Home ＞GCOE Researchers ＞Takao KONDO

GCOE Researchers

Takao KONDO

Affiliation
/Position		 Graduate School of Science, Division of Biological Science, Professor
Doctorate Doctor of Science
Research interests Molecular mechanisms of the circadian clock system
address kondo＠bio.nagoya-u.ac.jp
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+81-52-789-2498
  Laboratory

Outline of research

The circadian clock is a fundamental intracellular apparatus to harmonize metabolism of living organisms to day/night alteration of the Earth. Many organisms (including humans) that live under a day-and-night cycle possess this system, which has been physiologically conserved over the course of evolution. I have studied the biological clock since I was a graduate student and the research on cyanobacterial circadian clock has been recognized as unique research originated in Japan. In the early 1990s, we initiated this project by screening and developing suitable experimental system. Recently, as shown in the figure, we discovered that a stable 24-hour oscillation can be generated by mixing only three Kai proteins and ATP in a test tube. Thus, we succeeded in reconstructing the circadian clock in vitro for the first time. This discovery can be said to be a Copernican Revolution in the study of circadian clocks.

We first monitored cyanobacterial gene expression in living cells using a bioluminescence reporter gene to automatically measure the circadian rhythm (PNAS 1993). Next, we developed an instrument to analyze the individual circadian clock behavior of 10,000 independent colonies on agar plates. Using this instrument, we isolated a number of circadian-clock mutants (Science, 1994), leading to the identification of a clock genes　cluster named kaiABC (named after the Japanese word kaiten, meaning “rotation”). We demonstrated that the expression of these genes is regulated by both positive and negative feedback controls, and proposed a transcription-translation oscillating model that explains the circadian oscillation as an autogenous regulation of the kaiC gene expression (Science, 1998). Next, we inquired why this oscillation has a period of 24 hours, and characterized the phosphorylation cycle of KaiC with biochemical analysis of the Kai proteins. Subsequently, we found that the phosphorylation cycle of KaiC continues even in darkness, where kaiC transcription is completely halted (Science, 2005). Based on these findings, we ultimately succeeded in reconstituting the clock in vitro, as mentioned above (Science, 2005). This discovery revealed a novel protein function: the generation of temporal information with a tiny amount of energy. We analyzed the mechanisms of this oscillation, and revealed the complex dynamics of Kai protein assembly (Mol. Cell, 2006) and phosphorylation program installed in KaiC. Furthermore, we showed that the ATPase activity of KaiC is stably regulated and determines the period of the circadian rhythm. Meanwhile, we demonstrated that the cyanobacterial circadian clock persisted independently of the cell division cycle (Science, 1997) and that expression of almost all genes are under the control of the circadian clock (Genes & Dev., 1995; PNAS, 2004).

References

  1. Kitayama, Y. et al. (2008) Dual KaiC-based oscillations constitute the circadian system of cyanobacteria, Genes Dev., 22：1513-1521
  2. Kondo, T. (2008) A cyanobacterial circadian clock based on the Kai oscillator In Clocks and Rhythms. Eds. Stillman, B. & Stewart, D., Cold Spring Harbor Laboratory press
  3. Ito, H. et al. (2007) Origin of the resilience of the cyanobacterial circadian clock. Nat. Struct. Mol. Biol., 14: 1084-1088
  4. Terauchi, K. et al. (2007) The ATPase activity of KaiC determines the basic timing for circadian clock of cyanobacteria. Proc. Natl. Acad. Sci. USA, 104: 16377-16381
  5. Nishiwaki, T. et al. (2007) A sequential program of dual phosphorylation of KaiC as a basis for circadian rhythm in cyanobacteria. EMBO J., 26: 4029-4037
  6. Kageyama T. et al. (2006) Cyanobacterial circadian pacemaker: Kai protein complex dynamics in the KaiC phosphorylation cycle in vitro. Mol. Cell, 23: 161-171
  7. Nakajima, M. et al. (2005) Reconstitution of circadian oscillation of cyanobacterial KaiC phosphorylation in vitro. Science, 308: 414-5
  8. Tomita, J. et al. (2005) No transcription-translation feedback in circadian rhythm of KaiC phosphorylation. Science, 307: 251-254
  9. Ishiura, M. et al. (1998) Expression of a gene cluster kaiABC as a circadian feedback process in cyanobacteria. Science, 281: 1519-1523
  10. Kondo, T. et al. (1994) Circadian clock mutants of cyanobacteria. Science, 266: 1233-1236

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