title: 3D cryo-EM structure of an active step I spliceosome and localization of its catalytic core.
abstract: The spliceosome excises introns from pre-mRNA in a two-step splicing reaction. So far, the three-dimensional (3D) structure of a spliceosome with preserved catalytic activity has remained elusive. Here, we determined the 3D structure of the human, catalytically active step I spliceosome (C complex) by cryo-electron microscopy (cryo-EM) in vitrified ice. Via immunolabeling we mapped the position of the 5' exon. The C complex contains an unusually salt-stable ribonucleoprotein (RNP) core that harbors its catalytic center. We determined the 3D structure of this RNP core and also that of a post-step II particle, the 35S U5 snRNP, which contains most of the C complex core proteins. As C complex domains could be recognized in these structures, their position in the C complex could be determined, thereby allowing the region harboring the spliceosome's catalytic core to be localized.
authors.affiliation: Research Group of 3D Electron Cryomicroscopy, Max Planck Institute for Biophysical Chemistry, D-37077 Göttingen, Germany.
authors.forename: Monika M
authors.initials: MM
authors.lastname: Golas
authors.forename: Bjoern
authors.initials: B
authors.lastname: Sander
authors.forename: Sergey
authors.initials: S
authors.lastname: Bessonov
authors.forename: Michael
authors.initials: M
authors.lastname: Grote
authors.forename: Elmar
authors.initials: E
authors.lastname: Wolf
authors.forename: Berthold
authors.initials: B
authors.lastname: Kastner
authors.forename: Holger
authors.initials: H
authors.lastname: Stark
authors.forename: Reinhard
authors.initials: R
authors.lastname: Lührmann
mesh_terms: D055162:Biocatalysis; D020134:Catalytic Domain; D020285:Cryoelectron Microscopy; D006801:Humans; D008958:Models, Molecular; D017381:Spliceosomes / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure*