Filing Date: 1997-01-28.-- Priority Data: FR 9601004 (1996-01-29).-- International Publication Number: WO_1997028247 (19970807).An oligonucleotide including at least one concatenation coding for a polypeptide of formula (P-K)n, wherein n is an integer of at least 2, P is a proline amino acid residue, K is a lysine amino acid residue, and the sign "-" is a bond, particularly a peptide bond, between the two amino acid residues. The n (P-K) units are also bound together by such bonds, e.g. peptide bonds.