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PDBsum entry 1s47
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References listed in PDB file
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Key reference
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Title
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A thymine tetrad in d(tggggt) quadruplexes stabilized with tl+/na+ ions.
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Authors
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C.Cáceres,
G.Wright,
C.Gouyette,
G.Parkinson,
J.A.Subirana.
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Ref.
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Nucleic Acids Res, 2004,
32,
1097-1102.
[DOI no: ]
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PubMed id
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Abstract
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We report two new structures of the quadruplex d(TGGGGT)4 obtained by single
crystal X-ray diffraction. In one of them a thymine tetrad is found. Thus the
yeast telomere sequences d(TG1-3) might be able to form continuous quadruplex
structures, involving both guanine and thymine tetrads. Our study also shows
substantial differences in the arrangement of thymines when compared with
previous studies. We find five different types of organization: (i) groove
binding with hydrogen bonds to guanines from a neighbour quadruplex; (ii)
partially ordered groove binding, without any hydrogen bond; (iii) stacked
thymine triads, formed at the 3'ends of the quadruplexes; (iv) a thymine tetrad
between two guanine tetrads. Thymines are stabilized in pairs by single hydrogen
bonds. A central sodium ion interacts with two thymines and contributes to the
tetrad structure. (v) Completely disordered thymines which do not show any clear
location in the crystal. The tetrads are stabilized by either Na+ or Tl+ ions.
We show that by using MAD methods, Tl+ can be unambiguously located and
distinguished from Na+. We can thus determine the preference for either ion in
each ionic site of the structure under the conditions used by us.
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Headers
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