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[[Image:260d.gif|left|200px]]


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==CRYSTAL STRUCTURE OF THE SELF-COMPLEMENTARY 5'-PURINE START DECAMER D(GCACGCGTGC) IN THE A-DNA CONFORMATION-PART II==
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<StructureSection load='260d' size='340' side='right'caption='[[260d]], [[Resolution|resolution]] 1.90&Aring;' scene=''>
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== Structural highlights ==
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<table><tr><td colspan='2'>[[260d]] is a 1 chain structure. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=260D OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=260D FirstGlance]. <br>
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</td></tr><tr id='method'><td class="sblockLbl"><b>[[Empirical_models|Method:]]</b></td><td class="sblockDat" id="methodDat">X-ray diffraction, [[Resolution|Resolution]] 1.9&#8491;</td></tr>
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<tr id='resources'><td class="sblockLbl"><b>Resources:</b></td><td class="sblockDat"><span class='plainlinks'>[https://proteopedia.org/fgij/fg.htm?mol=260d FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=260d OCA], [https://pdbe.org/260d PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=260d RCSB], [https://www.ebi.ac.uk/pdbsum/260d PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=260d ProSAT]</span></td></tr>
{{STRUCTURE_260d|  PDB=260d  |  SCENE= }}
</table>
 
__TOC__
'''CRYSTAL STRUCTURE OF THE SELF-COMPLEMENTARY 5'-PURINE START DECAMER D(GCACGCGTGC) IN THE A-DNA CONFORMATION-PART II'''
</StructureSection>
 
[[Category: Large Structures]]
 
[[Category: Ban C]]
==Overview==
[[Category: Sundaralingam M]]
The crystal structure of the alternating 5'-purine start decamer d(GCGCGCGCGC) was found to be in the left-handed Z-DNA conformation. Inasmuch as the A.T base pair is known to resist Z-DNA formation, we substituted A.T base pairs in the dyad-related positions of the decamer duplex. The alternating self-complementary decamer d(GCACGCGTGC) crystallizes in a different hexagonal space group, P6(1)22, with very different unit cell dimensions a = b = 38.97 and c = 77.34 A compared with the all-G.C alternating decamer. The A.T-containing decamer has one strand in the asymmetric unit, and because it is isomorphous to some other A-DNA decamers it was considered also to be right-handed. The structure was refined, starting with the atomic coordinates of the A-DNA decamer d(GCGGGCCCGC), by use of 2491 unique reflections out to 1.9-A resolution. The refinement converged to an R value of 18.6% for a total of 202 nucleotide atoms and 32 water molecules. This research further demonstrates that A.T base pairs not only resist the formation of Z-DNA but can also assist the formation of A-DNA by switching the helix handedness when the oligomer starts with a 5'-purine; also, the length of the inner Z-DNA stretch (d(CG)n) is reduced from an octamer to a tetramer. It may be noted that these oligonucleotide properties are in crystals and not necessarily in solutions.
 
==About this Structure==
Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=260D OCA].  
 
==Reference==
Crystal structure of the self-complementary 5'-purine start decamer d(GCACGCGTGC) in the A-DNA conformation. II., Ban C, Sundaralingam M, Biophys J. 1996 Sep;71(3):1222-7. PMID:[http://www.ncbi.nlm.nih.gov/pubmed/8873996 8873996]
[[Category: Ban, C.]]
[[Category: Sundaralingam, M.]]
[[Category: A-dna]]
[[Category: Double helix]]
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