The purpose of this work was to gain insight into the formation of interstr
and cross-links in DNA triple helices resulting from the association betwee
n double-stranded DNAs and the complementary oligonucleotides containing a
single transplatin monofunctional adduct either trans-[Pt(NH3)(2)(dG)Cl](+)
or trans-[Pt(NH3)(2)(dC)Cl](+). Depending upon its location along the olig
onucleotide, a platinated guanine residue increases or decreases the therma
l stability of the platinated triplexes, as shown on model systems in which
the transplatin monofunctional adduct was replaced by a diethylenetriamine
platinum(II) adduct. The interstrand cross-linking reaction has been studie
d in triplexes containing a single transplatin monofunctional adduct as a f
unction of several parameters. The rate of closure of the monofunctional ad
duct into an interstrand cross-link depends upon the nature of the adduct b
ut not strongly on its location along the Hoogsteen strand. The closure of
trans-[Pt(NH3)(2)(dC)Cl](+) is faster than that of trans-[Pt(NH3)(2)(dG)Cl]
(+). Whereas the closure of trans-[Pt(NH3)(2)(dC)Cl](+) is hardly affected
by the presence of a high concentration of NaCl in the medium, the closure
of trans-[Pt(NH3)(2)(dG)Cl](+) is largely slowed down. These results are di
scussed in the context of the potential use of the platinated oligonucleoti
des to modulate gene expression.