Three-dimensional structure of a pre-catalytic human spliceosomal complex B

Publisher Website
Google Scholar
Abstract
Major structural changes occur in the spliceosome during its transition from the fully assembled complex B to the catalytically activated spliceosome. To understand the rearrangement, it is necessary to know the detailed three-dimensional structures of these complexes. Here, we have immunoaffinity-purified human spliceosomes (designated BΔU1) at a stage after U4/U6·U5 tri-snRNP integration but before activation, and have determined the three-dimensional structure of BΔU1 by single-particle electron cryomicroscopy at a resolution of ∼40 Å. The overall size of the complex is about 370 × 270 × 170 Å. The three-dimensional structure features a roughly triangular body linked to a head domain in variable orientations. The body is very similar in size and shape to the isolated U4/U6·U5 tri-snRNP. This provides initial insight into the structural organization of complex B.