Abstract
Cyanobacteria are the simplest organisms known to have a circadian clock. A circadian clock gene cluster kaiABC was cloned from the cyanobacterium Synechococcus elongatue PCC 7942 and a transcription/translation-based autoregulatory loop of kaiBC gene expression has been proposed to drive circadian rhythms. KaiA and KaiC were proposed as positive and negative regulators of kaiBC expression, respectively. In addition, KaiA-mediated activation of kaiBC expression was KaiC dependent, suggesting that KaiC also functions in a positive feedback process in the molecular oscillatory mechanism. However, we showed that self-sustainable oscillation of KaiC phosphorylation was reconstituted in vitro. Therefore, KaiC phosphorylation cycle is assumed to be a basic timing process of the circadian clock. In this study, we investigated cyanobacterial circadian oscillator in vitro and in vivo.
