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Nat Struct Mol Biol. 2004 Dec;11(12):1237-42. Epub 2004 Nov 14.

U2-U6 RNA folding reveals a group II intron-like domain and a four-helix junction.

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Department of Biochemistry, University of Wisconsin-Madison, 433 Babcock Drive, Madison, Wisconsin 53706, USA.

Erratum in

  • Nat Struct Mol Biol. 2005 Jan;12(1):99.


Intron removal in nuclear precursor mRNA is catalyzed through two transesterification reactions by a multi-megaDalton ribonucleoprotein machine called the spliceosome. A complex between U2 and U6 small nuclear RNAs is a core component of the spliceosome. Here we present an NMR structural analysis of a protein-free U2-U6 complex from Saccharomyces cerevisiae. The observed folding of the U2-U6 complex is a four-helix junction, in which the catalytically important AGC triad base-pairs only within U6 and not with U2. The base-pairing of the AGC triad extends the U6 intramolecular stem-loop (U6 ISL), and the NMR structure of this extended U6 ISL reveals structural similarities with domain 5 of group II self-splicing introns. The observed conformation of the four-helix junction could be relevant to the first, but not the second, step of splicing and may help to position the U6 ISL adjacent to the 5' splice site.

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