Figure 4.

Structure of the PKR RBD (amino acids 1–179) showing the three amino acids selected for mutagenesis along with the structure of the photocrosslinking reagent TFPAM-3 used to modify the different cysteine residues. Using Chem3D (CambridgeSoft), the distance between the reactive maleimide carbon and the putative nitrene was estimated to be ~11 Å. The protein structure shown was generated using Insight II (Biosym) running on a Silicon Graphics O₂ workstation and coordinates kindly provided by Qin and co-workers (Lerner Research Institute, The Cleveland Clinic Foundation, Cleveland, OH) (16).