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. Author manuscript; available in PMC: 2013 Jul 17.
Published in final edited form as: Biochemistry. 2012 Jun 29;51(28):5541–5556. doi: 10.1021/bi3007065

Figure 2. Spliceosome assembly and splicing reaction.

Figure 2

From top, clockwise: U1 snRNP associates with the 5' splice site to make complex E. U2 snRNP is recruited and brings the branch site near the 5' splice site, forming complex A. The U4/U6.U5 tri-snRNP is recruited to form a pre-catalytic complex B. The arrival of the nineteen complex (NTC) and the release of U1 and U4 snRNAs mark the conversion to complex B*, an active spliceosome. Complex C forms after the first transesterification reaction and carries out the second transesterification reaction. The mature message is released and the post-splicing complex is recycled.