FIGURE 1.

Epigenetic regulation of gene expression by circadian clock. CLOCK can acetylate histones to induce gene expression. CLOCK interacts with MLL1 (a histone methyltransferase) and SIRT1 (a deacetylase).These epigenetic regulators can modify the chromatin according the environmental stimuli, such as nutrient availability. Furthermore, REV-ERBα, a clock-controlled gene, can cause recruitment of HDAC3 and deacetylate histones. Circadian regulation of either the expression or the activity of these epigenetic regulators determines whether the gene gets turned “ON” or “OFF.”