Fig. 1

Transcription feedback loops that form the basis of the circadian timing system. The red box denotes the feedback loop centered on the rhythmic expression of period and cryptochrome. The blue box denotes the feedback loop centered on the rhythmic expression of Bmal1 and Rev-Erbα/β. The orange box denotes rhythmic drive that is conferred to core clock-regulated genes (CCGs) via the Bmal1/Clock complex, and via the competitive interaction between Rev-Erbα/β and RORα/β/γ