The DNA damage in GG-NER is recognized by the joint action of two protein complexes. The first complex is composed of XPC, RAD23A or RAD23B and CETN2. The second complex, known as the UV-DDB complex, is an ubiquitin ligase composed of DDB1, CUL4A or CUL4B, RBX1 and a GG-NER specific protein DDB2. In vitro, the UV-DDB complex is onlynecessary for GG-NER mediated repair of UV-induced pyrimidine dimers. In vivo, however, where DNA repair occurs in the chromatin context, the UV-DDB complex likely facilitates GG-NER mediated repair irrespective of the DNA damage type.
After DNA damage recognition, the TFIIH complex, together with XPA, verifies the DNA damage and unwinds the DNA helix around the damage, creating an open bubble. Two DNA endonucleases, ERCC5 (XPG) and the complex of ERCC1 and ERCC4 (XPF), excise the oligonucleotide that contains damaged base(s) from the affected DNA strand. DNA polymerases delta, epsilon and/or kappa perform DNA repair synthesis, followed by DNA ligation, thus completing GG-NER.
For a recent review, please refer to Marteijn et al. 2014.