Abstract
KaiC phosphorylation oscillation is the pacemaker of the cyanobacterial circadian clock. We recently demonstrated a self-sustainable robust circadian oscillation of KaiC phosphorylation by reconstituting KaiA, KaiB and KaiC proteins with ATP in vitro. A sequential program of phosphorylation of KaiC on two sites, S431 and T432, has been characterized and found that the phosphorylation state of each of these two residues regulates the phosphorylation /dephosphorylation of the other. The temperature-compensated ATPase activity of KaiC oscillates in a circadian manner in vitro. The activities of KaiC mutant variants without KaiA and KaiB were directly proportional to their cycle frequencies, indicating that the ATPase activity defines the circadian oscillation period. The mechanism of circadian clock is intrinsic to KaiC itself and at least three enzymatic activities, ATPase, kinase, and phosphatase, of KaiC mutually influence each other. Recent biochemical analysis of KaiC will be presented.
