Nucleic Acids Research, Vol 27, Issue 13 2699-2707, Copyright © 1999 by Oxford University Press
A Debin, C Laboulais, M Ouali, C Malvy, M Le Bret and F Svinarchuk
In this work we selected double-stranded DNA sequences capable of forming
stable triplexes at 20 or 50 degrees C with corresponding 13mer purine
oligonucleotides. This selection was obtained by a double aptamer approach
where both the starting sequences of the oligonucleotides and the target
DNA duplex were random. The results of selection were confirmed by a cold
exchange method and the influence of the position of a 'mismatch' on the
stability of the triplex was documented in several cases. The selected
sequences obey two rules: (i) they have a high G content; (ii) for a given
G content the stability of the resulting triplex is higher if the G
residues lie in stretches. The computer simulation of the Mg2+, Na+and
Cl-environment around three triplexes by a density scaled Monte Carlo
method provides an interpretation of the experimental observations. The
Mg2+cations are statistically close to the G N7 and relatively far from the
A N7. The presence of an A repels the Mg2+from adjacent G residues.
Therefore, the triplexes are stabilized when the Mg2+can form a continuous
spine on G N7.
ARTICLES
Stability of G,A triple helices
CNRS UMR 8532, Institut Gustave-Roussy, 94805 Villejuif, France.
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