节律定时是重要的。KaiC蛋白质丰度的循环延迟到其mRNA的节律，延迟了类似于8小时，这与KaiC作为kaiBC转录的负反馈调节剂的功能一致。在这里，我们提出了时间配置文件的合成和降解KaiC蛋白，确定其积累的节奏。KaiC的合成速率表现出强烈的昼夜节律振荡，其略微延迟mRNA的节律，并提前KaiC积累的节律约6 h。KaiC蛋白的稳定性也显示出昼夜节律的波动，使得KaiC降解在主观午夜期间受到抑制。这些结果表明，转录，翻译和翻译后过程是重要的适当的昼夜变化KaiC积累。此外，KaiC的磷酸化和非磷酸化形式的周转显示出强大的昼夜节律，彼此具有反相关系。有趣的是，当翻译被抑制时，KaiC降解和磷酸化在至少4小时内以昼夜节律相依赖的方式进行。因此，即使蛋白质合成发生任何扰动，昼夜节律的时间似乎也是灵活的。
A circadian rhythm in the accumulation of the core clock protein KaiC has been proposed to be important for proper circadian timing in the cyanobacterium Synechococcus elongatus PCC 7942 under continuous light conditions. Cycling in the abundance of the KaiC protein is delayed to the rhythm of its mRNA by similar to8 h, consistent with the proposed function of KaiC as a negative feedback regulator of kaiBC transcription. Here, we present temporal profiles of the synthesis and degradation of KaiC protein that determine the rhythm of its accumulation. The rate of KaiC synthesis shows a robust circadian oscillation, which is delayed to the mRNA rhythm slightly and advances the rhythm of KaiC accumulation by similar to6 h. The stability of KaiC protein also shows circadian fluctuations, such that KaiC degradation is suppressed during the mid-subjective night. These results suggest that transcriptional, translational, and posttranslational processes are important for the proper circadian changes in KaiC accumulation. Moreover, the turnovers of the phosphorylated and non-phosphorylated forms of KaiC show robust circadian rhythms with an anti-phase relationship to each other. Interestingly, when translation was inhibited, KaiC degradation and phosphorylation proceeded within at least 4 h in a circadian phase-dependent manner. Thus, the circadian timing seems flexible even when any perturbation in protein synthesis occurs.