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In-Depth Information
Another damage amplification reaction has been observed with a dinucleo-
tide model which allowed to generate a Thy-5-yl radical specifically. In the pres-
ence of O
2
, it causes the formation of the 2-dRL lesion at the adjacent nucleotide
unit (Chap. 10.3). Based on this,
•
OH-addition to
C
(6) of T and C could give rise
to this tandem lesion also in DNA (as yet not detected).
It is as not known to what extent the observed formation of 2-dRL in DNA is due
to such a tandem lesion (see a lso Sect. 12.4.4 ; note t hat H1
is hidden in t he minor
groove (Sect. 12.2) and not very likely to be attacked by freely-diffusing reactive
radicals such as
•
OH).
′
12 . 6
DNA-DNA Cross-Links and DNA-Protein Cross-Links
12 . 6.1
DNA/DNA Cross-Links
Several types of DNA
DNA cross-links may be envisaged. Cross-linking of two
DNA molecules that lead to an increase in the molecular weight is original defi-
nition of a DNA/DNA cross-link. As cellular systems are concerned, this is a
rather unlikely event. In a mammalian cell, for example, a cross-link between
two chromosomes would have to occur. Thus, this type of DNA damage is re-
stricted to artificial systems such as irradiation of DNA in the solid state (Lücke-
Huhle et al. 1970). Interestingly, absence or presence of O
2
has practically no ef-
fect on their yields under such conditions, while SSB and DSB yields are doubled
in its presence. Data obtained with artificial polymers in aqueous solution sug-
gest that recombination of two DNA radicals situated at the same DNA should
be a much more likely process than a recombination of two radicals at different
DNA macromolecules (Chap. 9.6). This would form a kind of loop and would not
be connected with an increase in molecular weight (for a tandem lesion connect-
ing two opposite bases see Sect. 12.5.1; for interstrand cross-links by enediyne
−
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