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Science 31 October 2008:
Vol. 322. no. 5902, pp. 697 - 701
DOI: 10.1126/science.1150451
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Review

Structural Insights into a Circadian Oscillator

Carl Hirschie Johnson,1* Martin Egli,2 Phoebe L. Stewart3

An endogenous circadian system in cyanobacteria exerts pervasive control over cellular processes, including global gene expression. Indeed, the entire chromosome undergoes daily cycles of topological changes and compaction. The biochemical machinery underlying a circadian oscillator can be reconstituted in vitro with just three cyanobacterial proteins, KaiA, KaiB, and KaiC. These proteins interact to promote conformational changes and phosphorylation events that determine the phase of the in vitro oscillation. The high-resolution structures of these proteins suggest a ratcheting mechanism by which the KaiABC oscillator ticks unidirectionally. This posttranslational oscillator may interact with transcriptional and translational feedback loops to generate the emergent circadian behavior in vivo. The conjunction of structural, biophysical, and biochemical approaches to this system reveals molecular mechanisms of biological timekeeping.

1 Department of Biological Sciences, Box 35-1634, Vanderbilt University, Nashville, TN 37235–1634, USA.
2 Department of Biochemistry, Vanderbilt University, Nashville, TN 37235–0146, USA.
3 Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37235–0615, USA.

* To whom correspondence should be addressed. E-mail: carl.h.johnson{at}vanderbilt.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Metabolic Rhythms of the Cyanobacterium Cyanothece sp. ATCC 51142 Correlate with Modeled Dynamics of Circadian Clock.
J. Cerveny and L. Nedbal (2009)
J Biol Rhythms 24, 295-303
   Abstract »    PDF »
The Evolution of the Cyanobacterial Posttranslational Clock from a Primitive "Phoscillator".
M. J.P. Simons (2009)
J Biol Rhythms 24, 175-182
   Abstract »    PDF »


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Science. ISSN 0036-8075 (print), 1095-9203 (online)