CLOCKWORK ORANGE Enhances PERIOD Mediated Rhythms in Transcriptional Repression by Antagonizing E-box Binding by CLOCK-CYCLE

• Published in: PLoS genetics Vol. 12; no. 11; p. e1006430
• Main Authors: Zhou, Jian, Yu, Wangjie, Hardin, Paul E
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 04-11-2016; Public Library of Science (PLoS)
• Subjects: Animals; ARNTL Transcription Factors - genetics; ARNTL Transcription Factors - metabolism; Binding sites (Biochemistry); Biological clocks; Biology; Biology and life sciences; Circadian rhythm; Circadian Rhythm - genetics; Circadian rhythms; CLOCK Proteins - genetics; CLOCK Proteins - metabolism; Colleges & universities; Deoxyribonucleic acid; DNA; Drosophila; Drosophila melanogaster - genetics; Drosophila Proteins - genetics; Drosophila Proteins - metabolism; E-Box Elements; Feedback; Funding; Gene Expression Regulation; Genetic aspects; Insects; Metabolism; Observations; Period Circadian Proteins - genetics; Period Circadian Proteins - metabolism; Physiology; Proteins; Repressor Proteins; Research and Analysis Methods; Rodents; Transcription (Genetics); Transcription factors; Transcription, Genetic; United States > US; Texas
• ISSN: 1553-7404; 1553-7390; 1553-7404
• DOI: 10.1371/journal.pgen.1006430

The Drosophila circadian oscillator controls daily rhythms in physiology, metabolism and behavior via transcriptional feedback loops. CLOCK-CYCLE (CLK-CYC) heterodimers initiate feedback loop function by binding E-box elements to activate per and tim transcription. PER-TIM heterodimers then accumulate, bind CLK-CYC to inhibit transcription, and are ultimately degraded to enable the next round of transcription. The timing of transcriptional events in this feedback loop coincide with, and are controlled by, rhythms in CLK-CYC binding to E-boxes. PER rhythmically binds CLK-CYC to initiate transcriptional repression, and subsequently promotes the removal of CLK-CYC from E-boxes. However, little is known about the mechanism by which CLK-CYC is removed from DNA. Previous studies demonstrated that the transcription repressor CLOCKWORK ORANGE (CWO) contributes to core feedback loop function by repressing per and tim transcription in cultured S2 cells and in flies. Here we show that CWO rhythmically binds E-boxes upstream of core clock genes in a reciprocal manner to CLK, thereby promoting PER-dependent removal of CLK-CYC from E-boxes, and maintaining repression until PER is degraded and CLK-CYC displaces CWO from E-boxes to initiate transcription. These results suggest a model in which CWO co-represses CLK-CYC transcriptional activity in conjunction with PER by competing for E-box binding once CLK-CYC-PER complexes have formed. Given that CWO orthologs DEC1 and DEC2 also target E-boxes bound by CLOCK-BMAL1, a similar mechanism may operate in the mammalian clock.