Fig. 1

Kai protein interactions in S. elongatus

The core clock components, KaiC peptides, assemble into a ring-shaped hexamer that acts as an ATPase as each subunit undergoes cycles of phosphorylation and dephosphorylation. During the day, KaiA subunits repeatedly bind to the KaiC hexamer promoting autophosphorylation of KaiC. In the evening, KaiB peptides bind the hyperphosphorylated KaiC hexamer. The bound KaiB peptides simultaneously sequester KaiA and prevent it from interacting with KaiC in a manner that would promote autophosphorylation of KaiC overnight. When KaiC is sufficiently dephosphorylated, it releases the KaiAB complex, which allows the cycle to begin again. In the figure, the day-night cycle is indicated by a change in background; dark gray indicates night. The phosphorylation state of KaiC is indicated by the number of bound phosphates shown as small circles. Created with BioRender.com.