biostudies-literatureUnknownPanwar HSNIGMS NIH HHSH/ACA small nucleolar ribonucleoproteins (H/ACA snoRNPs) facilitate essential cellular processes such as RNA modification, folding, and stability. Here, we present multiple cryo-EM structures of endogenous, catalytically active insect H/ACA snoRNPs containing two protomers assembled on a two-hairpin H/ACA snoRNA. By characterizing key protein-protein and protein-RNA interactions, we reveal the coordination of pseudouridylation activity across the two protomers which explains the predominance of two-hairpin structures in eukaryotic H/ACA snoRNAs. Moreover, we discovered that several mutations in H/ACA proteins associated with Dyskeratosis congenita directly impair pseudouridine formation suggesting how these mutations disrupt RNA modification and ribosome biogenesis in this disease. AdditiobioRxiv : the preprint server for biology2025.06.07.658439https://www.ebi.ac.uk/biostudies/studies/S-EPMC12157440biostudies-literatureInterprotomer Communication and Functional Asymmetry in H/ACA snoRNPs.PMC12157440R35 GM147261Kothe UXie XSheldon RLee HJang HSWorden EVos TJPanwar HSfalseInterprotomer Communication and Functional Asymmetry in H/ACA snoRNPs.H/ACA small nucleolar ribonucleoproteins (H/ACA snoRNPs) facilitate essential cellular processes such as RNA modification, folding, and stability. Here, we present multiple cryo-EM structures of endogenous, catalytically active insect H/ACA snoRNPs containing two protomers assembled on a two-hairpin H/ACA snoRNA. By characterizing key protein-protein and protein-RNA interactions, we reveal the coordination of pseudouridylation activity across the two protomers which explains the predominance of two-hairpin structures in eukaryotic H/ACA snoRNAs. Moreover, we discovered that several mutations in H/ACA proteins associated with Dyskeratosis congenita directly impair pseudouridine formation suggesting how these mutations disrupt RNA modification and ribosome biogenesis in this disease. Additio2025-01-01T00:00:00Z2025 Jun2026-04-08T19:34:18.35Z2026-04-08T13:59:10.933ZS-EPMC121574404050155310.1101/2025.06.07.658439