Component of the KaiABC clock protein complex, which constitutes the main circadian regulator in cyanobacteria. The KaiABC complex may act as a promoter-non-specific transcription regulator that represses transcription, possibly by acting on the state of chromosome compaction. In the complex, it decreases the phosphorylation status of KaiC. It has no effect on KaiC by itself, but instead needs the presence of both KaiA and KaiC, suggesting that it acts by antagonizing the interaction between KaiA and KaiC. Homodimer. Component of the KaiABC complex, at least composed of a KaiC homohexamer, a KaiB dimer and two KaiA dimers. The KaiABC complex also interacts with SasA. Belongs to the KaiB family.