Nucleic Acids Research, Vol 27, Issue 24 4759-4767, Copyright © 1999 by Oxford University Press
S Leporc, O Mauffret, G Tevanian, E Lescot, M Monnot and S Fermandjian
In a previous NMR study we detected the presence of particular motions and
hydration properties within the DNA fragment
d(CTACTGCTTTAG).d(CTAAAGCAGTAG). Now, we report on an NMR and molecular
modelling analysis of this sequence focusing our attention on the
biologically important TpA steps. NOe and coupling constant restraints were
introduced in three different modelling protocols: X-PLOR and JUMNA used
with Flex and AMBER94 as force-fields. Despite their differences the
protocols produce similar mean B-DNA structures (r.m.s.d. <1 A). The new
information confirms our previous experimental results on the narrowing of
the minor groove along the T8T9T10/A17A16A15 run and the sudden widening at
the T10pA11 step ending this run. It is further shown that this step
displays a large positive roll with its T10:A15 and A11:T14 base-pairs
likely stabilised by amino-amino and amino-carbonyl interactions in the
major groove. A relationship between roll values and amino-amino and
amino-carbonyl distances strongly suggests that electrostatics or
bifurcated hydrogen- bonds could be responsible for induction of positive
rolls in TpA steps. Such edge-to-edge interactions could explain the slower
motions shown by the adenine A15. The influence of these interactions on
the stabilisation of particular DNA conformers is discussed using our data
and those provided by the recent literature.
ARTICLES
An NMR and molecular modelling analysis of d(CTACTGCTTTAG). d(CTAAAGCAGTAG) reveals that the particular behaviour of TpA steps is related to edge-to-edge contacts of their base-pairs in the major groove
Departement de Biologie Structurale, UMR 8532 CNRS, Institut Gustave Roussy, 39-53 rue Camille Desmoulins, 94805 Villejuif, France.
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