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

Publication date: Available online 3 August 2017
Source:Cell
Author(s): Karl Bertram, Dmitry E. Agafonov, Olexandr Dybkov, David Haselbach, Majety N. Leelaram, Cindy L. Will, Henning Urlaub, Berthold Kastner, Reinhard Lührmann, Holger Stark
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.

Graphical abstract

Teaser

Structure of the human spliceosome getting ready for action.


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