Nucleic Acids Research, Vol 27, Issue 8 1802-1809, Copyright © 1999 by Oxford University Press
J Bijapur, MD Keppler, S Bergqvist, T Brown and KR Fox
We have used quantitative DNase I footprinting and UV-melting studies to
examine the formation of DNA triplexes in which the third strand thymines
have been replaced by 5-propargylamino-dU (UP). The intra- molecular
triplex A6-L-T6-L-(UP)5T (L = two octanediol residues) shows a single
UV-melting transition which is >20 degrees higher than that of the
parent triplex A6-L-T6-L-T6at pH 5.5. Although a single transition is
observed at all pHs, the melting temperature (Tm) of the modified
oligonucleotide decreases at higher pHs, consistent with the requirement
for protonation of the amino group. A similar intramolecular triplex with a
longer overhanging duplex shows two melting transitions, the lower of which
is stabilised by substitution of T by UP, in a pH dependent fashion.
Triplex stability increases by approximately 12 K for each T to UP
substitution. Quantitative footprinting studies have examined the
interaction of three UP- containing 9mer oligonucleotides with the
different portions of the 17mer sequence 5'-AGGAAGAGAAAAAAGAA. At pH 5.0,
the UP-containing oligo- nucleotides footprint to much lower concentrations
than their T- containing counterparts. In particular (UP)6CUPT binds
approximately 1000-fold more tightly than the unmodified oligonucleotide
T6CTT. Oligonucleotides containing fewer UP residues are stabilised to a
lesser extent. The affinity of these modified third strands decreases at
higher pHs. These results demonstrate that the stability of DNA triplexes
can be dramatically increased by using positively charged analogues of
thymine.
ARTICLES
5-(1-propargylamino)-2'-deoxyuridine (UP): a novel thymidine analogue for generating DNA triplexes with increased stability
Department of Chemistry, University of Southampton, Highfield, Southampton, SO17 1BJ, UK.
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