The Influence of the 2′OH Group upon the Binding of Nucleotides by Basic Polyamino Acids

The position of the phosphate group on the ribose of nucleoside monophosphates markedly influences their binding behavior with basic polyamino acids, such as poly‐ l ‐lysine and poly‐ l ‐arginine. Equilibrium dialysis of adenine and guanine derivatives has revealed that the binding of 5′‐ and 3′‐ribonucleotides (group I, possessing a free 2′OH group) to basic polyamino acids is clearly different from that of 2′‐ribo and 5′‐deoxyribonucleotides (group II, the 2′OH group is blocked and absent, respect.). At low nucleotide to poly‐ l ‐lysine ratios, where the binding corresponds to the Langmuir isotherm, the binding constants of group I are smaller than those of group II. At higher nucleotide to polypeptide ratios the binding is cooperative and accompanied by a phase transition: guanine derivatives of group I show precipitation with poly‐ l ‐lysine at 0′, whereas with group II a gel‐like phase is separated; with poly‐ l ‐arginine only precipitation occurs. Analysis of the cooperative binding with guanine nucleotides and poly‐ l ‐arginine revealed that group I possesses considerably higher nearest neighbour interaction energies than group II. The stacking coefficients decrease in the order 3′‐GMP > 5′‐GMP > 5′‐dGMP > 2′‐GMP. The implications of these results are discussed.