Force-induced melting of a short DNA double helix

The dynamic behaviour of DNA is of fundamental importance to many cellular processes. One principal characteristic, central to transcription and repli cation, is the ability of the duplex to "melt". It has recently been shown that dynamic force spectroscopy provides information about the energetics o f biomolecular dissociation. We have employed this technique to investigate the unbinding of single dodecanucleotide molecules. To separate the duplex to single-stranded DNA, forces ranging from 17 to 40 pN were required over a range of loading rates. Interpretation of the dependence of melting forc e on loading rate revealed that the energy barrier to rupture is between 9 and 13 kcal mol(-1) in height and situated 0.58 nm from an intermediate str uctural state. Thermal melting studies show that, prior to dissociation, th e oligonucleotide underwent a transition which required between 7 and II kc al mol(-1) in energy. Through combined dynamic force spectroscopy and therm al melting studies we show the derivation of an energy landscape to dissoci ate a 12-mer duplex. Until very recently, this type of information was only accessible by computational analysis. Additionally, the force spectroscopy data allow an estimation of the kinetics of duplex formation and melting.