Eukaryotic translation initiation factor 5A (eIF5A) is the only protein Known to contain unusual amino acid formed by the action of deoxyhypusine synthase and deoxyhypusine hydroxylase using spermidine as the substrate. This protein was previously reported to be involved in the first step of peptide bond formation in translation; however more recent work implicates it as a universally conserved translation elongation factor.