Nucleotides part XXX Chemical synthesis of adenylyl-(2′ → 5′)-adenylyl-(2′ → 5′)-8-azidoadenosine,and activation and photoaffinity labelling of RNase L by [32P]p5′A2′p5′A2′p5′N38A

The chemical synthesis of adenylyl-(2′–5′)-adenylyl-(2′–5′)-8-azidoadenosine ( 15 ) was performed by the phosphotriester approach. Enzymatic phosphorylation of 15 by γ-³²P]ATP led to the corresponding labelled 5′-monophosphate 16 . Photoinsertion of 16 took place on UV irradiation by covalent cross linking to a protein of M_r 80 K known to be RNase L. Radiobinding and core-cellulose assays as well as photoaffinity labelling experiments with 16 are described.