Circadian clock KaiC, bacteria (IPR013503)
Short name: Circadian_KaiC_bact
Overlapping homologous superfamilies
- Circadian clock protein kinase KaiC (IPR030665)
- Circadian clock KaiC, bacteria (IPR013503)
The circadian clock protein KaiC, is encoded in the kaiABC operon that controls circadian rhythms and may be universal in Cyanobacteria. Each member contains two copies of the KaiC domain, which is also found in other proteins. KaiC performs autophosphorylation and acts as its own transcriptional repressor. Kai proteins (KaiA and KaiC) appear to positively and negatively regulate kaiBC transcription which is consistent with a transcription/translation oscillatory (TTO) feedback model, believed to be at the core of all self-sustained circadian timers. However, the cyanobacterial circadian clock is able to function without de novo synthesis of clock gene mRNAs and the clock proteins, and the period is accurately determined without TTO feedback and the system is also temperature-compensated. It has been demonstrated that these three purified proteins form a temperature-compensated molecular oscillator in vitro that exhibits rhythmic phosphorylation and dephosphorylation of KaiC[PMID: 16628225].
A negative-stain electron microscopy study of Synechococcus elongatus (Thermosynechococcus elongatus) and Thermosynechococcus elongatus BP-1 KaiA-KaiC complexes in combination with site-directed mutagenesis reveals that KaiA binds exclusively to the CII half of the KaiC hexamer. The EM-based model of the KaiA-KaiC complex reveals protein-protein interactions at two sites: the known interaction of the flexible C-terminal KaiC peptide with KaiA, and a second postulated interaction between the apical region of KaiA and the ATP binding cleft on KaiC. This model brings KaiA mutation sites that alter clock period or abolish rhythmicity into contact with KaiC and suggests how KaiA might regulate KaiC phosphorylation [PMID: 16628225].
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