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{{Large structure}}
==The overall structure of the yeast spliceosomal U4/U6.U5 tri-snRNP at 3.7 Angstrom==
==The overall structure of the yeast spliceosomal U4/U6.U5 tri-snRNP at 3.7 Angstrom==
<StructureSection load='5gan' size='340' side='right' caption='[[5gan]], [[Resolution|resolution]] 3.60&Aring;' scene=''>
<StructureSection load='5gan' size='340' side='right' caption='[[5gan]], [[Resolution|resolution]] 3.60&Aring;' scene=''>
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<div style="background-color:#fffaf0;">
<div style="background-color:#fffaf0;">
== Publication Abstract from PubMed ==
== Publication Abstract from PubMed ==
U4/U6.U5 tri-snRNP is a 1.5-megadalton pre-assembled spliceosomal complex comprising U5 small nuclear RNA (snRNA), extensively base-paired U4/U6 snRNAs and more than 30 proteins, including the key components Prp8, Brr2 and Snu114. The tri-snRNP combines with a precursor messenger RNA substrate bound to U1 and U2 small nuclear ribonucleoprotein particles (snRNPs), and transforms into a catalytically active spliceosome after extensive compositional and conformational changes triggered by unwinding of the U4 and U6 (U4/U6) snRNAs. Here we use cryo-electron microscopy single-particle reconstruction of Saccharomyces cerevisiae tri-snRNP at 5.9 A resolution to reveal the essentially complete organization of its RNA and protein components. The single-stranded region of U4 snRNA between its 3' stem-loop and the U4/U6 snRNA stem I is loaded into the Brr2 helicase active site ready for unwinding. Snu114 and the amino-terminal domain of Prp8 position U5 snRNA to insert its loop I, which aligns the exons for splicing, into the Prp8 active site cavity. The structure provides crucial insights into the activation process and the active site of the spliceosome.
U4/U6.U5 tri-snRNP represents a substantial part of the spliceosome before activation. A cryo-electron microscopy structure of Saccharomyces cerevisiae U4/U6.U5 tri-snRNP at 3.7 A resolution led to an essentially complete atomic model comprising 30 proteins plus U4/U6 and U5 small nuclear RNAs (snRNAs). The structure reveals striking interweaving interactions of the protein and RNA components, including extended polypeptides penetrating into subunit interfaces. The invariant ACAGAGA sequence of U6 snRNA, which base-pairs with the 5'-splice site during catalytic activation, forms a hairpin stabilized by Dib1 and Prp8 while the adjacent nucleotides interact with the exon binding loop 1 of U5 snRNA. Snu114 harbours GTP, but its putative catalytic histidine is held away from the gamma-phosphate by hydrogen bonding to a tyrosine in the amino-terminal domain of Prp8. Mutation of this histidine to alanine has no detectable effect on yeast growth. The structure provides important new insights into the spliceosome activation process leading to the formation of the catalytic centre.


The architecture of the spliceosomal U4/U6.U5 tri-snRNP.,Nguyen TH, Galej WP, Bai XC, Savva CG, Newman AJ, Scheres SH, Nagai K Nature. 2015 Jul 2;523(7558):47-52. doi: 10.1038/nature14548. Epub 2015 Jun 24. PMID:26106855<ref>PMID:26106855</ref>
Cryo-EM structure of the yeast U4/U6.U5 tri-snRNP at 3.7 A resolution.,Nguyen TH, Galej WP, Bai XC, Oubridge C, Newman AJ, Scheres SH, Nagai K Nature. 2016 Feb 18;530(7590):298-302. doi: 10.1038/nature16940. Epub 2016 Feb 1. PMID:26829225<ref>PMID:26829225</ref>


From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
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