NER mechanism. DNA damage removal by NER is roughly executed in four subsequent steps. First, damage is recognised during transcription by stalling of RNA polymerase and involving CSB (“transcription coupled”), or it is recognised throughout the rest of the genome by the UV-DDB and XPC/HR23B complexes (“global genome”). Upon recognition, the TFIIH complex is recruited to unwind DNA around the damage and structural proteins XPA and RPA bind the resulting single-stranded DNA. Next, endonucleases ERCC1/XPF and XPG excise a patch of DNA including the damage. Finally, gap filling by de novo DNA synthesis takes place. During processing of a lesions, other proteins in proximity, including histones, are modified as part of a signalling cascade.