Sensitized DNA photomodification by binary systems of oligonucleotide conjugates. V. The target DNA sequence effect and the quantitative photomodification

A sensitized photomodification of several single-stranded target DNAs by bi nary systems of oligonucleotide conjugates complementary to the adjacent re gions of DNA was performed. One of the conjugates contained a sensitizer (p yrene, anthracene, or 1,2-benzanthracene), and another conjugate contained a photoreagent 4-azidotetrafluorobenzalhydrazone. The sensitized photomodif ication is initiated by irradiation at 365-580 nm due to effective energy t ransfer from the excited sensitizer to the photoreagent in a complementary complex of the binary system with the target DNA where the sensitizer and p hotoreagent are brought sterically together. Conditions for the quantitativ e photomodification of a single-stranded DNA by the binary system of oligon ucleotide conjugates were found. The maximum degree of photomodification de pends on the number of guanosine residues in the (pG)(n) sequence of the ta rget DNA at the modification site: at n = 1 the yield of covalent adducts w as 62-68%, at n = 2, 75-82%, and at n = 4, 98-99%.