Detection of T-T mismatches using mass spectrometry: specific interactions of Hg(II) with oligonucleotides rich in thymine (T).

Electrospray ionization tandem mass spectrometry (ESI-MS/MS) was employed in a detailed study of the interactions of mercury dications with selected oligodeoxynucleotides rich and poor in thymine (T): d(5'-TT-3'), d(5'-TTT-3'), d(5'-TTTT-3'), d(5'-GG-3'), d(5'-CC-3'), d(5'-AA-3'), d(5'-GCTTGC-3'), d(5'-GTGCTC-3'), d(5'-GCATGC-3'), and d(5'-GCGCGC-3'). Specific interactions are observed for Hg(2+) with pure and mixed thymine sequences in which simultaneous bonding between two thymine units is indicated, and this is consistent with a model proposed in the literature in which Hg(2+) covalently coordinates to two thymines by replacing two N3 imino protons of the bases. The ESI-MS/MS measurements, combined with data on the thermal stability of mixed sequence hexadeoxynucleotides, indicate that mercury prefers thymines over the other binding sites in oligonucleotides both in solution and in the gas phase. These results point toward the effective use of Hg(2+) in the fast detection of mismatch base pairs incorporated in oligonucleotide duplexes and longer mixed DNA sequences using ESI-MS/MS.