FIG. 6.

Model for the regulation of Sir2 activity and life span by nicotinamide. Disparate environmental stimuli including calorie restriction, heat, and osmotic stress serve as inputs to a common pathway of longevity. Cells coordinate a response to these inputs by inducing the transcription of PNC1, which encodes an enzyme that converts nicotinamide to nicotinic acid, thereby alleviating the inhibition of Sir2 and promoting longevity.