The eukaryotic initiation factor 5A (eIF5A) is the only protein known to contain hypusine, an unusual amino acid formed by the action of deoxyhypusine synthase and deoxyhypusine hydroxylase using spermidine as the substrate. Both eIF5A and deoxyhypusine synthase are essential genes. Modulation of eIF5A has been linked to proliferation and cancer. However, the function of eIF5A is unknown. We have first identified NAD+ as the cofactor for hypusine formation and isolated deoxyhypusine synthase, the key enzyme for hypusine formation. We are interested in every aspects of eIF5A and hypusine formation in living world.