The Kai oscillator

Abstract

Reconstitution of a circadian oscillator in a test tube marked an epoch in the field of chronobiology. Combining the three clock proteins (KaiA, KaiB, KaiC) with ATP is sufficient to generate a robust circadian rhythm. ATP hydrolysis by KaiC, phosphorylation/dephosphorylation of KaiC, and interactions among the Kai proteins can be observed using this oscillatory system. The ATPase activity of KaiC is the foundation of the system, functioning to determine the period length and underlying its temperature independence. An ordered cycle of phosphorylation and dephosphor-ylation reactions in the KaiC protein, as well as a dynamic protein-protein interaction profile mediated by the changes in the KaiC phosphorylation status, create the robust oscillation. Importantly, the Kai oscillator is likely to work in cyanobacterial cells to synchronize various cellular activities to an approximate daily cycle.