FIGURE 2.

Human Pnp but not Mtap functions in yeast NR utilization. A, intracellular NAD⁺ concentrations of the indicated genotypes were measured in NA-free SDC media (black bars) and in NA-free SDC media plus 10 μm NR (gray bars). pMTAP and pPNP indicate the addition of a pRS327 plasmid encoding a human cDNA fused to the yeast PNP1 promoter. Expression of human Pnp allows Nrk1-independent NR utilization. B, all strains are gene silencing-deficient on medium without NA and are gene silencing-proficient on medium with 10 μm NA. 10 μm NR restores gene silencing to wild-type (WT) yeast but not yeast strains lacking both NR salvaging pathways. Human Pnp but not Mtap provides a partial rescue of the gene silencing deficiency, indicating function in NR salvage.