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region showed only globules on the glass surface (Figure 3b);
after the addition of the RR enantiomer the number of
globules on the glass surface decreased, and many DNA
molecules containing both folded and unfolded parts
appeared (Figure 3c). The appearance of these structures
on the glass surface upon the addition of the RR compound is
also attributed to the phenomenon of unfolding. This
phenomenon appears to be a direct result of the antagonistic
effect that the SS and RR enantiomers have on one another in
DNA compaction. Since DNA compaction is a reversible
process, the exchange of dications at suitable sites in the
exposed regions of the DNA chains in a compact globule
results in the partial populating of DNA by the RR dication,
which initiates unfolding. The importance of this finding is
that a noncomplementary enantiomer can be used not only to
prevent the formation of the DNA compact state by the
complementary enantiomer, but also to promote the reverse
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In summary, a dramatic difference and conflict was
observed between two synthetic enantiomeric dications in
their effect on the compaction of giant T4 DNA. As no
difference was found in the DNA-binding activity of the two
enantiomers, the results obtained regarding chiral discrim-
ination in DNA compaction indicate that the selectivity for an
enantiomer with complementary chirality has its origin in the
DNA-folding process itself. It was also demonstrated that an
achiral dication can remove the structural chirality restric-
tions during DNA compaction by enantiomers. In nature,
where DNA folding and unfolding are fundamental processes,
chiral discrimination in the DNA compaction may be one of
the selection mechanisms toward biochemical homochirality.
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Supporting Information.
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Received: January 19, 2004 [Z53774]
Keywords: chiral discrimination · chirality · DNA compaction ·
.
DNA recognition · fluorescence microscopy
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