DNA gap after NER is filled by
After excision of damaged oligonucleotide by UvrABC and helicase mediated release, single-stranded gap with intact complementary template remains requiring resynthesis for restoration of duplex. In bacteria DNA Polymerase I performs this fill-in using its 5'→3' polymerase activity, inserting nucleotides complementary to undamaged strand and using 3'-OH generated by upstream incision as primer. DNA ligase then seals final nick. Pol III generally not used for NER gap as patch short and associated with Pol I nick translation activity. In eukaryotes analogous role fulfilled by Pol delta or epsilon
Ref: Watson et al., Molecular Biology of the Gene, 7th ed., Chapter 10: Pol I Gap Filling After NER Excision
