Expression of a Gene Cluster kaiABC as a Circadian Feedback Process in Cyanobacteria

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Science  04 Sep 1998:
Vol. 281, Issue 5382, pp. 1519-1523
DOI: 10.1126/science.281.5382.1519

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Cyanobacteria are the simplest organisms known to have a circadian clock. A circadian clock gene cluster kaiABC was cloned from the cyanobacterium Synechococcus. Nineteen clock mutations were mapped to the three kai genes. Promoter activities upstream of the kaiA and kaiB genes showed circadian rhythms of expression, and both kaiA andkaiBC messenger RNAs displayed circadian cycling. Inactivation of any single kai gene abolished these rhythms and reduced kaiBC-promoter activity. ContinuouskaiC overexpression repressed the kaiBCpromoter, whereas kaiA overexpression enhanced it. TemporalkaiC overexpression reset the phase of the rhythms. Thus, a negative feedback control of kaiC expression by KaiC generates a circadian oscillation in cyanobacteria, and KaiA sustains the oscillation by enhancing kaiC expression.

  • Present address: Division of Biological Informatics, Graduate School of Human Informatics, Nagoya University, Chikusa-ku, Nagoya, Aichi 464-8601, Japan.

  • Present address: Department of Cell Biology, Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA, 92037, USA.

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