High Quality Content by WIKIPEDIA articles! XPB (Xeroderma Pigmentosum B) is an ATP dependent human DNA helicase that is a part of the TFIIH transcription factor complex. THe 3D structure of the archeael homologue of XPB has been solved by X-ray crystallography by Dr. JOhn Tainer and his group at The Scripps Research Institute. XPB Plays a significant role in normal basal transcription, transcription coupled repair (TCR), and nucleotide excision repair (NER). PUrified XPB has been shown to unwind DNA with 3'-5'polarity. MUtations in XPB and other related complementation groups, XPA-XPG, leads to a number of genetic disorders such as Xeroderma Pigmentosum, Cockayne's syndrome, and Trichothiodystrophy.