General transcription and DNA repair factor IIH helicase subunit XPD (ERCC2)

In NER, TFIIH acts by opening DNA around the lesion to enable the excision of the damaged oligonucleotide and its replacement by a new DNA fragment. The ATP-dependent helicase activity of XPD/ERCC2 is needed for DNA opening.

In transcription, TFIIH has an essential role in transcription initiation. When the pre- initiation complex (PIC) was established, TFIIH is required for promoter opening and promoter escape.