title: Three-dimensional structure of the native spliceosome by cryo-electron microscopy.
abstract: Splicing of pre-mRNA occurs in a multicomponent macromolecular machine--the spliceosome. The spliceosome can be assembled in vitro by a stepwise assembly of a number of snRNPs and additional proteins on exogenously added pre-mRNA. In contrast, splicing in vivo occurs in preformed particles where endogenous pre-mRNAs are packaged with all five spliceosomal U snRNPs (penta-snRNP) together with other splicing factors. Here we present a three-dimensional image reconstruction by cryo-electron microscopy of native spliceosomes, derived from cell nuclei, at a resolution of 20 angstroms. The structure revealed an elongated globular particle made up of two distinct subunits connected to each other leaving a tunnel in between. We show here that the larger subunit is a suitable candidate to accommodate the penta-snRNP, and that the tunnel could accommodate the pre-mRNA component of the spliceosome. The features this structure reveals provide new insight into the global architecture of the native splicing machine.
authors.affiliation: Department of Genetics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
authors.forename: Maia
authors.initials: M
authors.lastname: Azubel
authors.forename: Sharon G
authors.initials: SG
authors.lastname: Wolf
authors.forename: Joseph
authors.initials: J
authors.lastname: Sperling
authors.forename: Ruth
authors.initials: R
authors.lastname: Sperling
mesh_terms: D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure*; D020285:Cryoelectron Microscopy; D006367:HeLa Cells; D006801:Humans; D046911:Macromolecular Substances; D008958:Models, Molecular; D015394:Molecular Structure; D012322:RNA Precursors / Q000235:genetics / Q000378:metabolism; D012326:RNA Splicing / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis* / Q000235:genetics; D017411:Ribonucleoproteins, Small Nuclear / Q000235:genetics / Q000378:metabolism; D017381:Spliceosomes / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure*
chemical_list: D046911:Macromolecular Substances; D012322:RNA Precursors; D012333:RNA, Messenger; D017411:Ribonucleoproteins, Small Nuclear