Two KaiA‐binding domains of cyanobacterial circadian clock protein KaiC

kaiABC, a gene cluster, encodes KaiA, KaiB and KaiC proteins that are essential to circadian rhythms in the unicellular cyanobacterium Synechococcus sp. strain PCC 7942. Kai proteins can interact with each other in all possible combinations. This study identified two KaiA-binding domains (C(KABD1) and C(KABD2)) in KaiC at corresponding regions of its duplicated structure. Clock mutations on the two domains and kaiA altered the strength of C(KABD)-KaiA interactions assayed by the yeast two-hybrid system. Thus, interaction between KaiA and KaiC through C(KABD1) and C(KABD2) is likely important for circadian timing in the cyanobacterium.