Figure 1.

Circadian clock genes. The clock process is a stimulatory circle, involving the Bmal1/Clock heterodimer which activates the transcription of Period (Per) and Cryptochrome (Cry) genes, and the inhibitory feedback circle with the Per/Cry heterodimer which translocates to the nucleus and which represses the transcription of the Clock and Bmal1 genes. An additional circle implicates the retinoid-related orphan receptors (RORs) and Rev-Erb factors with a positive feedback by RORs and a negative feedback by Rev-Erb.