Figure 2.

CLOCK regulates target gene expression. (A) Clock circadian regulator (CLOCK) acetylates brain and muscle ARNT-like 1 (BMAL1) and forms a heterodimer that recruits transcriptional silencer cryptochrome circadian clock 1 (CRY1) or SIN3 Transcription Regulator Family Member B (SIN3B) and histone deacetylase 1/2 (HDAC1/2) to silence period circadian clock 1 (Per1) gene expression. (B) CLOCK/BMAL1 heterodimer recruits sirtuin 1 (SIRT1) to the D-Box Binding PAR BZIP Transcription Factor (Dbp) promoter that rhythmically acetylates histones leading to periodic Dbp gene expression. (C) CLOCK itself rhythmically acetylates histones at Per1 and Dbp gene promoters to regulate transcription. Acetylation is represented by dark red circles.