PER-dependent rhythms in CLK phosphorylation and E-box binding regulate circadian transcription.
Transcriptional activation by CLOCK-CYCLE (CLK-CYC) heterodimers and repression by PERIOD-TIMELESS (PER-TIM) heterodimers are essential for circadian oscillator function in Drosophila. PER-TIM was previously found to interact with CLK-CYC to repress transcription, and here we show that this interaction inhibits binding of CLK-CYC to E-box regulatory elements in vivo. Coincident with the interaction between PER-TIM and CLK-CYC is the hyperphosphorylation of CLK. This hyperphosphorylation occurs in parallel with the PER-dependent entry of DOUBLE-TIME (DBT) kinase into a complex with CLK-CYC, where DBT destabilizes both CLK and PER. Once PER and CLK are degraded, a novel hypophosphorylated form of CLK accumulates in parallel with E-box binding and transcriptional activation. These studies suggest that PER-dependent rhythms in CLK phosphorylation control rhythms in E-box-dependent transcription and CLK stability, thus linking PER and CLK function during the circadian cycle and distinguishing the transcriptional feedback mechanism in flies from that in mammals.
Yu
Wangjie
W
Department of Biology and Biochemistry, University of Houston, Houston, Texas 77204-5001, USA.
Zheng
Hao
H
Houl
Jerry H
JH
Dauwalder
Brigitte
B
Hardin
Paul E
PE
D000818:Animals; D001483:Base Sequence; D056926:CLOCK Proteins; D002478:Cells, Cultured; D002940:Circadian Rhythm; D017931:DNA Primers; D004330:Drosophila; D029721:Drosophila Proteins / Q000378:metabolism*; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic
C120526:Clk protein, Drosophila; D017931:DNA Primers; D029721:Drosophila Proteins; D014157:Transcription Factors; D056926:CLOCK Proteins