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PER-dependent rhythms in CLK phosphorylation and E-box binding regulate circadian transcription
Wangjie Yu1, Hao Zheng, Jerry H Houl
1Department of Biology and Biochemistry, University of Houston, Houston, Texas 77204-5001, USA.
Genes & Development
|March 18, 2006
Summary
The PERIOD-TIMELESS complex inhibits CLOCK-CYCLE binding to DNA, preventing transcription. This interaction triggers CLOCK phosphorylation and degradation, allowing transcription to resume.
Area of Science:
- Molecular Biology
- Chronobiology
- Genetics
Background:
- Circadian rhythms are regulated by transcriptional-translational feedback loops.
- In Drosophila, CLOCK-CYCLE (CLK-CYC) activates transcription, while PERIOD-TIMELESS (PER-TIM) represses it.
Purpose of the Study:
- To elucidate the molecular mechanism by which PER-TIM represses CLK-CYC transcriptional activity.
- To investigate the role of CLK phosphorylation in regulating circadian gene expression.
Main Methods:
- In vivo analysis of CLK-CYC binding to E-box elements.
- Co-immunoprecipitation assays to study protein interactions.
- Phosphorylation state analysis of CLK and PER proteins.
Main Results:
- PER-TIM interaction with CLK-CYC inhibits CLK-CYC binding to E-box regulatory elements.
- PER-TIM binding induces CLK hyperphosphorylation, involving DOUBLE-TIME (DBT) kinase.
- DBT destabilizes CLK and PER, leading to their degradation.
- Hypophosphorylated CLK accumulates, binds E-boxes, and activates transcription.
Conclusions:
- PER-dependent rhythms in CLK phosphorylation control circadian transcription and CLK stability.
- This mechanism links PER and CLK function in the fly circadian cycle.
- The fly circadian feedback mechanism differs from that observed in mammals.