Research ArticleStructural Biology

Structural basis of pre-mRNA splicing

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Science  20 Aug 2015:
aac8159
DOI: 10.1126/science.aac8159

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Abstract

Splicing of pre-mRNA is performed by the spliceosome. In the cryo-EM structure of the yeast spliceosome, U5 snRNP acts as a central scaffold onto which U6 and U2 snRNAs are intertwined to form a catalytic center next to Loop I of U5 snRNA. Magnesium ions are coordinated by conserved nucleotides in U6 snRNA. The intron lariat is held in place through base pairing interactions with both U2 and U6 snRNAs, leaving the variable-length middle portion on the solvent-accessible surface of the catalytic center. The protein components of the spliceosome anchor both 5′- and 3′-ends of the U2 and U6 snRNAs away from the active site, direct the RNA sequences, and allow sufficient flexibility between the ends and the catalytic center. Thus, the spliceosome is in essence a protein-directed ribozyme, with the protein components essential for the delivery of critical RNA molecules into close proximity of one another at the right time for the splicing reaction.

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