Journal Article

Prespliceosome structure provides insights into spliceosome assembly and regulation

Plaschka, Clemens, Lin, Pei-Chun, Charenton, Clément, Nagai, Kiyoshi

2018

Overview

The spliceosome catalyses the excision of introns from pre-mRNA in two steps, branching and exon ligation, and is assembled from five small nuclear ribonucleoprotein particles (snRNPs; U1, U2, U4, U5, U6) and numerous non-snRNP factors 1 . For branching, the intron 5′ splice site and the branch point sequence are selected and brought by the U1 and U2 snRNPs into the prespliceosome 1 , which is a focal point for regulation by alternative splicing factors 2 . The U4/U6.U5 tri-snRNP subsequently joins the prespliceosome to form the complete pre-catalytic spliceosome. Recent studies have revealed the structural basis of the branching and exon-ligation reactions 3 , however, the structural basis of the early events in spliceosome assembly remains poorly understood 4 . Here we report the cryo-electron microscopy structure of the yeast Saccharomyces cerevisiae prespliceosome at near-atomic resolution. The structure reveals an induced stabilization of the 5′ splice site in the U1 snRNP, and provides structural insights into the functions of the human alternative splicing factors LUC7-like (yeast Luc7) and TIA-1 (yeast Nam8), both of which have been linked to human disease 5 , 6 . In the prespliceosome, the U1 snRNP associates with the U2 snRNP through a stable contact with the U2 3′ domain and a transient yeast-specific contact with the U2 SF3b-containing 5′ region, leaving its tri-snRNP-binding interface fully exposed. The results suggest mechanisms for 5′ splice site transfer to the U6 ACAGAGA region within the assembled spliceosome and for its subsequent conversion to the activation-competent B-complex spliceosome 7 , 8 . Taken together, the data provide a working model to investigate the early steps of spliceosome assembly. The cryo-electron microscopy structure of the Saccharomyces cerevisiae prespliceosome provides insights into splice-site selection and early spliceosome assembly events.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 101/28 / 631/337/1645/1792 / 631/337/1645/1946 / 631/535/1258/1259 / 64 / 82 / 82/58 / Adenosine / Alternative splicing / Alternative Splicing - genetics / Assembly / Atomic structure / Atoms / Baking yeast / Catalysis / Cell cycle / Cryoelectron Microscopy / Crystal structure / Electron microscopy / Humanities and Social Sciences / Introns / Letter / Messenger RNA / Microscopy / Models, Molecular / mRNA / multidisciplinary / Nuclear reactions / Physiological aspects / Properties / Proteins / Ribonucleoprotein, U1 Small Nuclear - chemistry / Ribonucleoprotein, U1 Small Nuclear - metabolism / Ribonucleoprotein, U1 Small Nuclear - ultrastructure / Ribonucleoprotein, U2 Small Nuclear - chemistry / Ribonucleoprotein, U2 Small Nuclear - metabolism / Ribonucleoprotein, U4-U6 Small Nuclear - chemistry / Ribonucleoprotein, U4-U6 Small Nuclear - metabolism / Ribonucleoproteins (small nuclear) / Ribonucleoproteins (U2 small nuclear) / Ribonucleoproteins, Small Nuclear - metabolism / RNA / RNA Splice Sites / RNA Splicing Factors - metabolism / Saccharomyces cerevisiae / Saccharomyces cerevisiae - ultrastructure / Saccharomyces cerevisiae Proteins - metabolism / Science / Science (multidisciplinary) / Spliceosomes / Spliceosomes - chemistry / Spliceosomes - metabolism / Spliceosomes - ultrastructure / Splicing / Splicing factors / Structure / Yeast