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Science. 2015 Jul 17;349(6245):324-8. doi: 10.1126/science.1260031. Epub 2015 Jun 25.

Circadian rhythms. A protein fold switch joins the circadian oscillator to clock output in cyanobacteria.

Author information

1
School of Natural Sciences, University of California, Merced, CA 95343, USA.
2
Center for Circadian Biology, University of California, San Diego, La Jolla, CA 92093, USA.
3
Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA.
4
Department of Chemistry, University of California, Davis, CA 95616, USA.
5
School of Natural Sciences, University of California, Merced, CA 95343, USA. Quantitative and Systems Biology, University of California, Merced, CA 95343, USA.
6
Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA.
7
Department of Medicine, University of California, San Diego, La Jolla, CA 92093, USA.
8
Center for Circadian Biology, University of California, San Diego, La Jolla, CA 92093, USA. Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA.
9
School of Natural Sciences, University of California, Merced, CA 95343, USA. Center for Circadian Biology, University of California, San Diego, La Jolla, CA 92093, USA. Quantitative and Systems Biology, University of California, Merced, CA 95343, USA. Chemistry and Chemical Biology, University of California, Merced, CA 95343, USA. Health Sciences Research Institute, University of California, Merced, CA 95343, USA. aliwang@ucmerced.edu.

Abstract

Organisms are adapted to the relentless cycles of day and night, because they evolved timekeeping systems called circadian clocks, which regulate biological activities with ~24-hour rhythms. The clock of cyanobacteria is driven by a three-protein oscillator composed of KaiA, KaiB, and KaiC, which together generate a circadian rhythm of KaiC phosphorylation. We show that KaiB flips between two distinct three-dimensional folds, and its rare transition to an active state provides a time delay that is required to match the timing of the oscillator to that of Earth's rotation. Once KaiB switches folds, it binds phosphorylated KaiC and captures KaiA, which initiates a phase transition of the circadian cycle, and it regulates components of the clock-output pathway, which provides the link that joins the timekeeping and signaling functions of the oscillator.

PMID:
26113641
PMCID:
PMC4506712
DOI:
10.1126/science.1260031
[Indexed for MEDLINE]
Free PMC Article

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