Two pathways for nucleotide-excision repair

The nucleotide-excision repair pathway is activated when bulky adducts or multiple damaged bases are recognized in nontranscribed (GG-NER) or transcribed (TC-NER) regions of the genome. These two pathways are initiated by different events and distinct complexes, as shown in the first step. Both complexes serve to attract the same TFIIH complex (Step 2). The recognition complexes are removed in Step 3 (not shown). In steps 4-6, a multiprotein complex excises several bases and resynthesizes them using the opposite strand as a template. See text for details.