A cyanobacteria internal clock based on the Kai protein cycle

The circadian oscillation of KaiC phosphorylation persisted for at least three cycles in vitro.

• KaiA, KaiB, and KaiC are essential components of the circadian clock in the cyanobacterium Synechococcus elongatus PCC 7942.
• The oscillation of KaiC phosphorylation is identified as the primary pacemaker of the cyanobacterial circadian clock.
• In vitro observations showed that period lengths of KaiC mutants were consistent with those measured in living organisms.
• Four aspects of the KaiC phosphorylation cycle were analyzed, including protein interactions and energetics influencing the circadian period.
• A circadian program consisting of KaiA, KaiB, and KaiC has been proposed to regulate biological time in cells.

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