Proton and phosphorus nuclear magnetic resonance studies of an oligothymidylate covalently linked to an acridine derivative and of its binding to complementary sequences.

An oligodeoxynucleotide containing four thymines and covalently attached to an acridine derivative through its 3'-phosphate [(Tp)4(CH2)5Acr] was synthesized. Its conformation in solution was investigated by proton magnetic resonance. Both intramolecular interactions between the acridine dye and thymines and intermolecular interactions were demonstrated. Both proton and phosphorus magnetic resonances were used to study the specific interaction of (Tp)4(CH2)5Acr with poly(rA) and (Ap)3A. The results were compared to those obtained when the acridine-containing substituent was replaced by an ethyl group attached to the 3'-phosphate of the oligothymidylate. The acridine dye strongly stabilized the complexes formed with both poly(rA) and (Ap)3A. Upfield shifts of both adenine and acridine proton resonances were observed in the complexes. These results were ascribed to an intercalation of the acridine ring between A X T base pairs of the duplex structure formed by the oligothymidylate with its complementary oligoadenylate sequence. An analysis of proton and phosphorus chemical shifts as well as measurements of T1 relaxation times at different temperatures allowed us to propose several structures for the complexes formed by (Tp)4(CH2)5Acr with its complementary sequence.