KaiC

KaiC is a core component of the circadian clock in cyanobacteria. It is a highly conserved protein found in many prokaryotic organisms. KaiC is a hexameric ATPase that plays a central role in the temporal regulation of circadian gene expression.

The circadian clock in cyanobacteria is a sophisticated molecular oscillator that drives daily rhythms in cellular processes. The KaiABC system is the minimal core of this clock, consisting of three proteins: KaiA, KaiB, and KaiC. KaiA acts as a positive regulator, KaiB as a negative regulator, and KaiC as the central clockwork.

KaiC exists in two main states, active and inactive, which cycle over a 24-hour period. This cycling is driven by ATP hydrolysis and a complex series of post-translational modifications, including autophosphorylation and dephosphorylation. The phosphorylation state of KaiC is crucial for its interaction with KaiA and KaiB, thereby controlling the timing of the circadian cycle.

The precise mechanism of the KaiABC oscillator involves a feedback loop where the phosphorylation status of KaiC influences the activity of KaiA and KaiB, which in turn regulate KaiC's phosphorylation. This intricate interplay ensures the robust and self-sustaining nature of the circadian rhythm. The study of KaiC and the cyanobacterial circadian clock has provided valuable insights into the fundamental principles of biological timekeeping.