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. Author manuscript; available in PMC: 2017 Jun 15.
Published in final edited form as: Curr Opin Genet Dev. 2014 Jul 15;26:66–72. doi: 10.1016/j.gde.2014.06.003

Figure 1.

Figure 1

The NAD+ salvage pathway and its control by the circadian clock. The biosynthesis of NAD+ follows a circadian pattern, which is caused by the circadian expression of NAMPT, a rate-limiting enzyme in the NAD+ biosynthetic salvage pathway. The Nampt gene contains E-boxes in its promoter, leading to direct transcriptional control by the dimer CLOCK:BMAL1. The fluctuating levels of NAD+ modulate the activity of SIRT1 which in turn regulates the transcriptional activity of CLOCK:BMAL1 on their targets genes. During the aging the levels of NAD+ decreases and might alter the circadian rhythms of clock-controlled genes (CCGs)