Daily cycles of per and tim gene activity and DNA packaging controlled by CLK-CYC binding rhythm

Rhythmic transcription of the per and tim genes involves time-of-day-specific binding of CLK-CYC and associated chromatin modifications.

• Activation of per and tim transcription occurs alongside CLK-CYC binding to E-boxes and specific histone modifications.
• Histone H3-K9 acetylation and H3-K4 trimethylation are observed during the activation phase of these genes.
• RNA polymerase II binding to the tim promoter is linked to transcriptional elongation, while it remains constantly bound to the per promoter.
• Repression of transcription is associated with the reversal of these modifications by PER.
• Similar rhythmic histone modifications are linked to CLOCK-BMAL1-dependent transcription in mammals, suggesting a conserved mechanism across species.

Simplified