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Nat Struct Biol. 1995 Jan;2(1):56-62.

Structure of an RNA double helix including uracil-uracil base pairs in an internal loop.

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Structural Biology Division, Lawrence Berkeley Laboratory, University of California, Berkeley 94720.


The crystal structure of the RNA dodecamer 5'-GGACUUUGGUCC-3' has been determined from X-ray diffraction data to 2.6 A resolution. This oligomer forms an asymmetric double helix in the crystal. Four consecutive non-Watson-Crick base-pairs are formed in the middle of the duplex including the first intrahelical U-U (or T-T) pairs observed in an oligonucleotide crystal structure. Two different conformations of U-U pairs are observed in the context of the surrounding sequence. One of these pairs is highly twisted, allowing a bound water to bridge across strands in the major groove. The crystal packing illustrates a new form of RNA helix-helix interaction.

[Indexed for MEDLINE]

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