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. We show here that the temperature-compensated ATPase activity of KaiC oscillates in a circadian manner in vitro. KaiC showed very low ATPase activity (16 ATP day-1), which was stimulated and suppressed by KaiA and KaiB, respectively. The activities of KaiC mutant variants were directly proportional to their cycle frequencies, indicating that the ATPase activity defines the circadian oscillation period. The KaiC ATPase activity is the most elementary mechanism underlying circadian periodicity in cyanobacteria.
