Figure 1.

The core molecular mechanism of the circadian clock. The molecular clock is composed of diverse autoregulatory feedback loops. The core components of the molecular clock, CLOCK and BMAL1, activate the transcription of repressor clock genes such as Per, Cry, Rev-erbα, and Dec. CLOCK and BMAL1 also activate the transcription of inducer Rorα. The protein products of these repressor or inducer genes inhibit or promote their own transcription in distinct ways, thus forming various feedback loops that create a coordinated circadian rhythm at the gene expression level.