Formation of the Spliceosomal P complex and exon ligation

Stable Identifier
Reaction [uncertain]
Homo sapiens
Second catalytic step of mRNA splicing
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Two magnesium ions coordinated by 4 phosphate groups of the U6 snRNA in the Spliceosomal C* complex (Bertram et al. 2017, Zhang et al. 2017) catalyze the transesterification reaction between the 3' nucleotide residue of the upstream exon and the 5' nucleotide residue of the downstream exon. The 3' hydroxyl group of the upstream exon nucleophilically attacks the 5' phosphate group of the downstream exon and the magnesium ions stabilize the pentacovalent transition state. Upon completion of exon ligation, the Spliceosomal P complex (post-catalytic complex) is formed. CACTIN, SDE2, NKAP, and PKRIP1 originally present in the Spliceosomal C* complex stabilize the branch helix (Fica et al. 2019, Zhang et al. 2019). FAM32A, not found in yeast, bridges the upstream exon and the 3' splice site of the intron in the Spliceosomal P complex (Fica et al. 2019). An Exon Junction Complex (EJC) is bound to the upstream exon 20-24 nucleotides upstream of the splice site (Zhang and Krainer 2007, Zhang et al. 2019). SRRM2 and CWC22 are also bound to the upstream exon (Zhang et al. 2019). ALYREF, which was initially recruited to the cap binding complex of the early spliceosome, now becomes associated with EJCs and nearby regions on the spliced mRNA (Zhou et al. 2000, Chi et al. 2013). Auxiliary factors, the ASAP complex or the PSAP complex also bind the EJC (Tange et al. 2005). DHX8 (homolog of yeast Prp22) which will dissociate the spliced mRNP from the Intron Lariat Spliceosome is bound to PRPF8 (homolog of yeast Prp8) (Zhang et al. 2019). The components of the Spliceosomal P complex have been ascertained using proteomic and structural methods (Kataoka and Dreyfuss 2004, Ilagan et al. 2013, Fica et al. 2019).
Literature References
PubMed ID Title Journal Year
16314458 Biochemical analysis of the EJC reveals two new factors and a stable tetrameric protein core

Tange, TØ, Moore, MJ, Jurica, MS, Shibuya, T

RNA 2005
11014198 The protein Aly links pre-messenger-RNA splicing to nuclear export in metazoans

Reed, R, Luo, MJ, Katahira, J, Hurt, E, Straesser, K, Zhou, Z

Nature 2000
23222130 Aly and THO are required for assembly of the human TREX complex and association of TREX components with the spliced mRNA

Chang, X, Shi, M, Wu, G, Chi, B, Wang, L, Tan, M, Wang, Q, Cheng, H

Nucleic Acids Res. 2013
28076346 Cryo-EM structure of a human spliceosome activated for step 2 of splicing

Bertram, K, Will, CL, Lührmann, R, Dybkov, O, Agafonov, DE, Stark, H, Urlaub, H, Kastner, B, Hartmuth, K, Liu, WT

Nature 2017
28502770 An Atomic Structure of the Human Spliceosome

Yan, C, Shi, Y, Zhang, X, Finci, LI, Lei, J, Hang, J

Cell 2017
23345524 Rearrangements within human spliceosomes captured after exon ligation

Ilagan, JO, Chalkley, RJ, Jurica, MS, Burlingame, AL

RNA 2013
14625303 A simple whole cell lysate system for in vitro splicing reveals a stepwise assembly of the exon-exon junction complex

Kataoka, N, Dreyfuss, G

J Biol Chem 2004
30728453 Structures of the human spliceosomes before and after release of the ligated exon

Shi, Y, Liu, D, Yan, C, Zhang, W, Zhang, X, Lei, J, Zhan, X

Cell Res 2019
30705154 A human postcatalytic spliceosome structure reveals essential roles of metazoan factors for exon ligation

Wilkinson, ME, Fica, SM, Nagai, K, Newman, AJ, Oubridge, C

Science 2019
17606899 Splicing remodels messenger ribonucleoprotein architecture via eIF4A3-dependent and -independent recruitment of exon junction complex components

Krainer, AR, Zhang, Z

Proc Natl Acad Sci U S A 2007
Catalyst Activity

second spliceosomal transesterification activity of Spliceosomal C* complex [nucleoplasm]

Orthologous Events
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