Spectroscopic studies on the formation and thermal stability of DNA triplexes with a benzoannulated delta-carboline-oligonucleotide conjugate

A benzoannulated delta-carboline with a phenyl substituent has been covalently tethered to the 3'-end of a triplex-forming oligonucleotide and its ability to bind and stabilize DNA triple helices has been examined by various spectroscopic methods. UV thermal melting experiments were conducted with different hairpin duplexes and with a complementary single-stranded oligonucleotide as targets for the conjugate. The delta-carboline ligand preferentially binds triplexes over duplexes and leads to a temperature increase of the triplex-to-duplex transition by up to 23 degrees C. The results obtained from UV, CD and fluorescence measurements suggest that the delta-carboline ligand exhibits specific interactions with a triplex and favors binding by intercalation at the triplex-duplex junction.