The eukaryotic translation initiation factor 5A (eIF5A) is the only protein that contains hypusine [N e -(4-amino-2-hydroxybutyl)lysine], which is required for its activity. Hypusine is formed by post-translational modifica-tion of one specific lysine (Lys50 for human eIF5A) by deoxyhypusine syn-thase and deoxyhypusine hydroxylase.