Spliceosome Structure and Function

Abstract

SUMMARYPre-mRNA splicing is catalyzed by the spliceosome, a multimegadalton ribonucleoprotein (RNP) complex comprised of five snRNPs and numerous proteins. Intricate RNA-RNA and RNP networks, which serve to align the reactive groups of the pre-mRNA for catalysis, are formed and repeatedly rearranged during spliceosome assembly and catalysis. Both the conformation and composition of the spliceosome are highly dynamic, affording the splicing machinery its accuracy and flexibility, and these remarkable dynamics are largely conserved between yeast and metazoans. Because of its dynamic and complex nature, obtaining structural information about the spliceosome represents a major challenge. Electron microscopy has revealed the general morphology of several spliceosomal complexes and their snRNP subunits, and also the spatial arrangement of some of their components. X-ray and NMR studies have provided high resolution structure information about spliceosomal proteins alone or complexed with one or more binding partners. The extensive interplay of RNA and proteins in aligning the pre-mRNA's reactive groups, and the presence of both RNA and protein at the core of the splicing machinery, suggest that the spliceosome is an RNP enzyme. However, elucidation of the precise nature of the spliceosome's active site, awaits the generation of a high-resolution structure of its RNP core.

Pseudouridines in spliceosomal snRNAs

“…Instead, it is first transcribed in the form of pre-mRNA, composed of both coding exons and non-coding introns (Berget et al, 1977;Chow et al, 1977). Therefore, before it is shipped to the cytoplasm to direct protein synthesis, a chemical reaction, termed splicing, must take place to excise the introns and join the exons into a mature mRNA (Staley and Guthrie, 1998;Burge et al, 1999;Yu et al, 1999;Karijolich and Yu, 2008;Will and Lührmann, 2011).…”

“…Splicing is catalyzed by the spliceosome, a large, dynamic RNA-protein complex that takes on various forms through the different steps of splicing (Konarska and Sharp, 1986;Cheng and Abelson, 1987;Nilsen, 1994;Burge et al, 1999;Yu et al, 1999;Karijolich and Yu, 2008;Will and Lührmann, 2011). Spliceosome activity depends on a large number of protein components, as well as five "uridyl-rich" snRNAs-U1, U2, U4, U5, and U6.…”

L’épissage des ARN pré-messagers : quand le splicéosome perd pied

“…Il est assuré par un complexe de plus de 200 protéines associées ou non à des petites ribonucléoprotéines, les snRNP (small nuclear ribonucleoprotein) U1, U2, U4/U6 et U5 [1]. Le macro-complexe ainsi formé, le splicéosome, assure l'excision des introns et la ligature des exons, en un cycle bien caractérisé faisant intervenir deux réactions consécutives de trans-estérification ( Figure 1A).…”

Analyzing the Protein Assembly and Dynamics of the Human Spliceosome with SILAC

“…Complete pre-mRNA splicing in higher eukaryotes hence requires several processes: (1) the ordered assembly of the U snRNPs on the pre-mRNA in concert with the recruitment of additional non-snRNP splicing factors, (2) the partial dissociation of these factors upon rearrangement of the gross structure of the spliceosome and the accompanying disruption and formation of protein-protein, RNA-RNA, and protein-RNA binding, (3) the completion of the two transesterifi cation steps, and (4) the release of the mature mRNA generated (for detailed review see [ 25 ]). …”