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. Author manuscript; available in PMC: 2012 Sep 1.
Published in final edited form as: J Invest Dermatol. 2012 Jan 5;132(3 0 2):785–796. doi: 10.1038/jid.2011.426

Figure 3.

Figure 3

Nucleotide excision repair (NER) pathway. Transcription coupled repair (TCR) removes damage from actively transcribing genes while global genome repair (GGR) removes damage from the remainder of the genome. In GGR damage such as ultraviolet induced cyclobutane pyrimidine dimers (CPD) or 6-4 photoproducts (6-4 PP) are recognized by proteins including the XPE (DDB2) and XPC gene products. In TCR, the lesion appears to block the progress of RNA polymerase II in a process involving the CSA and CSB gene products. Following initial damage recognition the pathways converge. The XPB (ERCC3) and XPD (ERCC2) helicases unwind the region surrounding the lesion along with the XPA and XPG (ERCC5) gene products, and replication protein A (RPA). The XPF and XPG (ERCC5) endonucleases perform incisions to remove the lesion in a fragment of about 30 nucleotides. The resulting gap is filled in by de novo DNA synthesis. This system is coordinated so that if one part of the pathway is mutated the entire pathway fails to function normally. Mutations in the genes in rectangles have been associated with clinical disease. This diagram is modified from (Van Steeg and Kraemer 1999; Kraemer et al. 2007).