The interaction of four basic polyamino acids, poly(L-lysine), poly(L-ornithine), poly(L-arginine) and poly(L-homoarginine) with nucleotides was investigated using equilibrium dialysis and circular dichroism. Polyhomoarginine was prepared by guanidization of polylysine. The interaction of 5'-GMP exhibited equal values for the binding cooperativity in all cases, indicating that nucleotidenucleotide interaction, i.e. the stacking tendency of the guanine base, was the origin of this affinity. The affinity parameters of 5'-GMP and other nucleotides directed towards the basic polypeptides, however, decrease in the series: polyarginine > polyhomoarginine > polyornithine > polylysine.This indicates that the ion bond between guanidinium and phosphate is stronger than that between ammonium and phosphate, and that decreasing the length of the poly(amino acid) side chains by one CH2 group results in an increase of affinity. The binding of 3'-GMP and 5'-GMP by polylysine and polyornithine induces a strong negative circular dichroism band in the absorption region of the base and in the case of polylysine also changes at shorter wavelength. Temperature-dependent measurements of these circular dichroic spectra revealed that polylysine fits best to and forms the most stable complexes with helical arrangements of bound GMP molecules.Protein-nucleic acid interactions include long-range electrostatic contributions which originate in the nucleic acid phosphates and the basic amino-acid residues of proteins, such as lysine and arginine. The ionic bond is thought not to exert much specificity. However, the chemical features of the side chains of the two basic amino acids are different enough such that one would except some specific influence on proteinnucleic acid recognition processes. Investigations in this field are chiefly those dealing with polymer-polymer interaction, for example studies of precipitation and melting of DNA * basic poly(amino acid) complexes and observations of spectral features mainly by circular dichroism (for review see [l]).There are also investigations on monomer-polymer interaction involving the binding of nucleotides by basic poly(amino acids), like polylysine and polyarginine [2-91. These offer some advantages over the polymer -polymer interaction mentioned above although they are dealing with some different aspects of the interaction. The former allows the direct determination of affinity data. In the present work comparative Part of this work was presented at the first European Biophysics Congress, Baden near Vienna, 1971.
Abbreviation. CD, circular dichroic.experiments have been performed with poly(L-lysine), poly(L-ornithine), poly(L-arginine) and poly(L-homoarginine), using equilibrium dialysis and circular dichroism, in order to elucidate the influence of the nature of basic amino-acid side chains on the interaction with nucleotides.
MATERIALS AND METHODSNucleotides were purchased from Boehringer Mannheim GmbH (Mannheim, Germany), poly(L-arginine) 0.5 HzS04, poly(L-lysine) HBr and poly(L-ornithine)...