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. Author manuscript; available in PMC: 2013 Jun 4.
Published in final edited form as: Cell. 2008 Jul 25;134(2):212–214. doi: 10.1016/j.cell.2008.07.010

Figure 1. The Circadian Rhythm of Acetylation and Deacetylation.

Figure 1

During the activation phase, CLOCK-BMAL1 is associated with the E-box promoter element and CLOCK mediates acetylation of histone tails. BMAL1 then becomes acetylated and recruits PER2-CRY1. PER2 is acetylated and curtails the activation phase. Systematic NAD+-dependent deacetylation by SIRT of histones, BMAL1, and finally PER2 facilitates the establishment of a repressive chromatin state. For simplicity, SIRT1 is shown only when active.