The CK2 kinase stabilizes CLOCK and represses its activity in the Drosophila circadian oscillator

PLoS Biol. 2013;11(8):e1001645. doi: 10.1371/journal.pbio.1001645. Epub 2013 Aug 27.


Phosphorylation is a pivotal regulatory mechanism for protein stability and activity in circadian clocks regardless of their evolutionary origin. It determines the speed and strength of molecular oscillations by acting on transcriptional activators and their repressors, which form negative feedback loops. In Drosophila, the CK2 kinase phosphorylates and destabilizes the PERIOD (PER) and TIMELESS (TIM) proteins, which inhibit CLOCK (CLK) transcriptional activity. Here we show that CK2 also targets the CLK activator directly. Downregulating the activity of the catalytic α subunit of CK2 induces CLK degradation, even in the absence of PER and TIM. Unexpectedly, the regulatory β subunit of the CK2 holoenzyme is not required for the regulation of CLK stability. In addition, downregulation of CK2α activity decreases CLK phosphorylation and increases per and tim transcription. These results indicate that CK2 inhibits CLK degradation while reducing its activity. Since the CK1 kinase promotes CLK degradation, we suggest that CLK stability and transcriptional activity result from counteracting effects of CK1 and CK2.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • CLOCK Proteins / genetics
  • CLOCK Proteins / metabolism*
  • Circadian Rhythm / genetics
  • Circadian Rhythm / physiology*
  • Drosophila
  • Drosophila Proteins / genetics
  • Drosophila Proteins / metabolism*
  • Phosphorylation


  • Drosophila Proteins
  • tim protein, Drosophila
  • CLOCK Proteins

Grant support

This work was funded by Agence Nationale de la Recherche “DrosoClock”, “ClockGene” and “FunGenDroso”, “Equipe FRM” program of Fondation pour la Recherche Médicale, and European Union 6th Framework Programme “EUCLOCK”. AS was partly supported by Association pour la Recherche sur le Cancer and FR is supported by Institut National de la Santé et des Etudes et Recherches Médicales. TR was funded by the DFG SFB1047 grant from Deutsche Forschungsgemeinschaft. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.