After the XPC complex and the UV-DDB complex bind damaged DNA, a basal transcription factor TFIIH is recruited to the nucleotide excision repair (NER) site (Volker et al. 2001, Riedl et al. 2003). DNA helicases ERCC2 (XPD) and ERCC3 (XPB) are subunits of the TFIIH complex. ERCC2 unwinds the DNA around the damage in concert with the ATPase activity of ERCC3, creating an open bubble (Coin et al. 2007). Simultaneously, the presence of the damage is verified by XPA (Camenisch et al. 2006). The recruitment of XPA is partially regulated by PARP1 and/or PARP2 (King et al. 2012).
Two DNA endonucleases, ERCC5 (XPG) and the complex of ERCC1 and ERCC4 (XPF), are recruited to the open bubble structure to form the incision complex that will excise the damaged oligonucleotide from the affected DNA strand (Dunand-Sauthier et al. 2005, Zotter et al. 2006, Riedl et al. 2003, Tsodikov et al. 2007, Orelli et al. 2010). The RPA heterotrimer coats the undamaged DNA strand, thus protecting it from the endonucleolytic attack (De Laat et al. 1998).