Spliceosomal Machinery


‘Spliceosomal Machinery’ describes how various small nuclear ribonucleic acids (snRNAs) and over 100 proteins interact to perform the precise removal of introns from eukaryotic pre‐messenger RNAs. The conserved major U2‐spliceosome machinery is the main focus of this article and other minor spliceosomes are also described, as well as an introduction to factors involved in regulating splicing.

Keywords: spliceosome; snRNA; snRNP; RNA splicing; intron

Figure 1.

(a) Intron removal involves two trans‐esterification reactions. First, the branch point adenosine within the intron cleaves the phosphodiester bond at the 5′‐end of the intron, and a new phosphodiester bond is formed to produce a lariat intermediate. Secondly, the other intermediate product, exon 1, attacks the phosphodiester bond at the 3′SS to produce the spliced mRNA. The intron is excised as a lariat byproduct that is processed further. (b) Three different types of intron sequences are recognized by different groups of snRNPs. The conserved intronic sequences are shown above each type of intron, Yn represents a polypyrimidine tract and R means a purine. The different 5′SS and branchpoint sequences determine which spliceosome they will be spliced by.

Figure 2.

Simplified schematic showing the conserved snRNP rearrangements during spliceosome assembly and activation.

Figure 3.

Schematic of the early stages of spliceosome assembly. The black shapes represent DExH/D proteins that promote rearrangements of RNA–protein interactions at the branchpoint adenosine.

Figure 4.

A schematic illustrating the involvement of SFs in intron commitment and/or exon definition on a pre‐mRNA. CPC, cap‐binding complex; ESE (striped block), exon splicing enhancer.

Figure 5.

Schematic showing the cycle of assembly and disassembly of the U2‐spliceosomal machinery upon pre‐mRNA. The black shapes represent the DExD/H box proteins, their positions indicating their functional requirement at specific spliceosomal stages.



Ajuh P, Kuster B, Panov K et al. (2000) Functional analysis of the human CDC5L complex and identification of its components by mass spectrometry. EMBO Journal 19(23): 6569–6581.

Behzadnia N, Golas MM, Hartmuth K et al. (2007) Composition and three‐dimensional EM structure of double affinity‐purified, human prespliceosomal A complexes. EMBO Journal 26(6): 1737–1748.

Chen CH, Yu WC, Tsao TY et al. (2002) Functional and physical interactions between components of the Prp19p‐associated complex. Nucleic Acids Research 30(4): 1029–1037.

Deckert J, Hartmuth K, Boehringer D et al. (2006) Protein composition and electron microscopy structure of affinity‐purified human spliceosomal B complexes isolated under physiological conditions. Molecular and Cellular Biology 26(14): 5528–5543.

Gottschalk A, Neubauer G, Banroques J et al. (1999) Identification by mass spectrometry and functional analysis of novel proteins of the yeast [U4/U6.U5] tri‐snRNP. EMBO Journal 18(16): 4535–4548.

Grainger RJ and Beggs JD (2005) Prp8 protein: at the heart of the spliceosome. RNA 11(5): 533–557.

Hartmuth K, Urlaub H, Vornlocher HP et al. (2002) Protein composition of human prespliceosomes isolated by a tobramycin affinity‐selection method. Proceedings of the National Academy of Sciences of the USA 99(26): 16719–16724.

Jurica MS, Licklider LJ, Gygi SR, Grigorieff N and Moore MJ (2002) Purification and characterization of native spliceosomes suitable for three‐dimensional structural analysis. RNA 8(4): 426–439.

Jurica MS and Moore MJ (2003) Pre‐mRNA splicing: awash in a sea of proteins. Molecular Cell 12(1): 5–14.

Karni R, de Stanchina E, Lowe SW et al. (2007) The gene encoding the splicing factor SF2/ASF is a proto‐oncogene. Nature Structural & Molecular Biology 14(3): 185–193.

Kent OA, Ritchie DB and MacMillan AM (2005) Characterization of a U2AF‐independent commitment complex (E') in the mammalian spliceosome assembly pathway. Molecular and Cellular Biology 25(1): 233–240.

Makarov EM, Makarova OV, Urlaub H et al. (2002) Small nuclear ribonucleoprotein remodeling during catalytic activation of the spliceosome. Science 298(5601): 2205–2208.

Makarova OV, Makarov EM, Urlaub H et al. (2004) A subset of human 35S U5 proteins, including Prp19, function prior to catalytic step 1 of splicing. EMBO Journal 23(12): 2381–2391.

Ohi MD, Link AJ, Ren L et al. (2002) Proteomics analysis reveals stable multiprotein complexes in both fission and budding yeasts containing Myb‐related Cdc5p/Cef1p, novel pre‐mRNA splicing factors, and snRNAs. Molecular and Cellular Biology 22(7): 2011–2024.

Schellenberg MJ, Edwards RA, Ritchie DB et al. (2006) Crystal structure of a core spliceosomal protein interface. Proceedings of the National Academy of Sciences of the USA 103(5): 1266–1271.

Small EC, Leggett SR, Winans AA and Staley JP (2006) The EF‐G‐like GTPase Snu114p regulates spliceosome dynamics mediated by Brr2p, a DExD/H box ATPase. Molecular Cell 23(3): 389–399.

Stevens SW and Abelson J (1999) Purification of the yeast U4/U6.U5 small nuclear ribonucleoprotein particle and identification of its proteins. Proceedings of the National Academy of Sciences of the USA 96(13): 7226–7231.

Tycowski KT, Kolev NG, Conrad NK, Fok V and Steitz JA (2006) The ever‐growing world of small nuclear ribonucleoproteins. In: Gesteland RF, Cech TR and Atkins JF (eds) The RNA World, 3rd edn, pp. 327–368. New York: Cold Spring Harbor Laboratory Press.

Will CL and Luhrmann R (2006) The ever‐growing world of small nuclear ribonucleoproteins. In: Gesteland RF, Cech TR and Atkins JF (eds) The RNA World, 3rd edn, pp. 369–400. New York: Cold Spring Harbor Laboratory Press.

Further Reading

Chao H and Walsh CE (2006) RNA repair for haemophilia A. Expert Reviews in Molecular Medicine 8(1): 1–8.

Cordin O, Banroques J, Tanner NK and Linder P (2006) The DEAD‐box protein family of RNA helicases. Gene 367: 17–37.

Gesteland RF, Cech TR and Atkins JF (2006) The RNA World. New York: Cold Spring Harbor Laboratory Press.

Contact Editor close
Submit a note to the editor about this article by filling in the form below.

* Required Field

How to Cite close
Grainger, Richard J, and Beggs, Jean D(Dec 2007) Spliceosomal Machinery. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0000889.pub2]