225d
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(New page: 200px<br /><applet load="225d" size="350" color="white" frame="true" align="right" spinBox="true" caption="225d" /> '''A TETRAMERIC DNA STRUCTURE WITH PROTONATED C...)
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Revision as of 15:47, 29 January 2008
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A TETRAMERIC DNA STRUCTURE WITH PROTONATED CYTOSINE:CYTOSINE BASE PAIRS
Overview
Oligomers containing tracts of cytidine form hemiprotonated base pairs at, acid pH and have been considered to be double-stranded. We have solved the, structure of the DNA oligomer 5'-d(TCCCCC) at acid pH and find that it is, a four-stranded complex in which two base-paired parallel-stranded, duplexes are intimately associated, with their base pairs fully, intercalated. The relative orientation of the duplexes is antiparallel, so, that each base pair is face-to-face with its neighbours. The NMR spectrum, displays only six spin systems, showing that the structure is highly, symmetrical on the NMR timescale; the four strands are equivalent. A model, derived by energy minimization and constrained molecular dynamics shows, excellent compatibility with the observed nuclear Overhauser effects, (NOEs) particularly for the very unusual inter-residue sugar-sugar NOEs, H1'-H1', H1'-H2" and H1'-H4'. These NOEs are probably diagnostic for such, tetrameric structures.
About this Structure
225D is a Protein complex structure of sequences from [1]. Full crystallographic information is available from OCA.
Reference
A tetrameric DNA structure with protonated cytosine.cytosine base pairs., Gehring K, Leroy JL, Gueron M, Nature. 1993 Jun 10;363(6429):561-5. PMID:8389423
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