Proteasome function is required for biological timing throughout the twenty-four hour cycle

Area of Science:

• Chronobiology
• Molecular Biology
• Cellular Biology

Background:

• Circadian clocks were traditionally viewed as driven by transcriptional/translational feedback loops (TTFLs).
• Recent discoveries highlighted the importance of posttranslational modifications and protein degradation in circadian timing across taxa.
• Evidence in Ostreococcus tauri suggested transcription-independent oscillations.

Purpose of the Study:

• To investigate the role of targeted protein degradation in the Ostreococcus tauri circadian clock mechanism.
• To analyze the interplay between TTFLs, protein modification, and degradation in circadian timing.
• To determine if protein degradation is essential for sustaining TTFL rhythmicity.

Main Methods:

• Utilized Ostreococcus tauri as a model system.
• Employed luciferase reporter fusion proteins to quantify CCA1 and TOC1 protein content and degradation rates.
• Measured protein degradation rates with high time resolution under constant conditions and in response to darkness.

Main Results:

• Identified a TTFL involving CCA1 and TOC1 proteins in Ostreococcus.
• Demonstrated clock-regulated peaks in CCA1 protein degradation under constant conditions.
• Showed that TOC1 degradation peaks in response to darkness.
• Established targeted protein degradation as essential for sustaining TTFL rhythmicity, even in transcriptionally inactive cells.

Conclusions:

• Targeted protein degradation plays a central role in the mechanism of circadian timing.
• Proteasome function is crucial for sustaining both TTFL and posttranslational circadian oscillations.
• Circadian timing relies on a coordinated interplay of transcription, translation, and targeted protein degradation.