To provide a nuclear transport agent, a gene transfer system comprising the nuclear transport agent, a method of transporting DNA into the nucleus of eukaryotic cells using the nuclear transport agent and the use of the nuclear transport agent in gene therapy for treating cancer, viral infections, diseases of the nervous system, graft rejection and monogenic or polygenic hereditary diseases.

The nuclear transporting agent comprises two modules A and B, wherein the module A binds specifically to a DNA molecule so as not to form complexes consisting of more than one DNA molecule, and wherein the module B comprises an extended nuclear localization signal having a charge thus preventing the second module from mediating nonspecific binding of the nuclear transport agent to the DNA molecule.