ATPase activity of KaiC defines the basic timing for circadian oscillator in cyanobacterium Synechococcus elongatus PCC7942

Abstract

In cyanobacterium Syncehococcus elongatus PCC7942, self-sustainable oscillation of KaiC phosphorylation has been reconstituted in vitro, demonstrating that this cycle is the basic time generator of the circadian clock. The ATPase activity of KaiC satisfies the characteristics of the circadian oscillation, the period length, and the temperature compensation. KaiC possesses extremely weak but stable ATPase activity in vitro. Moreover, the activities of wild-type KaiC and period-mutant proteins are directly proportional to their in vivo circadian frequencies, indicating that the ATPase activity defines the circadian period. Thus, we attempt to demonstrate that the energy released upon ATP hydrolysis is stored in KaiC as structural tension which downregulates its own ATPase activity.