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==A SINGLE 2'-HYDROXYL GROUP CONVERTS B-DNA TO A-DNA: CRYSTAL STRUCTURE OF THE DNA-RNA CHIMERIC DECAMER DUPLEX D(CCGGC)R(G)D(CCGG) WITH A NOVEL INTERMOLECULAR G.C BASE-PAIRED QUADRUPLET==
<StructureSection load='161d' size='340' side='right' caption='[[161d]], [[Resolution|resolution]] 1.90&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[161d]] is a 2 chain structure. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=161D OCA]. For a <b>guided tour on the structure components</b> use [http://oca.weizmann.ac.il/oca-docs/fgij/fg.htm?mol=161D FirstGlance]. <br>
</td></tr><tr id='resources'><td class="sblockLbl"><b>Resources:</b></td><td class="sblockDat"><span class='plainlinks'>[http://oca.weizmann.ac.il/oca-docs/fgij/fg.htm?mol=161d FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=161d OCA], [http://pdbe.org/161d PDBe], [http://www.rcsb.org/pdb/explore.do?structureId=161d RCSB], [http://www.ebi.ac.uk/pdbsum/161d PDBsum]</span></td></tr>
</table>
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== Publication Abstract from PubMed ==
We have found that the introduction of a single 2'-hydroxyl group on the sugar-phosphate backbone of the B-DNA decamer d(CCGGCGCCGG) transforms it to A-DNA. Thus, for the first time the X-ray structures of the same sequence have been observed in both the A and B-DNA conformations, permitting a comparison. Crystals of the DNA-RNA chimeric decamer d(CCGGC)r(G)d(CCGG) belong to the orthorhombic space group P2(1)2(1)2(1) with unit cell dimensions a = 25.63 A, b = 45.24 A and c = 47.99 A, and one decamer duplex in the asymmetric unit. The structure was solved by a rigid body search using the coordinates of the isomorphous structure d(CCCGGCCGGG) and refined to an R value of 0.136 using 2753 unique reflections at 1.9 A resolution. The final model contains 406 nucleotide atoms and 61 water molecules. The chimeric duplex exhibits typical A-DNA geometry, with all the sugars in the C(3')-endo puckering and the base-pairs inclined and displaced from the helix axis. The 2'-hydroxyl groups on rG6 and rG16 protrude into the minor groove surface and form different types of hydrogen bonds; that on strand 1 forms an intermolecular hydrogen bond with the furanose ring O(4') of a symmetry-related C1 residue, while that on strand 2 is involved in two water bridges. Crystal packing forces the G4-G17 base-pair in the top half of the duplex to slide significantly into the minor groove compared to the corresponding G7-G14 base-pair in the bottom half, resulting in these base-pairs exhibiting different base stacking and intermolecular interactions. The base G4 of the G4-G17 base-pair forms an unorthodox base "triple", G4*(G10-C11), hydrogen-bonding through its minor groove sites N(2) and N(3) to the minor groove atoms N(2) and O(2) of both bases of the G10-C11 base-pair of a symmetry-related molecule. The base G10 of this triple in turn forms a second similar unorthodox base triple, G10*(G3*C18), with the adjacent base-pair G3-C18 of the duplex, thus G10 is involved in a double triple. On the other hand, in the bottom half of the duplex, the C7-G14 base-pair is involved only in a single similar unorthodox base triple with G20, (C7-G14)*G20, while the adjacent base-pair rG6-C15 is involved in a novel quadruple with C1-G20, (rG6-C15) *(C1-G20), where the latter base-pairs are hydrogen-bonded to each other via the minor groove sites G(N(2))...C(O(2)).(ABSTRACT TRUNCATED AT 400 WORDS)

A single 2'-hydroxyl group converts B-DNA to A-DNA. Crystal structure of the DNA-RNA chimeric decamer duplex d(CCGGC)r(G)d(CCGG) with a novel intermolecular G-C base-paired quadruplet.,Ban C, Ramakrishnan B, Sundaralingam M J Mol Biol. 1994 Feb 11;236(1):275-85. PMID:7508984<ref>PMID:7508984</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
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<div class="pdbe-citations 161d" style="background-color:#fffaf0;"></div>
== References ==
<references/>
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</StructureSection>
[[Category: Ban, C]]
[[Category: Ramakrishnan, B]]
[[Category: Sundaralingam, M]]
[[Category: A-dna/rna]]
[[Category: Dna-rna hybrid]]
[[Category: Double helix]]