Base-base mismatches. Thermodynamics of double helix formation for dCA3XA3G + dCT3YT3G (X, Y = A,C,G,D

Thermodynamic parameters for double strand formation have been measured for the sixteen double helices of the sequence dCA3XA3G.dCT3YT3G, with each of the bases A, C, G and T at the positions labelled X and Y. The results are analyzed in terms of nearest-neighbors and are compared with thermodynamic parameters for RNA secondary structure. At room temperature the sequence (Formula: see text) is more stable than (Formula: see text) and is similar in stability to (Formula: see text) and (Formula: see text) are least stable. At higher temperatures the sequences containing a G.C base pair become more stable than those containing only A.T. All molecules containing mismatches are destabilized with respect to those with only Watson-Crick pairing, but there is a wide range of destabilization. At room temperature the most stable mismatches are those containing guanine (G.T, G.G, G.A); the least stable contain cytosine (C.A, C.C). At higher temperatures pyrimidine-pyrimidine mismatches become the least stable.