Does the Kai clock rotate?

Jimin Wang (Yale University, New Haven, CT) suggests that an ancient circadian clock rotates much like a hand on an analogue clock. His analysis of cyanobacterial clock protein structures reveals a similarity with the F₁-ATPase rotary motor.

The cyanobacterial clock is controlled by the KaiA, KaiB, and KaiC proteins, which form a complex at night that falls apart in the day. Mutations causing more stable complexes correspond to a longer periodicity. But little is known about how the timing of complex formation is controlled. Wang analyzed the recently solved structures of the Kai proteins to suggest a mechanism.

When KaiC is ATP-bound, the Kai complex is stable. But when ATP is bumped off by autophosphorylation near the ATP-binding site, the complex falls apart. Autophosphorylation...