The Xeroderma Pigmentosum Group C Protein Complex XPC-HR23B Plays an Important Role in the Recruitment of Transcription Factor IIH to Damaged DNA

The xeroderma pigmentosum group C protein complex XPC-HR23B was first isolated as a factor that complemented nucleotide excision repair defects of XP-C cell extracts in vitro. Recent studies have revealed that this protein complex plays an important role in the early steps of global genome nucleotide excision repair, especially in damage recognition, open complex formation, and repair protein complex formation. However, the precise function of XPC-HR23B in global genome repair is still unclear. Here we demonstrate that XPC-HR23B interacts with general transcription factor IIH (TFIIH) both in vivo and in vitro. This interaction is thought to be mediated through the specific affinity of XPC for the TFIIH subunits XPB and/or p62, which are essential for both basal transcription and nucleotide excision repair. Interestingly, association of TFIIH with DNA was observed in both wild-type and XP-A cell extracts but not in XP-C cell extracts, and XPC-HR23B could restore the association of TFIIH with DNA in XP-C cell extracts. Moreover, we found that XPC-HR23B was necessary for efficient association of TFIIH with damaged DNA in cell-free extracts. We conclude that the XPC-HR23B protein complex plays a crucial role in the recruitment of TFIIH to damaged DNA in global genome repair.