54336 bp; 23 exons

2400b mRNA

760 amino acids

ubiquitous

nuclear

5-3 ATP-dependent helicase activity involved in DNA excision repair (NER) and as a subunit of the basal transcription factor TFIIH
The XPD gene product displayed 5-3 helicase activity. The XPD as the XPB protein are also found in the transcription factor TFIIH, a large complex involved in the initiation of transcription The striking discovery that subunits of basal transcription factor TFIIH were involved in Nucleotide Excision Repair (NER) sheds light on a new aspect of NER : a close coupling to transcription via common use of essential factors. TFIIH fulfills a dual role in transcription initiation and NER and the role of TFIIH in NER might closely mimic its role in the transcription initiation process. In transcription initiation TFIIH is thought to be involved in unwinding of the promoter site and to allow promoter clearance. In the NER process TFIIH causes unwinding of the damage containing region that has been localized by XPC-HR23B and XPA-RPA, enabling the accumulation of NER proteins around the damaged site. Contrarely to the XPB helicase, the helicase activity of XPD is indispensable for NER but not for transcription initiation. So, there is much more XPD patients, and only two patients have been described as XP and CS.

FLYBASE :Xpd ; MGI : Ercc2 (Nb 95413)

17 mutated sites associated with the xeroderma pigmentosum group D syndrome (among them 3 are also associated with the Cockaynesyndrome) and 15 mutated sites associated with the trichothiodystrophy syndrome