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5-methyl-5-hydroxyhydantoin (from T) and 1-carbamoyl-2-oxo-4,5-dihydroxy-
imidazolidine (from C). Moreover, the tandem lesion consisting of an 8-oxo-G
next to a Fo (from T) lesion was also identified (for mechanistic aspects and
importance of tandem lesion, see Chaps 10.6 and 12.5). Besides the 8-oxo-G/Fo
lesion (in the presence of O
2
), the tandem lesion, linking the methyl group of T to
C
(8) of a neighboring G, is observed with d(CpGpTpA) in the absence of O
2
, and
it has been noted that the tandem lesions were of greater importance than any of
the simple lesions (Box et al. 1996; Budzinski et al. 1997). The scission products
dCp, d(CpGp), dpA, d(pTpA) and d(GpTpA) were also detected.
In an extension of this study, some further tandem lesions were detected in
d(CpGpTpA) and d(CpApTpG) (Box et al. 1998). The cross-linked tandem base
lesions shown below are only formed in the absence of O
2
.
It is reasonable to assume that the H
•
- and
•
OH-adducts at
C
(5) of C bind to
C
(8)
of the neighboring G, and the resulting adduct radical is oxidized in subsequent
free-radical termination reactions. While the H
•
-adduct product (on the right)
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