Abstract
Circadian rhythms are endogenous oscillations of physiological activities with a period of about 24 hours, which allow organisms to efficiently adapt to the day/night alteration of their environment. Cyanobacteria are the simplest organisms that exhibit circadian rhythms. Three genes, kaiA, kaiB and kaiC are essential components of circadian clock in the cyanobacterium Synechococcus elongatus PCC 7942. Phosphorylation dynamics of KaiC is modulated by KaiA and KaiB, and phosphorylation state of KaiC oscillates in the cells with a 24-hour period. Two amino acid residues on KaiC to which posphoryl groups attach were identified, showing that the phosphorylation residues are necessary for in-vivo oscillation. We have reconstituted the self-sustainable oscillation of KaiC phosphorylation in vitro with three recombinant Kai proteins and ATP. We are investigating the molecular mechanism of in-vitro KaiC phosphorylation cycle.
