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Cell. 2017 Aug 10;170(4):701-713.e11. doi: 10.1016/j.cell.2017.07.011. Epub 2017 Aug 3.

Cryo-EM Structure of a Pre-catalytic Human Spliceosome Primed for Activation.

Author information

1
Department of Structural Dynamics, MPI for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany.
2
Department of Cellular Biochemistry, MPI for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany.
3
Bioanalytical Mass Spectrometry, MPI for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany; Bioanalytics Group, Institute for Clinical Chemistry, University Medical Center Göttingen, Robert-Koch-Straße 40, 37075 Göttingen, Germany.
4
Department of Cellular Biochemistry, MPI for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany. Electronic address: b.kastner@mpibpc.mpg.de.
5
Department of Cellular Biochemistry, MPI for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany. Electronic address: reinhard.luehrmann@mpibpc.mpg.de.
6
Department of Structural Dynamics, MPI for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany. Electronic address: hstark1@gwdg.de.

Abstract

Little is known about the spliceosome's structure before its extensive remodeling into a catalytically active complex. Here, we report a 3D cryo-EM structure of a pre-catalytic human spliceosomal B complex. The U2 snRNP-containing head domain is connected to the B complex main body via three main bridges. U4/U6.U5 tri-snRNP proteins, which are located in the main body, undergo significant rearrangements during tri-snRNP integration into the B complex. These include formation of a partially closed Prp8 conformation that creates, together with Dim1, a 5' splice site (ss) binding pocket, displacement of Sad1, and rearrangement of Brr2 such that it contacts its U4/U6 substrate and is poised for the subsequent spliceosome activation step. The molecular organization of several B-specific proteins suggests that they are involved in negatively regulating Brr2, positioning the U6/5'ss helix, and stabilizing the B complex structure. Our results indicate significant differences between the early activation phase of human and yeast spliceosomes.

KEYWORDS:

B complex spliceosome; B-specific proteins; cryo-EM; pre-catalytic spliceosome; pre-mRNA splicing; spliceosome; spliceosome structure

PMID:
28781166
DOI:
10.1016/j.cell.2017.07.011
[Indexed for MEDLINE]
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