A fluorescent radioiodinated oligonucleotidic photoaffinity probe for protein labeling: Synthesis and photolabeling of thrombin

To study the interactions between oligonucleotides and proteins, an origina l photoaffinity radiolabeling probe has been synthesized. Starting with a 5 '-pyridyldithio-3'-amino-oligonucleotide, the photophore benzophenone was f irst coupled to the 3' end, through acylation by an activated ester of benz oylbenzoic acid. A fluorescein molecule was grafted by alkylation of the fr ee 5'-SH. This compound was finally radiolabeled with I-125 using IodoBeads . The selective photolabeling of thrombin in a complex protein mixture by t he radioiodinated probe validates this strategy to identify oligonucleotide -binding proteins.