The cyanobacterial clock proteins KaiA and KaiB are proposed as regulators of the circadian rhythm in cyanobacteria. The overall fold of the KaiA C-terminal domain is that of a four-helix bundle, which forms a dimer in the known structure [1].

1: Anabaena circadian clock proteins KaiA and KaiB reveal a potential common binding site to their partner KaiC. Garces RG, Wu N, Gillon W, Pai EF; EMBO J 2004;23:1688-1698. PMID:15071498

2: Crystal structure of circadian clock protein KaiA from Synechococcus elongatus. Ye S, Vakonakis I, Ioerger TR, LiWang AC, Sacchettini JC; J Biol Chem. 2004;279:20511-20518. PMID:15007067