The interaction between a tandem repeat of the SPKK peptide motif and calf thymus DNA or several polynucleotides has been investigated by circular dichroism. The octapeptide SPKKSPKK does not induce any important changes in the CD spectra of the polynucleotides poly(dG) · poly(dC), poly(dG-dC) · poly(dG-dC) and poly(dA) · poly(dT) while the spectrum of calf thymus DNA is slightly modified. Binding of this basic peptide to the alternating copolymer poly(dA-dT) · poly(dA-dT) results in a marked Ψ-type condensation in a manner similar to that induced by the entire C-terminal domain of histone H1.
