A human postcatalytic spliceosome structure reveals essential roles of metazoan factors for exon ligation

DOI: 10.1126/science.aaw5569
PMID: 30705154

Authors: Sebastian M. Fica (MRC Laboratory of Molecular Biology) , Chris Oubridge (MRC Laboratory of Molecular Biology) , Max E. Wilkinson (MRC Laboratory of Molecular Biology) , Andrew J. Newman (MRC Laboratory of Molecular Biology) , Kiyoshi Nagai (MRC Laboratory of Molecular Biology)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Science , VOL 363 , PAGES 710 - 714

State: Published (Approved)
Published: February 2019
Diamond Proposal Number(s): 17434

Abstract: During exon ligation, the Saccharomyces cerevisiae spliceosome recognizes the 3'-splice site (3'SS) of precursor messenger RNA (pre-mRNA) through non-Watson-Crick pairing with the 5'SS and the branch adenosine, in a conformation stabilized by Prp18 and Prp8. Here we present the 3.3-angstrom cryo-electron microscopy structure of a human postcatalytic spliceosome just after exon ligation. The 3'SS docks at the active site through conserved RNA interactions in the absence of Prp18. Unexpectedly, the metazoan-specific FAM32A directly bridges the 5'-exon and intron 3'SS of pre-mRNA and promotes exon ligation, as shown by functional assays. CACTIN, SDE2, and NKAP-factors implicated in alternative splicing-further stabilize the catalytic conformation of the spliceosome during exon ligation. Together these four proteins act as exon ligation factors. Our study reveals how the human spliceosome has co-opted additional proteins to modulate a conserved RNA-based mechanism for 3'SS selection and to potentially fine-tune alternative splicing at the exon ligation stage.

Journal Keywords: cryoEM; splicing; gene expression

Subject Areas: Biology and Bio-materials, Chemistry, Medicine

Diamond Offline Facilities: Electron Bio-Imaging Centre (eBIC)
Instruments: Krios II-Titan Krios II at Diamond