Study by Na-23-NMR, H-1-NMR, and ultraviolet spectroscopy of the thermal stability of an 11-basepair oligonucleotide

Na-23-NMR, H-1-NMR, and ultraviolet (UV) spectroscopy have been used to stu dy the thermal stability of the double helix structure of an 11-basepair ol igonucleotide. The denaturation curves obtained by Na-23-NMR and UV are ana lyzed using a two-state model. The melting temperature and Delta H-0 obtain ed are identical within experimental error, suggesting that modifications i n the ionic atmosphere, probed by 23Na-NMR, and the modifications in the ba sepair stacking, probed by UV, occur at the same temperature. Additional dy namical information on the denaturation process has been obtained by H-1-NM R: slow exchange is observed between the thymine methyl resonances, and the disappearance of imino protons shows that a single basepair opening does n ot contribute significantly to proton exchange.