XPB and XPD between transcription and DNA repair

Abstract

Xeroderma pigmentosum group B and D genes (XPB and XPD respectively) are components of the transcription factor IIH (TFIIH), a nine-subunit complex involved in transcription initiation by RNA polymerase II (pol II). Five of these (XPB, p62, p52, p44 and p34) form a tight core subcomplex, while XPD is less tightly associated with the core and mediates the binding of the CAK subcomplex, containing the remaining three subunits, cyclin H, cdk7 and MAT1.1,2 The TFIIH complex also plays a key role in nucleotide excision repair (NER) by opening duplex DNA at the damage site. Both XPB and XPD possess DNA helicase activities, though XPB functions in a 3 → 5 fashion,3 while XPD catalyzes unwinding of duplex DNA in the opposite direction.2 The DNA-dependent helicase activity of XPB and XPD is central to the function of TFIIH in both transcription initiation and NER. © 2009 Springer New York.