Molecular architecture of the human U4/U6.U5 tri-snRNP
Dmitry E. Agafonov1,*, Berthold Kastner1,*, Olexandr Dybkov1,*, Romina V. Hofele2,3,†, Wen-Ti Liu4,5, Henning Urlaub2,3,‡, Reinhard Lührmann1,‡, Holger Stark4,5,‡
- Author Affiliations
1Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, D-37077 Göttingen, Germany.
2Bioanalytical Mass Spectrometry, Max Planck Institute for Biophysical Chemistry, D-37077 Göttingen, Germany.
3Bioanalytics Group, Institute for Clinical Chemistry, University Medical Center Göttingen, D-37075 Göttingen, Germany.
4Department of 3D Electron Cryomicroscopy, Georg-August Universität Göttingen, D-37077 Göttingen, Germany.
5Department of Structural Dynamics, Max Planck Institute for Biophysical Chemistry, D-37077 Göttingen, Germany.
↵‡Corresponding author. E-mail: firstname.lastname@example.org (R.L.); email@example.com (H.S.); firstname.lastname@example.org (H.U.)
↵* These authors contributed equally to this work.
↵† Present address: Medimmune, Gaithersburg, MD, USA.
Science 25 Mar 2016:
Vol. 351, Issue 6280, pp. 1416-1420
A human spliceosomal subcomplex
The spliceosome is an RNA and protein molecular machine that cuts out introns from messenger RNAs. Agafonov et al. used cryo-electron microscopy to determine the structure of the largest intermediate subcomplex on the assembly pathway for the human spliceosome (see the Perspective by Cate). The structure shows substantial differences from the equivalent yeast complex. It also reveals how the subcomplex must dock onto the rest of the spliceosome and hints at the structural changes the complex must go through to form the mature spliceosome.
The U4/U6.U5 triple small nuclear ribonucleoprotein (tri-snRNP) is a major spliceosome building block. We obtained a three-dimensional structure of the 1.8-megadalton human tri-snRNP at a resolution of 7 angstroms using single-particle cryo–electron microscopy (cryo-EM). We fit all known high-resolution structures of tri-snRNP components into the EM density map and validated them by protein cross-linking. Our model reveals how the spatial organization of Brr2 RNA helicase prevents premature U4/U6 RNA unwinding in isolated human tri-snRNPs and how the ubiquitin C-terminal hydrolase–like protein Sad1 likely tethers the helicase Brr2 to its preactivation position. Comparison of our model with cryo-EM three-dimensional structures of the Saccharomyces cerevisiae tri-snRNP and Schizosaccharomyces pombe spliceosome indicates that Brr2 undergoes a marked conformational change during spliceosome activation, and that the scaffolding protein Prp8 is also rearranged to accommodate the spliceosome’s catalytic RNA network.
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