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Mol. Cell. Biol., 02 1997, 760-769, Vol 17, No. 2
D Mu, M Tursun, DR Duckett, JT Drummond, P Modrich and A Sancar
Nucleotide excision repair and the long-patch mismatch repair systems
correct abnormal DNA structures arising from DNA damage and replication
errors, respectively. DNA synthesis past a damaged base (translesion
replication) often causes misincorporation at the lesion site. In addition,
mismatches are hot spots for DNA damage because of increased susceptibility
of unpaired bases to chemical modification. We call such a DNA lesion, that
is, a base damage superimposed on a mismatch, a compound lesion. To learn
about the processing of compound lesions by human cells, synthetic compound
lesions containing UV photoproducts or cisplatin 1,2-d(GpG) intrastrand
cross-link and mismatch were tested for binding to the human mismatch
recognition complex hMutS alpha and for excision by the human excision
nuclease. No functional overlap between excision repair and mismatch repair
was observed. The presence of a thymine dimer or a cisplatin diadduct in
the context of a G-T mismatch reduced the affinity of hMutS alpha for the
mismatch. In contrast, the damaged bases in these compound lesions were
excised three- to fourfold faster than simple lesions by the human excision
nuclease, regardless of the presence of hMutS alpha in the reaction. These
results provide a new perspective on how excision repair, a cellular
defense system for maintaining genomic integrity, can fix mutations under
certain circumstances.
Copyright © 1997, American Society for Microbiology
Recognition and repair of compound DNA lesions (base damage and mismatch) by human mismatch repair and excision repair systems
Department of Biochemistry and Biophysics, University of North Carolina School of Medicine, Chapel Hill 27599-7260, USA.
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