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A cyanobacterial circadian clockwork
Carl Hirschie Johnson1, Tetsuya Mori, Yao Xu
1Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee, USA. carl.h.johnson@vanderbilt.edu
Current Biology : CB
|September 13, 2008
Summary
Cyanobacteria utilize a global circadian system involving a post-translational oscillator (PTO) and feedback loops. This system, with its core KaiA, KaiB, and KaiC proteins, explains key circadian rhythm characteristics.
Area of Science:
- Molecular Biology
- Chronobiology
- Biochemistry
Background:
- Cyanobacteria are a key model organism for studying circadian rhythms.
- Their circadian system globally regulates gene expression and chromosome topology.
- This temporal program enhances fitness in rhythmic environments.
Purpose of the Study:
- To elucidate the molecular mechanisms underlying cyanobacterial circadian rhythms.
- To explain the biochemical properties of the circadian oscillator, including its time constant, precision, and temperature compensation.
Main Methods:
- In vitro reconstitution of the post-translational oscillator (PTO) using purified KaiA, KaiB, and KaiC proteins and ATP.
- Crystallization and structural determination of the core oscillator proteins.
- Analysis of the interplay between the circadian pacemaker and the cell division cycle.
Main Results:
- The cyanobacterial circadian mechanism involves both a PTO and a transcriptional/translational feedback loop (TTFL).
- The PTO, composed of KaiA, KaiB, and KaiC, can be reconstituted in vitro and its core proteins structurally characterized.
- The circadian pacemaker is independent of the cell division cycle, potentially due to the persistent PTO.
Conclusions:
- Recent advances in biochemistry, biophysics, and structural biology are close to explaining the fundamental characteristics of the cyanobacterial circadian oscillator.
- The PTO plays a crucial role in the robustness and characteristics of the circadian clock.
- Understanding the cyanobacterial system provides insights into the universal principles of circadian rhythmicity.
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