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Lodish H, Berk A, Zipursky SL, et al. Molecular Cell Biology. 4th edition. New York: W. H. Freeman; 2000.

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Molecular Cell Biology. 4th edition.

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Figure 11-19. The spliceosomal splicing cycle.

Figure 11-19The spliceosomal splicing cycle

The splicing snRNPs (U1, U2, U4, U5, and U6) associate with the pre-mRNA and with each other in an ordered sequence to form the spliceosome. This large ribonucleoprotein complex then catalyzes the two transesterification reactions that result in splicing of the exons (light and dark red) and excision of the intron (blue) as a lariat structure (see Figure 11-16). Although ATP hydrolysis is not required for the transesterification reactions, it is thought to provide the energy necessary for rearrangements of the spliceosome structure that occur during the cycle. Note that the snRNP proteins in the spliceosome are distinct from the hnRNP proteins discussed earlier. In higher eukaryotes, the association of U2 snRNP with pre-mRNA is assisted by an hnRNP protein called U2AF, which binds to the pyrimidine-rich region near the 3′ splice site. U2AF also probably interacts with other proteins required for splicing through a domain containing repeats of the dipeptide serine-arginine (the SR motif). The branch-point A in pre-mRNA is indicated in boldface. [See S. W. Ruby and J. Abelson, 1991, Trends Genet. 7:79; adapted from M. J. Moore et al., 1993, in R. Gesteland and J. Atkins, eds., The RNA World, Cold Spring Harbor Press, pp. 303-357.]

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View Movie: mRNA Splicing

From: Section 11.2, Processing of Eukaryotic mRNA

Copyright © 2000, W. H. Freeman and Company.


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