Self-complementary oligoribonucleotides: adenylic acid-uridylic acid block copolymers.

Abstract

Abstract A series of block oligonucleotides of adenylic and uridylic acid of the form (Ap)m(Up)n−1, where m and n vary individually from 3 to 7, have been prepared. Individual oligonucleotides were shown to form bimolecular helical complexes in solution when m ⩾ n but when m For m = n the concentration and temperature dependence of association was consistent with a dimer-monomer equilibrium. The concentration dependence of Tm yielded enthalpy changes per base pair, ΔH1, that increased from −6.4 kcal./mole for (Ap)4(Up)3U to −7.6 kcal./mole for (Ap)7(Up)6U. The slope of the thermal dissociation curve at midpoint yielded average values of only −5.5 kcal./ mole. Plots of 1 T m , versus , 1 N , where N = m + n, were linear. However, the apparent variation of ΔH1 had to be introduced in order to obtain values of β that were comparable to other estimates. The chain-length dependence of ΔH1 presumably arises from end effects and/or from variations in the stacking energy of the adenylic acid sequences at the different temperature ranges over which different chain-length dimers dissociated.