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Proc Natl Acad Sci U S A. 2004 Jan 20;101(3):881-5. Epub 2004 Jan 6.

Global gene repression by KaiC as a master process of prokaryotic circadian system.

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  • 1Division of Biological Science, Graduate School of Science, Nagoya University, and Core Research for Evolutional Science and Technology, Japan Science and Technology Corporation, Furo-cho, Chikusa, Nagoya 464-8602, Japan.


A kaiABC clock gene cluster was previously identified from cyanobacterium Synechococcus elongatus PCC 7942, and the feedback regulation of kai genes was proposed as the core mechanism generating circadian oscillation. In this study, we confirmed that the Kai-based oscillator is the dominant circadian oscillator functioning in cyanobacteria. We probed the nature of this regulation and found that excess KaiC represses not only kaiBC but also the rhythmic components of all genes in the genome. This result strongly suggests that the KaiC protein primarily coordinates genomewide gene expression, including its own expression. We also found that a promoter derived from E. coli is feedback controlled by KaiC and restores the complete circadian rhythm in kaiBC-inactivated arrhythmic mutants, provided it can express kaiB and kaiC genes at an appropriate level. Unlike eukaryotic models, specific regulation of the kaiBC promoter is not essential for cyanobacterial circadian oscillations.

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