the present invention relates to a method for transfection of cells using at least one protein capable of forming nucleoprotein filaments , wherein the protein is initially modified with at least one functional component which influences one or more steps of the transfection , the nucleic acid to be transfected is then loaded with the modified protein , whereby the nucleic acid and the protein form a filament - like complex , and this complex is finally added to the cells to be transfected . the invention further relates to a transfection agent consisting of nucleoprotein filaments , with at least one nucleoprotein filament - forming protein being modified with at least one functional component for the transfection . furthermore , the present invention relates to the use of the transfection agent according to the invention for producing a drug for gene therapeutic treatment of humans and animals . the present inventions also includes corresponding pharmaceutical preparations , especially for use in gene therapy as well as the use of such transfection agents as component in kits .