Fig. 1: Cryo-EM structure of the J-K-St/eIF4G^HEAT1/eIF4A complex.

a Schematic representation of the translation initiation complex formed by EMCV IRES. The J-K-St region directly interacts with the scaffolding protein eIF4G of the host cell, leading to the recruitments of eIF4A, eIF3, eIF2, and the ribosomal 40S subunit to the initiation codon. This figure is adapted from ref. ⁹. b Domain organization of the full-length eIF4G and the eIF4G^HEAT1 construct. c NMR structure of J-K-St in the free-state⁹ (PDB ID: 2NBX). d Overall structure of the J-K-St/eIF4G^HEAT1/eIF4A ternary complex, overlaid with the lowpass-filtered cryo-EM density map. e Focused cryo-EM map (left) and the structure (right) of J-K-St/eIF4G^HEAT1. The J, K, and St domains of J-K-St are labeled along with the A_SL domain at the junction. Mg²⁺ ions are shown as black spheres. f, g Electrostatic potential representations of the surface of eIF4G^HEAT1 at the interface between the J domain (f) and the St domain (g), contoured from –5 kT/e (red) to +5 kT/e (blue). The residues of the J-K-St in contact with the eIF4G^HEAT1 are shown as sticks. The labels of the extruded residues, A724 on the J domain (f) and G777 on the St domain (g), are highlighted with boxes. h Comparison of the domain orientations. The structures of J-K-St in the free-state and in complex with eIF4G^HEAT1/eIF4A are shown as surface and ribbon-and-stick representations, respectively. The J, K, St, and A_SL domains are colored green, blue, orange, and red, respectively. The structures are aligned with the K domain, and changes in the J and St domain orientations upon complex formations are shown as black arrows.