© 2006 Oxford University Press
Structural analyses on the mercuryII-mediated T-T base pair
1 Graduate School of Pharmaceutical Sciences, Tohoku University, Aobayama, Aoba-ku, Sendai 980-8578, Japan, 2 Graduate School of Sciences, NAIST, Ikoma 630-0101, Japan, 3 Department of Material and Life Chemistry, Faculty of Engineering, Kanagawa University, Yokohama 221-8686, Japan
Recently, it was reported that T-T mismatches can specifically recognize HgII, and form T-HgII-T pairs. In order to understand the structure and properties of the T-HgII-T pair, we measured NMR spectra for a DNA duplex, d(CGCGTTGTCC) • d(GGACTTCGCG), with two successive T-T mismatches (HgII-binding sites) in the middle of the duplex. We identified imino proton resonances of the T-T mismatches in mercury-free duplex, and performed titration experiments with HgII by using 1-dimensional (1D) 1H NMR spectra. From the titration spectra, disappearances of imino proton signals were observed upon the addition of HgII. Furthermore, we observed additional signals of transient species, most likely mono-mercurated duplexes. This is an evidence that structural transformations between HgII-free and HgII-bound forms are slow enough for each species to give independent signals. These data strongly suggest that the imino protons of thymine bases were substituted with HgII, to form T-HgII-T pairs in which one HgII cross-links two N3 atoms of thymines.