KaiA helps activate KaiC to keep the biological clock running in cyanobacteria

Activation of kaiBC expression by kaiA requires KaiC, indicating a positive feedback mechanism in the cyanobacterial circadian clock.

• KaiA is identified as a positive regulator of kaiBC expression.
• KaiC acts as a negative regulator in this autoregulatory system.
• Robust circadian phosphorylation of KaiC was observed.
• KaiA is essential for both in vivo phosphorylation of KaiC and in vitro autophosphorylation of KaiC.
• A long period mutation in kaiA2 attenuated the effects of KaiA on KaiC phosphorylation.
• A previously undocumented mutation in kaiC suppressed the long period phenotype and abnormal phosphorylation in the kaiA2 mutant.

Simplified