ERCC3 is a component of the core TFIIH basal transcription factor and functions as an ATP-dependent 3’-5’ DNA helicase. ERCC3 is involved in nucleotide excision repair and is the cause of xeroderma pigmentosum complementation group B (XPB), also known as xeroderma pigmentosum II (XP2). Additionally, it has been found to be the cuase of Cockayne syndrome, and trichothiodystrophy (TTD). XPB is an autosomal recessive disease characterized by skin photosensitivity and a predisposition to skin cancer, and neurological abnormalities. Cockayne syndrome and TTD are similarly characterized by photosensitivity and neural abnormalities.