RESUMEN
Nucleotide excision repair (NER) removes damage from DNA in a tightly regulated multiprotein process. The xeroderma pigmentosum group B (XPB) helicase subunit of TFIIH functions in NER and transcription. The serine 751 (S751) residue of XPB was found to be phosphorylated in vivo. This phosphorylation inhibits NER and the microinjection of a phosphomimicking XPB-S751E mutant is unable to correct the NER defect of XP-B cells. Conversely, XPB-S751 dephosphorylation or its substitution with alanine (S751A) restores NER both in vivo and in vitro. Surprisingly, phospho/dephosphorylation of S751 spares TFIIH-dependent transcription. Finally, the phosphorylation of XPB-S751 does not impair the TFIIH unwinding of the DNA around the lesion, but rather prevents the 5' incision triggered by the ERCC1-XPF endonuclease. These data support an additional role for XPB in promoting the incision of the damaged fragment and reveal a point of NER regulation on TFIIH without interference in its transcription activity.
Asunto(s)
ADN Helicasas/metabolismo , Reparación del ADN , Proteínas de Unión al ADN/metabolismo , Factores de Transcripción TFII/metabolismo , Animales , Células CHO , Quinasa de la Caseína II/metabolismo , Células Cultivadas , Cricetinae , ADN/metabolismo , ADN Helicasas/genética , Proteínas de Unión al ADN/genética , Endonucleasas/genética , Endonucleasas/metabolismo , Fibroblastos/citología , Fibroblastos/fisiología , Humanos , Fosforilación , Mutación Puntual , Serina/metabolismo , Factor de Transcripción TFIIH , Factores de Transcripción TFII/genética , Transcripción GenéticaRESUMEN
Mutation in the CSB gene results in the human Cockayne's syndrome (CS). Here, we provide evidence that CSB is found not only in the nucleoplasm but also in the nucleolus within a complex (CSB IP/150) that contains RNA pol I, TFIIH, and XPG and promotes efficient rRNA synthesis. CSB is active in in vitro RNA pol I transcription and restores rRNA synthesis when transfected in CSB-deficient cells. We also show that mutations in CSB, as well as in XPB and XPD genes, all of which confer CS, disturb the RNA pol I/TFIIH interaction within the CSB IP/150. In addition to revealing an unanticipated function for CSB in rRNA synthesis, we show that the fragility of this complex could be one factor contributing to the CS phenotype.
Asunto(s)
ADN Helicasas/metabolismo , ARN Polimerasa I/metabolismo , Factores de Transcripción , Transcripción Genética , Western Blotting , Nucléolo Celular/metabolismo , Células Cultivadas , ADN Helicasas/deficiencia , ADN Helicasas/genética , Enzimas Reparadoras del ADN , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/metabolismo , Endonucleasas , Fibroblastos , Técnica del Anticuerpo Fluorescente , Humanos , Complejos Multienzimáticos/química , Complejos Multienzimáticos/metabolismo , Mutación , Proteínas Nucleares , Proteínas de Unión a Poli-ADP-Ribosa , Unión Proteica , Proteínas/genética , Proteínas/metabolismo , ARN Ribosómico/biosíntesis , Factor de Transcripción TFIIH , Factores de Transcripción TFII/metabolismo , Proteína de la Xerodermia Pigmentosa del Grupo DRESUMEN
To counteract the deleterious effects of genotoxic injury, cells have set up a sophisticated network of DNA repair pathways. We show that Gal4-VP16 and RAR transcriptional activators stimulate nucleotide excision repair (NER). This DNA repair activation is not coupled to transcription since it occurs in Cockayne syndrome cells (which are transcription-coupled repair deficient) and is observed in vitro in the presence of alpha-amanitin and in the absence of the basal transcription factors. Using a reconstituted dual incision assay, we also show that binding of activators to their cognate sequences induces a local chromatin remodeling mediated by ATP-driven chromatin remodeling and acetyltransferase activities to facilitate DNA repair.
Asunto(s)
Reparación del ADN/fisiología , ADN/metabolismo , Transactivadores/metabolismo , Transcripción Genética , Secuencia de Bases , Sitios de Unión , Línea Celular Transformada , ADN/química , Proteínas de Unión al ADN , Proteína Vmw65 de Virus del Herpes Simple/metabolismo , Humanos , Oligodesoxirribonucleótidos/química , Receptores de Ácido Retinoico/metabolismo , Proteínas Recombinantes de Fusión/metabolismo , Mapeo Restrictivo , Proteínas de Saccharomyces cerevisiae/metabolismo , Virus 40 de los Simios/genética , Moldes Genéticos , Factores de Transcripción/metabolismo , TransfecciónRESUMEN
In response to genotoxic attacks, cells activate sophisticated DNA repair pathways such as nucleotide excision repair (NER), which consists of damage removal via dual incision and DNA resynthesis. Using permanganate footprinting as well as highly purified factors, we show that NER is a dynamic process that takes place in a number of successive steps during which the DNA is remodeled around the lesion in response to the various NER factors. XPC/HR23B first recognizes the damaged structure and initiates the opening of the helix from position -3 to +6. TFIIH is then recruited and, in the presence of ATP, extends the opening from position -6 to +6; it also displaces XPC downstream from the lesion, thereby providing the topological structure for recruiting XPA and RPA, which will enlarge the opening. Once targeted by XPG, the damaged DNA is further melted from position -19 to +8. XPG and XPF/ERCC1 endonucleases then cut the damaged DNA at the limit of the opened structure that was previously "labeled" by the positioning of XPC/HR23B and TFIIH.