The invention pertains to a nucleic acid transfer system including a translocation domain of toxins, especially of diphtheria toxin suitable for targeting a nucleic acid, e.g. a gene, to a specific cell, and obtaining expression of said nucleic acid. The nucleic acid transfer system of the invention comprises a multidomain protein component and a nucleic acid component. Furthermore, the present invention relates to the multidomain protein, a nucleic acid encoding said protein, suitable amplification and expression systems for said nucleic acid, and processes for the preparation and uses of the above subject matters.