Thermodynamics of dT-dT base pair mismatching in linear DNA duplexes and three-arm DNA junctions

Min Zhong, Luis A. Marky, Neville R. Kallenbach, Donald W. Kupke

Research output: Contribution to journalArticlepeer-review


We have used a combination of magnetic-suspension densimetry and calorimetry to derive complete thermodynamic profiles, including volume changes, for the formation of linear DNA duplexes and three-arm branched DNA junctions, from their component strands, with and without dT-dT mismatches. The formation of each type of complex at 20 °C is accompanied by a favorable free energy, with a favorable enthalpy term partially compensated by an unfavorable entropy. Formation is associated also with net uptake of water molecules. Using the formation of the fully-paired linear duplex or three- arm junction as reference states, we can establish a thermodynamic cycle in which the contribution of the single-strand species cancels. From this cycle, we determine that substitution of dA for dT has a differential free energy of ΔDG°of +2.4 kcal mol-1 for mismatched duplex and +2.0 kcal mol-1 (on the average) for the mismatched junction. These unfavorable differential free energies result from an unfavorable enthalpy, partially compensated by a favorable entropy, and a negative ΔΔV. The free energies in the two cases have signs opposed to those of ΔΔV, a situation that implicates hydration changes in creating the mismatch. When the ΔΔV terms are normalized by the total number of base pairs involved, the immobilization of structural water molecules (and/or substitution of electrostricted for hydrophobic water molecules) is about 7 times greater for junctions than duplexes. This is consistent with more extensive hydrophobic hydration of branched DNA structures than of duplexes.

Original languageEnglish (US)
Pages (from-to)2485-2491
Number of pages7
Issue number9
StatePublished - Mar 4 1997

ASJC Scopus subject areas

  • Biochemistry


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