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 Mr 80 K known to be RNase L. Radiobinding and core‐cellulose assays as well as photoaffinity labelling experiments with 16 are described.