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. Author manuscript; available in PMC: 2009 Jun 8.
Published in final edited form as: Curr Opin Microbiol. 2008 Nov 10;11(6):541–546. doi: 10.1016/j.mib.2008.10.003

Figure 1. A model of the KaiC phosphorylation rhythm.

Figure 1

During a circadian cycle (represented by a circle), the phosphorylation states of KaiC proceed in an orderly manner. The relative timing of the peak for each phosphoform, based on published data [5,6], is shown by its position on the circle. KaiA stimulates KaiC phosphorylation by repeated association with KaiC. Starting from unphosphorylated KaiC (U); KaiC is first phosphorylated at T432 (T), which is further phosphorylated to the fully phosphorylated form (ST); T432 residue dephosphorylates from ST-KaiC first, resulting in KaiC phosphorylated only at S431 (S). KaiB preferentially binds S-KaiC, which forms a ternary complex with KaiA and, presumably, inactivates it and allows KaiC to return to the unphosphorylated state. The phosphorylation phase is represented in green and the dephosphorylation phase in red.