The present invention relates to nucleic acid molecules encoding hypusines mutants having the biological activity of an inhibitor of cellular proliferation. The present invention further relates to vectors comprising said nucleic acid molecules, to hosts transformed with said vectors, to methods of producing the polypeptide encoded by the nucleic acid molecule of the invention as well as to the polypeptide itself. In addition, the present invention relates to pharmaceutical and diagnostic compositions comprising one or more of the aforementioned compounds, the methods for synchronizing cell growth and to the use of the vector of the invention in gene therapy.