Sequence-targeted photosensitized reactions in nucleic acids by oligo-alpha-deoxynucleotides and...

Proflavin was covalently linked to the 3'-end or to the 5'-end of an octadeoxythymidylate. This oligonucleotide was synthesized with either the natural beta-anomer of thymidine or its synthetic alpha-anomer. A polymethylene chain was used to link one of the amino groups of proflavin to a terminal thiophosphate group of the oligonucleotide. A 27-mer oligodeoxynucleotide containing an octadeoxyadenylate sequence was used as a target for the proflavin-substituted octadeoxythymidylates. Upon irradiation with visible light, photo-cross-linking reactions induced the formation of branched species that migrated more slowly than the 27-mer on denaturing polyacrylamide gels. Piperidine treatment of the photo-cross-linked species induced strand breaks in the 27-mer. In addition, proflavin induced photosensitized reactions at guanine residues in the 27-mer sequence which were converted to strand breaks following piperidine treatment. Triple-helix formation by the oligothymidylates with their complementary oligodeoxyadenylate sequence at high salt concentration led to photo-cross-linking and cleavage reactions on both sides of the target sequence. These results show that it is possible to target photosensitized reactions to specific sequences on nucleic acids. This opens new possibilities for site-directed mutagenesis and the development of photoactive anti-messenger oligodeoxynucleotides.