The invention provides methods and compositions for modulating the life span of eukaryotic and prokaryotic cells and for protecting cells against certain stresses, e.g., heatshock. One method comprises modulating the flux of the NAD+ salvage pathway in the cell, e.g., by modulating the level or activity of one or more proteins selected from the group consisting of NPT1, PNC1, NMA1 and NMA2. Another method comprises modulating the level of nicotinamide in the cell.
