NUCLEOTICE EXCISION REPAIR, NER
Applies to bulky adducts and distortions of the double helix: e.g.
- Cyclobutane pyrimidine dimers induced by UV light.
Differs from base excision repair.
The disease XP is characterised by molucular defects in NER.
Half-time for repair: a few hours
Figure Many proteins are involved in NER. The damage is recognised, and a complex of proteins is bound to the DNA. Two endonuclease activities operate, on either side of the lesion, about 28 bases apart, so the damage is excised within an oligonucleotide. Repair synthesis, to fill this gap, is much more substantial than in the case of BER, and it can be detected – using radioactively labelled DNA precursor – as the incorporation of label into non-S-phase cells. This is known as unscheduled DNA synthesis (UDS).