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.
Department of Biology and Biochemistry, University of Houston, Houston, Texas 77204-5001, USA.
Wangjie
W
Yu
Hao
H
Zheng
Jerry H
JH
Houl
Brigitte
B
Dauwalder
Paul E
PE
Hardin
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