Mechanism of open complex and dual incision formation by human nucleotide excision repair factors

• Published in: The EMBO journal Vol. 16; no. 21; pp. 6559 - 6573
• Main Authors: Evans, Elizabeth, Moggs, Jonathan G., Hwang, Jae R., Egly, Jean-Marc, Wood, Richard D.
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.11.1997
• Subjects: Adenosine Triphosphate - metabolism; Cells, Cultured; cisplatin; Cisplatin - pharmacology; DNA - drug effects; DNA - metabolism; DNA Damage; DNA Helicases - metabolism; DNA Ligases - metabolism; DNA repair; DNA Repair - physiology; DNA, Single-Stranded - metabolism; DNA-Binding Proteins - metabolism; Endonucleases; HeLa Cells; Humans; Macromolecular Substances; Models, Genetic; Nuclear Proteins; nucleases; Point Mutation; Proteins - metabolism; Replication Protein A; Substrate Specificity; TFIIH; Transcription Factor TFIIH; Transcription Factors - chemistry; Transcription Factors - metabolism; Transcription Factors, TFII; Transcription, Genetic; xeroderma pigmentosum; Xeroderma Pigmentosum - enzymology; Xeroderma Pigmentosum - genetics; Xeroderma Pigmentosum - pathology; Xeroderma Pigmentosum Group A Protein; Xeroderma Pigmentosum Group D Protein
• ISSN: 0261-4189; 1460-2075; 1460-2075
• DOI: 10.1093/emboj/16.21.6559

During nucleotide excision repair in human cells, a damaged DNA strand is cleaved by two endonucleases, XPG on the 3′ side of the lesion and ERCC1‐XPF on the 5′ side. These structure‐specific enzymes act at junctions between duplex and single‐stranded DNA. ATP‐dependent formation of an open DNA structure of ∼25 nt around the adduct precedes this dual incision. We investigated the mechanism of open complex formation and find that mutations in XPB or XPD, the DNA helicase subunits of the transcription and repair factor TFIIH, can completely prevent opening and dual incision in cell‐free extracts. A deficiency in XPC protein also prevents opening. The absence of RPA, XPA or XPG activities leads to an intermediate level of strand separation. In contrast, XPF or ERCC1‐defective extracts open normally and generate a 3′ incision, but fail to form the 5′ incision. This same repair defect was observed in extracts from human xeroderma pigmentosum cells with an alteration in the C‐terminal domain of XPB, suggesting that XPB has an additional role in facilitating 5′ incision by ERCC1‐XPF nuclease. These data support a mechanism in which TFIIH‐associated helicase activity and XPC protein catalyze initial formation of the key open intermediate, with full extension to the cleavage sites promoted by the other core nucleotide excision repair factors. Opening is followed by dual incision, with the 3′ cleavage made first.