SITE-SPECIFIC PHOTOMODIFICATION OF NUCLEI C-ACIDS BY ARYLAZIDE AND PERFLUOROARYLAZIDE DERIVATIVES OF OLIGONUCLEOTIDES .3. OLIGONUCLEOTIDE REAGENTS WITH A TERMINAL OR INTERNAL PHOTOACTIVE GROUP

Photomodification of target oligonucleotides with reagents bearing p-a zidotetrafluorobenzamide group at various positions of the oligonucleo tide address was investigated. The photoactive group was attached to t he 5'- or 3'-terminal phosphate or at the C5-position of a deoxyuridin e residue at the 5'-end or inside the oligonucleotide chain. The reage nts with the internal photoactive group modified the target with 50-55 % efficiency (fraction of covalent adducts reagent-target), whereas th e derivatives with a terminal reactive group were more effective (70%) . The main point of the modification was the guanosine residue of the target which located near to the photoactive group and was not involve d into the duplex formation. Tandems of reagents which are complementa ry to neighbouring sites of the target modify predominantly the same g uanosine residue, with up to 80% extent.