Circadian rhythms persist without transcription in a eukaryote

Nature. 2011 Jan 27;469(7331):554-8. doi: 10.1038/nature09654.


Circadian rhythms are ubiquitous in eukaryotes, and coordinate numerous aspects of behaviour, physiology and metabolism, from sleep/wake cycles in mammals to growth and photosynthesis in plants. This daily timekeeping is thought to be driven by transcriptional-translational feedback loops, whereby rhythmic expression of 'clock' gene products regulates the expression of associated genes in approximately 24-hour cycles. The specific transcriptional components differ between phylogenetic kingdoms. The unicellular pico-eukaryotic alga Ostreococcus tauri possesses a naturally minimized clock, which includes many features that are shared with plants, such as a central negative feedback loop that involves the morning-expressed CCA1 and evening-expressed TOC1 genes. Given that recent observations in animals and plants have revealed prominent post-translational contributions to timekeeping, a reappraisal of the transcriptional contribution to oscillator function is overdue. Here we show that non-transcriptional mechanisms are sufficient to sustain circadian timekeeping in the eukaryotic lineage, although they normally function in conjunction with transcriptional components. We identify oxidation of peroxiredoxin proteins as a transcription-independent rhythmic biomarker, which is also rhythmic in mammals. Moreover we show that pharmacological modulators of the mammalian clock mechanism have the same effects on rhythms in Ostreococcus. Post-translational mechanisms, and at least one rhythmic marker, seem to be better conserved than transcriptional clock regulators. It is plausible that the oldest oscillator components are non-transcriptional in nature, as in cyanobacteria, and are conserved across kingdoms.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biomarkers / analysis
  • Chlorophyta / drug effects
  • Chlorophyta / metabolism
  • Chlorophyta / physiology*
  • Circadian Rhythm / physiology*
  • Cycloheximide / pharmacology
  • Deoxyadenosines / pharmacology
  • Gene Expression Regulation / drug effects
  • Oxidation-Reduction
  • Peroxiredoxins / metabolism
  • Protein Synthesis Inhibitors / pharmacology
  • Transcription, Genetic*


  • Biomarkers
  • Deoxyadenosines
  • Protein Synthesis Inhibitors
  • Cycloheximide
  • Peroxiredoxins
  • cordycepin