H-1-NMR STUDY OF THE EFFECT OF G-T MISMATCHES ON DYNAMICS AND STABILITY OF D(GCGTGCGC)(2) AND ITS BERENIL COMPLEX

The effects of G-T mismatches on thermal stability, the base-pair life time and the global structure of a d(GCGTGCGC)(2) duplex were studied by using H-1 NMR, UV and CD spectroscopy. The existence of G-T mismatc hes was found to cause a noticeable change in the chemical environment of imino protons associated with significant decrease in the base-pai r lifetime at the mismatched site as well as in thermal stability of t he duplex itself. The melting transition of d(GCGTGCGC)(2) was not coo perative at all at 100 mM or lower concentration of NaCl, but became c ooperative at 500 mM or higher NaCl concentration. The melting tempera ture (T-m) of this duplex was 32 degrees C at 500 mM concentration of NaCl, which is much lower than that of d(GCGCGCGC)(2) at the same NaCl concentration. This suggests that the decrease in stability may be as cribed to the decrease in the base-pair lifetime and the deviation fro m the normal structure due to the G-T mismatches. Adding berenil to d( GCGTGCGC)(2) caused no observable change in the global structure but t he large decrease in the base-pair lifetime and the stability of the d uplex.