The crystal structure of an RNA oligomer incorporating tandem adenosine-inosine mismatches |
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Authors: | RJ Carter KJ Baeyens J SantaLucia DH Turner SR Holbrook |
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Affiliation: | Structural Biology Division, Lawrence Berkeley Laboratory, Berkeley, CA 94720, USA. |
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Abstract: | The X-ray crystallographic structure of the RNA duplex r(CGCAIGCG)]2 has been refined to 2.5 A. It shows a symmetric internal loop of two non-Watson-Crick base pairs which form in the middle of the duplex. The tandem A-I/I-A pairs are related by a crystallographic two-fold axis. Both A(anti)-I(anti) mismatches are in a head-to-head conformation forming hydrogen bonds using the Watson-Crick positions. The octamer duplexes stack above one another in the cell forming a pseudo-infinite helix throughout the crystal. A hydrated calcium ion bridges between the 3'-terminal of one molecule and the backbone of another. The tandem A-I mismatches are incorporated with only minor distortion to the backbone. This is in contrast to the large helical perturbations often produced by sheared G-A pairs in RNA oligonucleotides. |
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