Single-molecule derivation of salt dependent base-pair free energies in DNA

Proc Natl Acad Sci U S A. 2010 Aug 31;107(35):15431-6. doi: 10.1073/pnas.1001454107. Epub 2010 Aug 17.


Accurate knowledge of the thermodynamic properties of nucleic acids is crucial to predicting their structure and stability. To date most measurements of base-pair free energies in DNA are obtained in thermal denaturation experiments, which depend on several assumptions. Here we report measurements of the DNA base-pair free energies based on a simplified system, the mechanical unzipping of single DNA molecules. By combining experimental data with a physical model and an optimization algorithm for analysis, we measure the 10 unique nearest-neighbor base-pair free energies with 0.1 kcal mol(-1) precision over two orders of magnitude of monovalent salt concentration. We find an improved set of standard energy values compared with Unified Oligonucleotide energies and a unique set of 10 base-pair-specific salt-correction values. The latter are found to be strongest for AA/TT and weakest for CC/GG. Our unique energy values and salt corrections improve predictions of DNA unzipping forces and are fully compatible with melting temperatures for oligos. The method should make it possible to obtain free energies, enthalpies, and entropies in conditions not accessible by bulk methodologies.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Algorithms
  • Base Pairing*
  • Base Sequence
  • DNA / chemistry*
  • DNA, Single-Stranded / chemistry
  • Entropy
  • Models, Chemical
  • Monte Carlo Method
  • Nucleic Acid Conformation / drug effects
  • Nucleic Acid Denaturation / drug effects
  • Sodium Chloride / chemistry
  • Sodium Chloride / pharmacology
  • Thermodynamics*
  • Transition Temperature


  • DNA, Single-Stranded
  • Sodium Chloride
  • DNA