Abstract
Recently, we demonstrated that the central oscillator of cyanobacterial circadian clock was KaiC phosphorylation cycle. Moreover, we could reconstitute circadian oscillation of KaiC phosphorylation in vitro with three Kai proteins and ATP. Hence, the mechanism of the generation of the KaiC phosphorylation rhythm can be elucidated by biochemical analysis of three Kai proteins. In cyanobacterial cells, the accumulation levels of KaiC and KaiB show circadian rhythm, while level of KaiA is constant. When the amount of KaiA was altered, the period and amplitude of the in vitro KaiC phosphorylation rhythm were both changed. On the other hand, the period and the amplitude did not depend on the amount of KaiB, though indispensable for the generation of the KaiC phosphorylation rhythm. These results imply the stability of KaiC phosphorylation rhythm in vivo and the role of KaiA and KaiB in the generation of the KaiC phosphorylation rhythm.
