KaiB functions as an attenuator of KaiC phosphorylation in the cyanobacterial circadian clock system

EMBO J. 2003 May 1;22(9):2127-34. doi: 10.1093/emboj/cdg212.


In the cyanobacterium Synechococcus elongatus PCC 7942, the KaiA, KaiB and KaiC proteins are essential for generation of circadian rhythms. We quantitatively analyzed the intracellular dynamics of these proteins and found a circadian rhythm in the membrane/cytosolic localization of KaiB, such that KaiB interacts with a KaiA-KaiC complex during the late subjective night. KaiB-KaiC binding is accompanied by a dramatic reduction in KaiC phosphorylation and followed by dissociation of the clock protein complex(es). KaiB attenuated KaiA-enhanced phosphorylation both in vitro and in vivo. Based on these results, we propose a novel role for KaiB in a regulatory link among subcellular localization, protein-protein interactions and post-translational modification of Kai proteins in the cyanobacterial clock system.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / metabolism
  • Bacterial Proteins / physiology*
  • Circadian Rhythm / physiology*
  • Circadian Rhythm Signaling Peptides and Proteins
  • Cyanobacteria / metabolism
  • Cyanobacteria / physiology*
  • Phosphorylation


  • Bacterial Proteins
  • Circadian Rhythm Signaling Peptides and Proteins
  • KaiB protein, cyanobacteria
  • KaiC protein, cyanobacteria