AbstractThe synthesis and characterization of the block copolypeptide (Leu67, Lys33)100Orn20, a synthetic model of histone, are reported. In neutral aqueous solutions, 80% of the etheropolypeptide block assumes an α‐helical conformation, whereas the polyornithine block is in a random‐coil conformation. In the association complexes with DNA, melting and titration experiments, as well as CD results, indicate that the polyornithine block interacts with DNA, whereas at least 2/3 of the lysine residues of the (Leu, Lys) moiety are excluded from the direct binding with DNA. CD spectra of the association complexes reveal significant differences from those obtained with DNA–polyornithine and DNA–polylysine complexes but substantial similarities with CD spectra of native and reconstituted nucleohistones. In contrast to DNA–polyornithine complexes, the CD spectra of the ternary complexes, copolypeptide–DNA–ethidium bromide, indicate a strong reduction of the dye intercalation. The low‐angle x‐ray diffraction pattern, reminiscent of that of chromatin, reveals the presence of a superstructure in these complexes. The results obtained are discussed in connection with the expected structural fea