Circadian clock protein KaiA (IPR011648)

Short name: Circadian_clock_KaiA

Overlapping homologous superfamilies


Family relationships



KaiA is a component of the kaiABC clock protein complex, which constitutes the main circadian regulator in cyanobacteria. The kaiABC complex may act as a promoter-nonspecific transcription regulator that represses transcription, possibly by acting on the state of chromosome compaction. In the complex, KaiA enhances the phosphorylation status of kaiC. In contrast, the presence of kaiB in the complex decreases the phosphorylation status of kaiC, suggesting that kaiB acts by antagonising the interaction between kaiA and kaiC. The activity of KaiA activates kaiBC expression, while KaiC represses it. The overall fold of the KaiA monomer is that of a four-helix bundle, which forms a dimer in the known structure [PMID: 15071498]. KaiA functions as a homodimer. Each monomer is composed of three functional domains: the N-terminal amplitude-amplifier domain, the central period-adjuster domain and the C-termianl clock-oscillator domain. The N-terminal domain of KaiA, from cyanobacteria, acts as a psuedo-receiver domain, but lacks the conserved aspartyl residue required for phosphotransfer in response regulators [PMID: 12438647]. The C-terminal domain is responsible for dimer formation, binding to KaiC, enhancing KaiC phosphorylation and generating the circadian oscillations [PMID: 15170179]. The KaiA protein from Anabaena sp. (strain PCC 7120) lacks the N-terminal CheY-like domain.

GO terms

Biological Process

GO:0007623 circadian rhythm
GO:0006468 protein phosphorylation

Molecular Function

No terms assigned in this category.

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.