May be involved in signal transduction. Participates in the KaiABC clock protein complex, which constitutes the main circadian regulator in cyanobacteria, via its interaction with KaiC. Required for robustness of the circadian rhythm of gene expression and is involved in clock outputs. Interacts with KaiC. Participates in the KaiABC complex, whose core is composed of a KaiC homohexamer, a KaiB dimer and two KaiA dimers.