Figure 2.

X-ray structures of β-phosphorothio(/seleno)ate mRNA 5′ cap analogs in complexes with eukaryotic translation initiation factor 4E. (A) Structures of β-S-ARCAs and m⁷GpppG (PDB ID: 1L8B) in complexes with eIF4E—simulated annealing omit maps (green mesh) are contoured at 3.0 σ; the electron density corresponding to the first transcribed nucleotide (TSS) is not visible in any of these structures. (B) Structures of β-selenophosphate cap analogs in complexes with eIF4E—anomalous maps (purple mesh) are contoured at 5.0 σ. (C) Resonance structures of disubstituted phosphate and phosphorothioate residues.