Correction of xeroderma pigmentosum repair defect by basal transcription factor BTF2 (TFIIH).

Abstract

ERCC3 was initially identified as a gene correcting the nucleotide excision repair (NER) defect of xeroderma pigmentosum complementation group B (XP‐B). The recent finding that its gene product is identical to the p89 subunit of basal transcription factor BTF2(TFIIH), opened the possibility that it is not directly involved in NER but that it regulates the transcription of one or more NER genes. Using an in vivo microinjection repair assay and an in vitro NER system based on cell‐free extracts we demonstrate that ERCC3 in BTF2 is directly implicated in excision repair. Antibody depletion experiments support the idea that the p62 BTF2 subunit and perhaps the entire transcription factor function in NER. Microinjection experiments suggest that exogenous ERCC3 can exchange with ERCC3 subunits in the complex. Expression of a dominant negative K436‐‐>R ERCC3 mutant, expected to have lost all helicase activity, completely abrogates NER and transcription and concomitantly induces a dramatic chromatin collapse. These findings establish the role of ERCC3 and probably the entire BTF2 complex in transcription in vivo which was hitherto only demonstrated in vitro. The results strongly suggest that transcription itself is a critical component for maintenance of chromatin structure. The remarkable dual role of ERCC3 in NER and transcription provides a clue in understanding the complex clinical features of some inherited repair syndromes.

The Yeast TFB1 and SSL1 Genes, Which Encode Subunits of Transcription Factor IIH, Are Required for Nucleotide Excision Repair and RNA Polymerase II Transcription

“…By implication, the human genes that encode p62 protein (the Tfb1 homolog) and p44 protein (the Ssl1 homolog) are likely also required for NER. Immunodepletion studies with antibodies against p62 and p44 proteins inhibit in vitro NER in human cell extracts (13,25). However, the entire TFIIH complex was also depleted from the extracts in these studies.…”

“…Core TFIIH-Ssl2 is required for both transcription by RNA polymerase II and nucleotide excision repair (NER) in S. cerevisiae and humans (4,23,25,28). Consistent with their requirement for transcription, SSL2, RAD3, TFB1, and SSL1 are essential yeast genes (10-12, 17, 18, 34).…”

“…Homologous genes designated XPB, XPD, p62, and p44, respectively, encode subunits of TFIIH(BTF2) in human cells (4,7,13,19,20). Mutations in the XPB and XPD genes are associated with several human hereditary diseases, including xeroderma pigmentosum, xeroderma pigmentosum with Cockayne's syndrome, and trichothiodystrophy (1, 27).Core TFIIH-Ssl2 is required for both transcription by RNA polymerase II and nucleotide excision repair (NER) in S. cerevisiae and humans (4,23,25,28). Consistent with their requirement for transcription, SSL2, RAD3, TFB1, and SSL1 are essential yeast genes (10-12, 17, 18, 34).…”

Redundancy of DNA helicases in p53-mediated apoptosis

“…These findings were mainly derived from either the use of a microinjection approach or the use of DNA damaging agents that induce p53-mediated apoptosis. Microinjection techniques have been used extensively by us and other laboratories to study biological functions in primary cells (Weeda et al, 1990;van Vuuren et al, 1994;Attardi et al, 1996;Wang et al, 1996Wang et al, , 2001van Gool et al, 1997;Spillare et al, 1999;Winkler et al, 2000). As the SV-40T antigen can bind to and inactivate p53, our studies require the use of primary cells instead of SV-40 immortalized cells.…”

p53-mediated transcription induces resistance of DNA to UV inactivation

“…Five of the subunits of the mammalian core TFIIH factor, p89/XPB/ERCC3 (Schae er et al, 1993), XPD/ERCC2 , p62 , p34 and p44 , have been implicated in DNA excision repair activity as well as in transcription. It has been demonstrated that p53 binds to p62 (Xiao et al, 1994), p89/XPB/ERCC3 (Wang et al, 1994) and XPD/ERCC2 , components of the basal transcription and nucleotide excision repair factor TFIIH/BTF2 (Schae er et al, 1993;van Vuuren et al, 1994).…”