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Bacterial physiology

All around the clock

Nature Reviews Microbiology volume 9, page 151 (2011)Cite this article

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the circadian clock is directly entrained by changes in energy metabolism

In the marine cyanobacterium Synechococcus elongatus, the core circadian clock consists of three proteins, KaiA, KaiB and KaiC, that mediate daily changes in gene expression. KaiA and KaiB modulate the autophosphorylation of KaiC, resulting in stable oscillations in the amount of phosphorylated KaiC. To study how changes in illumination affected the circadian clock, Rust and co-workers used synchronized cultures of a strain of S. elongatus that carried a clock-driven bioluminescent reporter. When placed under constant illumination, the cultures retained a subjective 'day–night' cycle of reporter activity. Pulses of darkness produced a decrease in the cellular ATP/ADP ratio; however, only those pulses applied during the subjective 'day' induced phase shifts in the circadian clock and the rhythm of KaiC phosphorylation. Remarkably, manipulation of the ATP/ADP ratio in an in vitro system containing purified KaiA, KaiB and KaiC resulted in similar phase shifts in the rhythm of KaiC phosphorylation. Further in vitro experiments indicated that increased ADP concentrations alter the oscillation phase through inhibition of the kinase activity of KaiC. Thus, KaiC seems to integrate clock information (through the kinase-stimulating activity of KaiA) with metabolic information (through the adenosine pool).

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References

ORIGINAL RESEARCH PAPERS

  1. Rust, M. J., Golden, S. S. and O'Shea, E. K. Light-driven changes in energy metabolism directly entrain the cyanobacterial circadian oscillator. Science 331, 220–223 (2011)

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  2. Saito, M. A. et al. Iron conservation by reduction of metalloenzyme inventories in the marine diazotroph Crocosphaera watsonii. Proc. Natl Acad. Sci. USA 19 January 2011 (doi: 10.1073/pnas.1006943108)

FURTHER READING

  1. Golden, S. S. & Canales, S. R. Cyanobacterial circadian clocks — timing is everything. Nature Rev. Microbiol. 1, 191–199 (2003)

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Authors
  1. Cesar Sanchez
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Sanchez, C. All around the clock. Nat Rev Microbiol 9, 151 (2011). https://doi.org/10.1038/nrmicro2529

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