Fig. 2.

Timetable for actions of clock-associated proteins. Genes colored in red act in the morning (‘early shift’), green-colored genes are active from early daytime until midnight, and light blue and orange genes act during the night. (A) In the morning, LHY and CCA1 proteins repress the evening-phase genes LUX, TOC1 and ELF4, and activate the day-phase genes PRR9 and PRR7. (B) From early daytime until midnight, PRR9, PRR7 and PRR5 repress the morning-phase genes CCA1 and LHY. Blue light enhances interaction of ZTL and GI. In the dark, the ZTL–GI complex is decoupled, allowing ZTL to promote the degradation of PRR5. (C) In the evening, LUX represses PRR9 and LUX expression, and ELF4 and ELF3 repress PRR9 and PRR7. PRR5 enhances nuclear localization of TOC1, and PRR3 stabilizes TOC1 in the evening. On the other hand, ZTL promotes the degradation of PRR5 and TOC1 at night (in darkness). TOC1 acts to activate CCA1 expression by antagonizing CHE on the CCA1 promoter. (D) Genetic circuit in the clock. CCA1 and LHY activate PRR9 and PRR7, and repress TOC1, ELF4 and LUX. ELF4, LUX and ELF3 repress PRR9 and PRR7. PRR9, PRR7 and PRR5 repress CCA1 and LHY, whereas TOC1 activates CCA1. These interactions illustrate the ‘genetic circuit’, which underlies the 24 h endogenous cycle.