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Research Center of Integrative Molecular Systems Akiyama Group

Location: Myoudaiji, South Laboratory Bldg. Room313
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Circadian Clock, Cyanobacteria, Temperature Compensation

Origins of 24 Hour Period in Cyanobacterial Clock System

Circadian (approximately 24 h) clocks are endogenous time-keeping systems encapsulated in living cells, enabling organisms to adapt to daily fluctuation of exogenous environments on the Ear th.These time-keeping systems, found ubiquitously from prokaryotes to eukaryotes, share the three characteristics. First, the circadian rhythmicity of the clocks persists even without any external cues (self-sustainability). Second, the period is little dependent on ambient temperature (temperature compensation). Third, the phase of the clock can be reset by external stimuli such as lightning, humidity, or temperature so as to be synchronized to the external phase (synchronization).

KaiC, a core protein of the circadian clock in cyanobacteria, undergoes rhythmic structural changes over approximately 24 h in the presence of KaiA and KaiB (Kai oscillator). This slow dynamics spanning a wide range of both temporal and spatial scales is not well understood, and is central to a fundamental question: What determines the temperature-compensated 24 h period?1) The Kai oscillator reconstitutable in vitro is advantageous for studying its dynamic structure through a complementary usage of both X-ray crystallography2) and solution scattering3)-5), its transient response and synchronization by using physicochemical techniques4), and its molecular motion through a collaborative work with computational groups2). Our mission is to explore the frontier in molecular science of the cyanobacterial circadian clock from many perspectives6).  


Towards a Unified View of Temperature-compensated 24 h Period in Biological Clock System.

Selected Publications

  1. S. Akiyama, “Structural and dynamic aspects of protein clocks: How can they be so slow and stable?” CMLS 69, 2147-2160 (2012).
  2. J. Abe et al., “Atomic-scale Origins of Slowness in the Cyanobacterial Circadian Clock” Science 349, 312-316 (2015).
  3. S. Akiyama et al., “Assembly and Disassembly Dynamics of the Cyanobacterial Periodosome” Mol. Cell 29, 703-716 (2008).
  4. Y. Murayama et al., “Tracking and Visualizing the Circadian Ticking of the Cyanobacterial Clock Protein KaiC in Solution” EMBO J30, 68-78 (2011).
  5. Mukaiyama et al., Sci. Rep.8, 8803 (2018)
  6. 秋山 修志, ”時間生物学と放射光科学の接点”,放射光 (2016).