BIOPHYSICAL THEORY AND MODELING |
A model for circadian rhythm of cyanobacteria, which maintains oscillation without gene expression
Gen Kurosawa 1*, Kazuyuki Aihara 2 and Yoh Iwasa 3
1 Aihara Complexity Modelling Project
2 The University of Tokyo
3 Kyushu University
* To whom correspondence should be addressed. E-mail: kurosawa{at}aihara.jst.go.jp.
Submitted on October 21, 2005
Revised on November 30, 2005
Accepted on 3 May 2006
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Abstract |
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An intriguing property of the cyanobacterial circadian clock is that endogenous rhythm persists when protein abundances are kept constant either in the presence of translation and transcription inhibitors or in the constant dark condition. Here we propose a regulatory mechanism of KaiC phosphorylation for the generation of circadian oscillations in cyanobacteria. In the model, clock proteins KaiA and KaiB are assumed to have multiple states, regulating the KaiC phosphorylation process. The model can explain (1) the sustained oscillation of gene expression and protein abundance when the expression of kaiBC gene is regulated by KaiC protein, and (2) the sustained oscillation of phosporylated KaiC when transcription and translation processes are inhibited and total protein abundance is fixed. Results of the present paper suggest that KaiA and KaiB strengthen the nonlinearity of KaiC phosphorylation, thereby promote the circadian rhythm in cyanobacteria.
Key Words:
KaiC, bifurcation, circadian rhythms, cyanobacteria, cycle without transcription-translation feedback, mathematical models
