page_title: Nucleotide excision repair
section_title: Global genomic NER (GG-NER)
hierarchical_section_title: Nucleotide excision repair / In eukaryotes / Damage recognition / Global genomic NER (GG-NER)
caption_attribution_description: English: Cartoon depiction of global genomic repair, a subpathway of nucleotide excision repair.Shows the binding of involved proteins at various steps (XPC, HR23b, CAK, TFIIH, XPA, RPA, XPG, XPF, ERCC1, TFIIH, PCNA, RFC, ADN Pol, Ligase I).
context_page_description: Nucleotide excision repair is a DNA repair mechanism. DNA damage occurs constantly because of chemicals, radiation and other mutagens. Three excision repair pathways exist to repair single stranded DNA damage: Nucleotide excision repair, base excision repair, and DNA mismatch repair. While the BER pathway can recognize specific non-bulky lesions in DNA, it can correct only damaged bases that are removed by specific glycosylases. Similarly, the MMR pathway only targets mismatched Watson-Crick base pairs.
  Nucleotide excision repair is a particularly important excision mechanism that removes DNA damage induced by ultraviolet light. UV DNA damage results in bulky DNA adducts - these adducts are mostly thymine dimers and 6,4-photoproducts. Recognition of the damage leads to removal of a short single-stranded DNA segment that contains the lesion. The undamaged single-stranded DNA remains and DNA polymerase uses it as a template to synthesize a short complementary sequence. Final ligation to complete NER and form a double stranded DNA is carried out by DNA ligase. NER can be divided into two subpathways: global genomic NER and transcription coupled NER.
context_section_description: Global genomic NER repairs damage in both transcribed and untranscribed DNA strands in active and inactive genes throughout the genome. This process is not dependent on transcription. This pathway employs several "damage sensing" proteins including the DNA-damage binding (DDB) and XPC-Rad23B complexes that constantly scan the genome and recognize helix distortions: the XPC-Rad23B complex is responsible for distortion recognition, while DDB1 and DDB2 (XPE) can also recognize some types of damage caused by UV light. Additionally, XPA performs a function in damage recognition that is as yet poorly defined. Upon identification of a damaged site, subsequent repair proteins are then recruited to the damaged DNA to verify presence of DNA damage, excise the damaged DNA surrounding the lesion then fill in the repair patch.
caption: Schematic depicts binding of proteins involved with GG-NER.[3]
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