9XA9

Cryo-EM structure of the pre-40S ribosome (Enp1-Rrp12 WT) from Chaetomium thermophilum, state Tsr1-1

Summary for 9XA9

• Entry DOI: 10.2210/pdb9xa9/pdb
• EMDB information: 66679
• Descriptor: Small ribosomal subunit protein uS2, 40S ribosomal protein S13-like protein, 40S ribosomal protein S14-like protein, ... (23 entities in total)
• Functional Keywords: 90s, pre-40s ribosome, rrp12, enp1, ribosome biogenesis, ribosome
• Biological source: Thermochaetoides thermophila; More
• Total number of polymer chains: 20
• Total formula weight: 963673.21

Authors

Lau, B.,Li, Y.,Zhu, J.,Fischer, P.,Hong, X.,Yuan, R.,Beckmann, R.,Hurt, E.,Cheng, J. (deposition date: 2025-10-22, release date: 2026-06-24)

Primary citation

Lau, B.,Li, Y.,Zhu, J.,Ye, X.,Fischer, P.,Hong, X.,Yuan, R.,Beckmann, R.,Hurt, E.,Cheng, J.
Nucleoplasmic checkpoint of the 40S ribosomal decoding center maturation.
Cell Rep, 45:117545-117545, 2026

PubMed Abstract: The decoding center (DC) is a key ribosomal structure for accurate translation, assembled in a multi-step process that starts on nucleolar pre-ribosomes and ends in the cytoplasm. While late cytoplasmic steps and their checkpoint mechanisms are well characterized, the regulation of early nucleoplasmic DC assembly is unclear. Here, we show that the essential assembly factor Rrp12 plays a central coordinating role. Using Chaetomium thermophilum and cryo-electron microscopy analyses of fifteen pre-40S intermediates, we demonstrate that Rrp12 C terminus truncation: (1) inhibits release of the Utp14-Dhr1 pair, (2) displaces Tsr1, (3) promotes premature stabilization of h28, and (4) prevents h44 formation. These defects impair final 18S rRNA processing and prematurely activate the quality control kinase Rio1. Our results reveal a nucleoplasmic checkpoint during DC formation and establish Rrp12 as a critical regulator ensuring accurate assembly and orderly ribosome maturation.

PubMed: 42275223
DOI: 10.1016/j.celrep.2026.117545

Experimental method

ELECTRON MICROSCOPY (3.3 Å)