Calviño, FabiolaKornprobst, MarkusSchermann, GezaBirkle, FabienneWild, KlemensFischer, TamasHurt, EdAhmed, YasarSinning, Irmgard2021-09-212021-09-211932-6203http://hdl.handle.net/1885/248296Eukaryotic ribosome biogenesis begins with the co-transcriptional assembly of the 90S pre-ribosome. The ‘U three protein’ (UTP) complexes and snoRNP particles arrange around the nascent pre-ribosomal RNA chaperoning its folding and further maturation. The earliest event in this hierarchical process is the binding of the UTP-A complex to the 5'-end of the pre-ribosomal RNA (5'-ETS). This oligomeric complex predominantly consists of β-propeller and α-solenoidal proteins. Here we present the structure of the Utp4 subunit from the thermophilic fungus Chaetomium thermophilum at 2.15 Å resolution and analyze its function by UV RNA-crosslinking (CRAC) and in context of a recent cryo-EM structure of the 90S pre-ribosome. Utp4 consists of two orthogonal and highly basic β-propellers that perfectly fit the EM-data. The Utp4 structure highlights an unusual Velcro-closure of its C-terminal β-propeller as relevant for protein integrity and potentially Utp8 recognition in the context of the pre-ribosome. We provide a first model of the 5'-ETS RNA from the internally hidden 5'-end up to the region that hybridizes to the 3'-hinge sequence of U3 snoRNA and validate a specific Utp4/5'-ETS interaction by CRAC analysis.This work was supported by Deutsche Forschungsgemeinschaft (DFG) (SFB638, Z4 to I. S. and HU363/15-1 to E.H. and the Leibniz programme to I.S.); Cluster of Excellence CellNetworks (EcTOP1 to I.S. and E.H.); Funding for open access charge: DFG [Leibniz Programme]. M.K. was funded by a Kekule Fellowship (VCI).application/pdfen-AU© 2017 Calvin˜o et al.https://creativecommons.org/licenses/by/4.0/201710.1371/journal.pone.01787522020-11-23Creative Commons Attribution License