Fig. 2

a-b, Overview of the dormant ribosome structure from 1 hpf zebrafish (a) and Xenopus egg (b). Ribosome-associated factors are shown as surface representations; eEF2b and eIF5a correspond to PDB-6MTE¹⁸ and PDB-5DAT. c, Density maps (in mesh) of the two modules of the Xenopus dormant ribosome. d, Habp4 and eEF2b (6MTE¹⁸) are shown as surface representations in the zebrafish dormant ribosome (left). A rabbit ribosome stalled on an mRNA (6HCF⁵⁹) is shown for comparison (right). e, Clipping of the zebrafish dormant ribosome shows eIF5a (5DAT) and Dap1b bound within the polypeptide exit tunnel (left). The structure of a stalled human ribosome (6OLE⁶⁰) containing a nascent polypeptide chain (NPC) and a P/E-tRNA is shown for comparison (right). f, Comparison of the peptidyl-transferase center of a rabbit 80S ribosome stalled with a poly-Lysine NPC and a P/E-tRNA (6SGC⁶¹, left) and of the Xenopus dormant ribosome (middle). For comparison, the P/E-tRNA (6SGC⁶¹), absent in dormant ribosomes, was superimposed onto the Xenopus egg ribosome (right; eIF5A is hidden). Critical amino acids and 28S rRNA nucleotides are labeled; interactions are depicted with dashed lines. Boxed areas are shown at higher magnification in g. g, A3073 of Xenopus 28S rRNA (bottom; equivalent to A3908 of rabbit 28S, top) displays a different conformation when interacting with Gln108 of Dapl1. h, Distribution of ribosomal particles among the classes obtained with cryoDRGN⁴⁸. Representative filtered maps of the major classes are shown (Extended Data Fig. 3g, h; Supplementary Table 3; n.a refers to “non-assigned” particles). Ct, C-terminus.