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Circadian clock control of interactions between eIF2α kinase CPC-3 and GCN1 with ribosomes regulates rhythmic

Ebimobowei O Preh1, Manuel A Ramirez1, Sidharth Mohan1

  • 1Department of Biology and Center for Biological Clocks Research, Texas A&M University, College Station, TX 77843.

Proceedings of the National Academy of Sciences of the United States of America
|February 4, 2025
PubMed

Insights

Circadian rhythms control protein synthesis by regulating GCN2 kinase activity. The clock synchronizes uncharged tRNA levels with ribosome interactions, ensuring efficient mRNA translation and cellular energy balance.

Area of Science:

  • Molecular Biology
  • Circadian Biology
  • Biochemistry

Background:

  • GCN2 kinase activity, crucial for regulating translation initiation factor eIF2α, is implicated in various health disorders.
  • Nutrient starvation activates GCN2 via uncharged tRNA binding to GCN1 and GCN20.
  • In *Neurospora crassa*, the GCN2 homolog CPC-3 is under circadian clock control, but the mechanism remained unclear.

Purpose of the Study:

  • To elucidate the mechanism by which the circadian clock controls the rhythmic activity of CPC-3.
  • To investigate the role of ribosome interactions and uncharged tRNA levels in circadian regulation of CPC-3.

Main Methods:

  • Analysis of CPC-3 and GCN1 interaction with ribosomes under circadian control.
  • Utilized a temperature-sensitive valyl-tRNA synthetase mutant (*un-3*) to assess the impact of constant uncharged tRNA levels.
  • Investigated the effect of disrupting GCN1 and uncharged tRNA interaction on CPC-3 activity rhythms.

Main Results:

  • The circadian clock regulates the interaction of CPC-3 and GCN1 with ribosomes, which is essential for CPC-3 activity rhythms.
  • Rhythmic CPC-3 activity and its interaction with ribosomes were abolished in the *un-3* mutant with constitutive high uncharged tRNA levels.
  • The clock controls uncharged tRNA and GCN1 interaction, as disrupting this linkage altered CPC-3 activity rhythms.

Conclusions:

  • Circadian rhythms in mRNA translation, mediated by CPC-3, depend on rhythmic fluctuations in uncharged tRNA levels.
  • These tRNA rhythms drive the rhythmic association of CPC-3 and GCN1 with ribosomes.
  • This regulatory mechanism ensures temporal coordination between cellular energy status and the energy-intensive process of mRNA translation.
Keywords:
circadian clockeIF2αribosometRNA synthetasetranslation initiation

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