Ru-labeled oligonucleotides for photoinduced reactions on targeted DNA guanines

As a strategy to synthesize new sequence-specific DNA photoreagents, oligod eoxyribonucleotides bearing a photoreactive [Ru-II(tap)(2)(dip)](2+) comple x (tap = 1,4,5,8-tetraazaphenanthrene: dip = 4,7-diphenylphenanthroline) te thered to a central nucleotide base have been prepared and characterized. T he resulting Ru-labeled oligonucleotides exhibit absorption and emission pr operties of the tethered metal complex and bind to complementary single-str anded DNA sequences. The thermal denaturation curves are not significantly affected by the chemical attachment of the complex. Steady-state and time-r esolved emission data reveal a significant luminescence quenching upon hybr idization of the Ru-labeled oligonucleotide with the complementary target s trand, if the strand contains guanines. Based on the behavior of the free c omplex, the quenching process is attributed to a photoinduced electron tran sfer from the guanines of the target strand. This primary process is relate d to the formation of photoproduct(s) on the duplex that generate an irreve rsible photocrosslinking of the two strands. This work constitutes an initi al step in the design of sequence-specific photocrosslinking agents.