{"gene":"ERCC6","run_date":"2026-04-28T17:46:03","timeline":{"discoveries":[{"year":1992,"finding":"ERCC6/CSB encodes a 1493 amino acid protein containing seven consecutive helicase motifs (SWI2/SNF2 family) and is required for transcription-coupled nucleotide excision repair (TC-NER), specifically the preferential repair of lesions from the transcribed strand of active genes. Mutation analysis showed the gene is not essential for cell viability but is specific for preferential repair of transcribed sequences.","method":"Gene cloning, complementation of CS-B cells, mutation analysis of CS-B patient","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 — original cloning paper with complementation, mutation analysis, domain identification; foundational study replicated extensively","pmids":["1339317"],"is_preprint":false},{"year":1990,"finding":"ERCC6 gene was cloned by complementation of the UV-sensitive CHO mutant UV61 (rodent complementation group 6), which harbors a deficiency in repair of UV-induced cyclobutane pyrimidine dimers but shows apparently normal repair of (6-4) photoproducts. The gene spans ~115 kb of genomic DNA.","method":"Genomic DNA transfection, complementation cloning, Southern blot analysis","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 — original cloning by functional complementation with rigorous controls","pmids":["2172786"],"is_preprint":false},{"year":1993,"finding":"ERCC6 gene spans 82-90 kb, consists of at least 21 exons, contains seven distinct helicase signature domains encoded on separate exons, and produces two mRNA molecules of 5 and 7 kb via alternative polyadenylation.","method":"Genomic organization analysis, cDNA cloning, Northern blot","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 — direct genomic and cDNA structural analysis","pmids":["8382798"],"is_preprint":false},{"year":1997,"finding":"Purified recombinant human CSB/ERCC6 protein is a DNA-stimulated ATPase but is not a helicase and does not disrupt the ternary transcription complex of stalled RNA polymerase II. CSB binds DNA and also physically interacts with XPA, TFIIH, and the p34 subunit of TFIIE.","method":"Baculovirus overexpression, protein purification, ATPase assay, helicase assay, RNA pol II stalling/dissociation assay, direct binding assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro biochemical reconstitution with purified recombinant protein, multiple assays","pmids":["8999876"],"is_preprint":false},{"year":1997,"finding":"CSB/ERCC6 physically interacts with RNA polymerase II engaged in elongation ternary complexes containing DNA and nascent RNA, and this interaction requires ATP hydrolysis (the beta-gamma bond) to form a stable Pol II-CSB-DNA-RNA complex. CSA does not directly bind Pol II.","method":"Oligo(dC)-tailed DNA template biochemical assay, ATPase mutant analysis, binding assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with ternary complexes, mutagenesis of ATPase motif","pmids":["9372911"],"is_preprint":false},{"year":1996,"finding":"CSB/ERCC6 restores transcription-coupled repair of UV-induced cyclobutane pyrimidine dimers (CPDs) in the transcribed strand of the actively transcribed DHFR gene when transfected into the TCR-deficient CHO cell line UV61, demonstrating that CSB has an independent role in TCR separate from general RNA Pol II transcription.","method":"Transfection complementation, strand-specific repair assay (gene-specific repair assay), CPD measurement","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 — functional complementation with defined molecular readout in cell-based system","pmids":["8811084"],"is_preprint":false},{"year":2000,"finding":"Transcription-coupled repair of 8-oxoguanine requires CSB (as well as XPG and TFIIH). CS-B cells not only lack TCR of 8-oxoG but cannot remove 8-oxoG from a transcribed sequence despite proficient repair elsewhere; unrepaired 8-oxoG blocks RNA polymerase II transcription and leads to a mutation frequency of 30-40% vs normal 1-4%.","method":"Strand-specific repair assay, mutation frequency analysis, CS cell lines vs. normal human cells and XP cells","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 — cell-based genetic analysis with multiple CS and XP cell lines, quantitative readouts","pmids":["10786832"],"is_preprint":false},{"year":2002,"finding":"CSB is a component of a nucleolar 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. CS-causing mutations in CSB (as well as XPB and XPD) disrupt the RNA pol I/TFIIH interaction within this complex.","method":"Immunoprecipitation, in vitro RNA pol I transcription assay, transfection complementation, immunofluorescence (nucleolar localization)","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro transcription reconstitution plus complementation and complex characterization","pmids":["12419226"],"is_preprint":false},{"year":2004,"finding":"GFP-tagged CSB, expressed at physiological levels, is homogeneously dispersed in the nucleoplasm plus bright nuclear foci and nucleolar accumulation. FRAP studies showed GFP-CSB transiently interacts with the transcription elongation machinery as part of a high-molecular-weight complex; upon UV-induced transcription arrest, CSB binding to these complexes is prolonged, consistent with engagement in TC-NER.","method":"GFP tagging, live-cell imaging, FRAP (fluorescence recovery after photobleaching)","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — direct live-imaging with quantitative FRAP showing functional state-dependent dynamics","pmids":["15226310"],"is_preprint":false},{"year":2004,"finding":"CSB actively wraps DNA around itself in an ATP-dependent manner: scanning force microscopy showed DNA contour length shortening upon CSB binding, consistent with DNA wrapping. Non-hydrolyzable ATP analogues increased the frequency of shorter DNA molecules, suggesting ATP binding promotes wrapping and ATP hydrolysis causes unwrapping. CSB likely binds DNA as a dimer.","method":"Scanning force microscopy, ATP and non-hydrolyzable ATP analogue comparison","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — direct structural/biophysical characterization with multiple conditions","pmids":["15548521"],"is_preprint":false},{"year":2006,"finding":"CSB is a substrate of the CSA-containing E3 ubiquitin ligase complex: following UV irradiation, CSB is ubiquitinated and degraded by the proteasome in a CSA-dependent manner at a late stage of TC-NER. CSB degradation is required for post-TCR recovery of transcription.","method":"Ubiquitination assays, proteasome inhibition, CSA-deficient cells, RNA synthesis recovery assay","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (biochemical, genetic, functional) in a single study","pmids":["16751180"],"is_preprint":false},{"year":2010,"finding":"UV-induced stable association of CSB with chromatin requires ATP hydrolysis. The N-terminal region of CSB negatively autoregulates chromatin association during normal growth, and ATP hydrolysis is required to overcome this inhibitory effect. Mutations causing Cockayne syndrome can underlie defects in this chromatin association mechanism.","method":"Chromatin fractionation, ATPase mutant analysis, deletion mapping of N-terminal region, UV treatment","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 — multiple mutants and conditions with direct chromatin fractionation readout","pmids":["20122405"],"is_preprint":false},{"year":2003,"finding":"Mutations in conserved ATPase motifs II, V, and VI of CSB differentially reduce ATPase activity, and dephosphorylation of CSB in vitro results in increased ATPase activity. UV irradiation leads to CSB dephosphorylation in cells, suggesting that phosphorylation status regulates CSB ATPase activity in vivo.","method":"Site-directed mutagenesis of helicase motifs, in vitro ATPase assay, phosphorylation analysis","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 — in vitro biochemical assay with mutagenesis and biochemical regulation","pmids":["12560492"],"is_preprint":false},{"year":2012,"finding":"UVSSA protein forms a complex with USP7, stabilizes ERCC6/CSB protein levels, and restores the hypophosphorylated form of RNA pol II after UV irradiation. Mutations in UVSSA cause UV-sensitive syndrome by destabilizing CSB.","method":"Microcell-mediated chromosome transfer (gene cloning), co-immunoprecipitation, complementation assay, western blot for CSB stability","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 — gene cloning by functional approach, Co-IP, complementation, protein stability assays","pmids":["22466612"],"is_preprint":false},{"year":2017,"finding":"CSB displays strong affinity for DNA:RNA hybrids in vitro and acts as a sensor of ROS-induced R loops in transcribed regions. During transcription-coupled homologous recombination (TC-HR), CSB is recruited by R loops, then recruits RAD52 through an acidic domain of CSB, and the CSB-RAD52-RAD51 axis carries out a BRCA1/2-independent alternative HR pathway protecting the transcribed genome.","method":"In vitro DNA:RNA hybrid binding assay, ROS-induced R loop induction, laser microirradiation with fluorescent protein foci assay, epistasis with RAD52/BRCA1/BRCA2 knockdown","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — in vitro binding plus cell-based epistasis and imaging with multiple orthogonal approaches","pmids":["30297739"],"is_preprint":false},{"year":2017,"finding":"ATM-dependent phosphorylation of CSB on S10 and CDK2-dependent phosphorylation on S158 are required for CSB's chromatin remodeling activity at DSBs. CSB interacts via its winged helix domain (WHD) with RIF1, and this interaction mediates CSB recruitment to DSBs in S phase. At DSBs, CSB remodels chromatin by evicting histones, which limits RIF1 and MAD2L2 accumulation but promotes BRCA1 accumulation, thereby regulating DSB repair pathway choice.","method":"Co-IP, phospho-specific mutant analysis, chromatin immunoprecipitation, histone eviction assay, DSB repair pathway choice analysis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods defining post-translational modifications and interaction domains with functional readouts","pmids":["29203878"],"is_preprint":false},{"year":2019,"finding":"CSB interacts with the BRCT domain of BRCA1 in a CDK-dependent manner (phosphorylation on S1276), peaking in late S/G2 phase. This interaction mediates CSB's association with the BRCA1-C complex (BRCA1, MRN, CtIP). CSB phosphorylation on S1276 promotes MRN- and CtIP-mediated DNA end resection for HR and restricts NHEJ, while being dispensable for histone eviction at DSBs.","method":"Co-IP, CDK inhibitor treatment, phospho-mutant analysis, DNA end resection assay, cell survival assay","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, phospho-mutant analysis, epistasis, multiple readouts","pmids":["31501894"],"is_preprint":false},{"year":2018,"finding":"CSB stimulates recruitment of XRCC1 (a BER-scaffolding protein) to 8-oxoG lesions in a transcription-dependent manner. OGG1 recruitment to 8-oxoG is independent of CSB. XRCC1 recruitment to BER-unrelated single-strand breaks does not require CSB, suggesting CSB specifically facilitates BER progression at transcribed genes by recruiting XRCC1 to BER-generated SSBs masked by stalled RNA polymerase II.","method":"Live-cell imaging with laser-assisted local induction of 8-oxoG, fluorescent protein recruitment kinetics, CSB knockdown and knockout cells","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 — quantitative live imaging with multiple conditions and controls","pmids":["29955842"],"is_preprint":false},{"year":2021,"finding":"CSB loads the PAF1 complex (PAF1C) onto RNA polymerase II in promoter-proximal regions in response to DNA damage. PAF1C is dispensable for TCR-mediated repair but is essential for transcription recovery after UV irradiation by promoting RNAPII pause release in promoter-proximal regions and acting as a processivity factor for transcription elongation throughout genes.","method":"Co-IP, ChIP-seq, mass spectrometry, RNA recovery assays after UV, PAF1C knockdown, UV survival","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal approaches defining a new molecular pathway with clear functional readouts","pmids":["33637760"],"is_preprint":false},{"year":2024,"finding":"CSB and CSA are required for transcription-coupled DNA-protein crosslink (DPC) repair in actively transcribed genes. DPC formation arrests transcription, and CSB/CSA-deficient cells fail to efficiently restart transcription after DPC induction. Downstream TC-NER factors (XPA etc.) are dispensable, indicating a non-canonical TC-NER mechanism for DPCs. TC-DPC repair is mediated by the ubiquitin ligase CRL4CSA and the proteasome.","method":"DPC sequencing (genome-wide DPC mapping), genetic screens, transcription restart assays, cell survival assays, epistasis with NER factors","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 — genome-wide mapping plus genetic and biochemical epistasis in two independent concurrent studies","pmids":["38600235","38600236"],"is_preprint":false},{"year":2008,"finding":"CSB expression is directly regulated by HIF-1; CSB mutant cells fail to properly activate the HIF-1 pathway under hypoxia. CSB redistributes p300 between HIF-1 and p53, functioning in a feedback loop that modulates p53 biological functions during hypoxic response.","method":"Reporter assays, ChIP, co-immunoprecipitation, CSB-deficient cell analysis, HIF-1 pathway activation assays","journal":"The EMBO journal","confidence":"Medium","confidence_rationale":"Tier 2 — multiple methods but single lab","pmids":["18784753"],"is_preprint":false},{"year":2011,"finding":"CSB and CSA associate in a unique complex with p53 and Mdm2 (a Cullin Ring Ubiquitin Ligase complex), and this interaction greatly stimulates Mdm2-dependent ubiquitination of p53. Absence of CSB leads to elevated and persistent p53 levels due to insufficient ubiquitination.","method":"Co-IP, tandem affinity purification, mass spectrometry, ubiquitination assays, CS patient cell analysis","journal":"Cell cycle","confidence":"Medium","confidence_rationale":"Tier 2 — TAP/MS plus Co-IP and functional ubiquitination assays, single lab","pmids":["22032989"],"is_preprint":false},{"year":2014,"finding":"CSB directly interacts with SNM1A (a 5'-3' exonuclease), modulates SNM1A's exonuclease activity on oligonucleotide substrates in vitro, and co-exists with SNM1A in a common complex in human cell extracts. Both proteins are recruited to trioxsalen-induced interstrand crosslink (ICL) damage in transcription-dependent manner; SNM1A recruitment is reduced in CSB-deficient cells. CSB-deficient neural cells show increased sensitivity to crosslinking agents and delayed ICL processing.","method":"Yeast two-hybrid, purified recombinant protein interaction, in vitro exonuclease assay, Co-IP from cell extracts, laser microirradiation + fluorescence microscopy, comet assay, γ-H2AX foci","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro reconstitution plus cell-based imaging and functional assays, multiple orthogonal methods","pmids":["25505141"],"is_preprint":false},{"year":2016,"finding":"VCP/p97 segregase mediates UV-induced ubiquitin-mediated CSB degradation. VCP/p97 interacts with both native and ubiquitin-conjugated forms of CSB, and VCP/p97 cofactors UFD1 and UBXD7 are required for CSB degradation. VCP/p97 associates with the CSA-DDB1-Cul4A E3 ligase complex. Inhibition of VCP/p97 causes accumulation of ubiquitinated CSB in chromatin and unexpectedly enhances recovery of RNA synthesis following UV.","method":"Co-IP, VCP/p97 inhibitors, siRNA depletion, localized UV irradiation with foci analysis, RNA synthesis recovery assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal Co-IP and multiple genetic/pharmacological perturbations, single lab","pmids":["26826127"],"is_preprint":false},{"year":2017,"finding":"NAP1L1 histone chaperone interacts with CSB and enhances CSB-mediated nucleosome remodeling. Single-molecule analysis showed CSB remodels nucleosomes via three phases (activation, translocation, pausing), and NAP1L1 accelerates both activation and translocation phases and decreases pausing probability, thereby increasing processivity.","method":"Single-molecule FRET/fluorescence microscopy, ATPase assay, in vitro nucleosome remodeling assay","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 — single-molecule real-time analysis with reconstituted nucleosomes","pmids":["28369616"],"is_preprint":false},{"year":2014,"finding":"A conserved 'leucine latch' motif at the N terminus of Rhp26 (S. pombe ortholog of CSB/ERCC6) mediates autoinhibition of ATPase and chromatin-remodeling activities via interaction with the core ATPase domain. The C terminus counteracts this autoinhibition; both N- and C-terminal regions are needed for proper DNA repair function in vivo.","method":"Mutagenesis, in vitro ATPase assay, nucleosome remodeling assay, in vivo DNA repair assay, protein interaction studies","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — reconstitution, mutagenesis, and in vivo complementation; conserved leucine latch also present in human CSB","pmids":["25512493"],"is_preprint":false},{"year":2020,"finding":"ROS-induced DNA damage at telomeres triggers R-loop accumulation in a TERRA- and TRF2-dependent manner. CSB and RAD52 are recruited to telomeric R-loops; RAD52 is recruited through interactions with both CSB and DNA:RNA hybrids. Both CSB and RAD52 are required for efficient repair of ROS-induced telomeric DSBs through a CSB-RAD52-POLD3-mediated break-induced replication pathway.","method":"Live-cell imaging, ChIP, immunoprecipitation, knockdown of CSB/RAD52/POLD3, R-loop detection (S9.6 antibody), comet assay","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods with clear epistasis","pmids":["31777915"],"is_preprint":false},{"year":2020,"finding":"CSB promotes recruitment of HR repair proteins (MRN, BRCA1, BLM, RPA32) and POLD3 to ALT telomeres via its ATPase activity (controlled by ATM- and CDK2-dependent phosphorylation). Loss of CSB stimulates telomeric recruitment of MUS81 and SLX4 (MUS-SLX endonuclease complex), suggesting CSB restricts MUS-SLX-mediated processing of stalled forks at ALT telomeres.","method":"Fluorescence imaging with tagged proteins, phospho-mutant analysis, epistasis with SMARCAL1 depletion, ATM/CDK2 inhibitor treatment","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 — cell-based imaging with multiple conditions, single lab","pmids":["31974116"],"is_preprint":false},{"year":2023,"finding":"CSB regulates PARP1- and PARP2-mediated single-strand break repair (SSBR) at actively transcribed DNA regions. PARP1 and PARP2 promote CSB recruitment to oxidatively-damaged DNA; CSB in turn promotes XRCC1 and HPF1 recruitment and histone PARylation. CSB's function in SSBR is bypassed when transcription is inhibited, showing CSB-mediated SSBR occurs primarily at actively transcribed regions.","method":"Chromatin co-fractionation, alkaline comet assay, transcription inhibition, siRNA depletion, immunofluorescence","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 — multiple biochemical and cell-based approaches, single lab","pmids":["37326017"],"is_preprint":false},{"year":2008,"finding":"CSB gene contains a domesticated PiggyBac-like transposon (PGBD3) in intron 5 that functions as an alternative 3' terminal exon, producing a CSB-PGBD3 fusion protein by alternative splicing of CSB exons 1–5 to the PGBD3 transposase. This fusion protein is as abundant as CSB protein in various human cell lines and continues to be expressed in CS cells with mutations beyond exon 5.","method":"RT-PCR, western blot, expression analysis in multiple cell lines, evolutionary conservation analysis","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 2 — multiple methods documenting expression and evolutionary conservation","pmids":["18369450"],"is_preprint":false},{"year":2015,"finding":"CSB mutant (CS patient) cells, but not UVSS cells, show depletion of mitochondrial DNA polymerase-γ catalytic subunit (POLG1) due to CSA/CSB-dependent accumulation of HTRA3 serine protease. Inhibition of serine proteases restored POLG1 levels in CS fibroblasts. CS cells showed greater nitroso-redox imbalance and altered mitochondrial oxidative phosphorylation compared to UVSS cells.","method":"Western blot, siRNA depletion of CSB, serine protease inhibitors, ROS scavengers, mitochondrial OXPHOS measurement","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 — multiple pharmacological and genetic tools with biochemical readouts, single lab","pmids":["26038566"],"is_preprint":false},{"year":2015,"finding":"CSB directly interacts with CTCF in vitro, and oxidative stress enhances the CSB-CTCF interaction in cells. CSB facilitates CTCF-DNA interactions in vitro and regulates CTCF-chromatin interactions in oxidatively stressed cells. Oxidative stress alters CSB's genomic occupancy and increases CSB occupancy at promoters, with CTCF regulating sites of CSB occupancy.","method":"ChIP-seq, in vitro protein interaction assay, co-IP from cells, oxidative stress treatment","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro direct interaction plus ChIP-seq and co-IP, single lab","pmids":["26578602"],"is_preprint":false},{"year":2024,"finding":"Cryo-EM structures of yeast Pol II-Rad26 complexes (ortholog of CSB) show that Rad26 uses a common mechanism to recognize stalled Pol II, with additional interactions when Pol II is arrested at a DNA lesion. Elf1 (ortholog of human ELOF1) induces further interactions between Rad26 and lesion-arrested Pol II. Biochemical and genetic data show that interplay between Elf1 and Rad26 is important for TC-NER initiation.","method":"Cryo-EM structure determination, biochemical assays, genetic analysis in yeast","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM structures with biochemical and genetic validation","pmids":["38194460"],"is_preprint":false},{"year":1994,"finding":"RAD26, the S. cerevisiae ortholog of ERCC6/CSB, is required for preferential TCR of UV-induced cyclobutane pyrimidine dimers from the transcribed strand of the active RBP2 gene. Disruption of RAD26 does not cause UV sensitivity (unlike human CSB mutations), indicating TCR in lower eukaryotes is not critical for cell survival.","method":"Gene cloning, RAD26 disruption mutant, strand-specific repair assay, UV/cisplatin/X-ray sensitivity testing","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — genetic complementation and strand-specific repair assay in yeast ortholog","pmids":["7957102"],"is_preprint":false},{"year":1996,"finding":"Purified yeast Rad26 protein (ortholog of human CSB) is a DNA-dependent ATPase that is much more active and strictly DNA-dependent compared to the E. coli Mfd protein, suggesting Rad26 may displace stalled RNA pol II or recruit repair components at DNA lesions.","method":"Yeast protein purification, in vitro ATPase assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — purified protein biochemical reconstitution","pmids":["8702468"],"is_preprint":false},{"year":2002,"finding":"Yeast Def1 forms a complex with Rad26 (CSB ortholog) in chromatin. In response to DNA damage, Rad26 promotes TCR while Def1 is required for ubiquitination and degradation of stalled RNA polymerase II (RNAPII) when lesions cannot be rapidly removed, providing a coordinated rescue mechanism for Pol II stalled at DNA lesions.","method":"Protein complex identification, genetic analysis, RNAPII ubiquitination assay, chromatin fractionation","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — protein complex identification plus genetic and biochemical characterization of RNAPII degradation","pmids":["11859374"],"is_preprint":false},{"year":2006,"finding":"CSB plays a general role in chromatin maintenance and remodeling: genes regulated by CSB overlap significantly with genes affected by HDAC inhibitors, DNA methylation inhibitors, PARP inhibitors, and RNA pol II elongation inhibitors. CSB-null cells are sensitive to HDAC and PARP inhibitors, indicating CSB has broad chromatin maintenance functions beyond TC-NER.","method":"Expression microarrays, comparative L2L analysis, drug sensitivity assays (HDAC and PARP inhibitors)","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2–3 — transcriptomic plus pharmacological sensitivity, indirect mechanistic evidence","pmids":["16772382"],"is_preprint":false}],"current_model":"ERCC6/CSB is an ATP-dependent SWI2/SNF2-family chromatin remodeler and DNA-stimulated ATPase that initiates transcription-coupled nucleotide excision repair (TC-NER) by recognizing RNA polymerase II stalled at DNA lesions—requiring ATP hydrolysis for stable chromatin association (regulated by N-terminal autoinhibition, ATM/CDK2-dependent phosphorylation, and CSA-mediated ubiquitin-proteasomal degradation after repair)—and additionally functions in RNA pol I transcription, base excision repair at transcribed regions (recruiting XRCC1 via PARP1/2), transcription-coupled DPC repair, BRCA1/2-independent homologous recombination at R-loops, DSB repair pathway choice (chromatin remodeling to promote HR over NHEJ), and telomere maintenance in ALT cells, while also loading PAF1C onto RNAPII to restore transcription elongation genome-wide after genotoxic stress."},"narrative":{"teleology":[{"year":1990,"claim":"Cloning of ERCC6 by functional complementation of the UV-sensitive CHO mutant UV61 established that a single gene corrects a specific deficiency in cyclobutane pyrimidine dimer repair, linking ERCC6 to a distinct DNA repair pathway.","evidence":"Genomic DNA transfection and complementation cloning in CHO UV61 cells","pmids":["2172786"],"confidence":"High","gaps":["No protein product characterized","Mechanism of repair deficiency unknown","Human disease connection not yet established"]},{"year":1992,"claim":"Full-length cloning and characterization of the ERCC6/CSB protein revealed SWI2/SNF2-family helicase motifs and demonstrated that CSB is specifically required for transcription-coupled NER — the preferential repair of lesions on the transcribed strand of active genes — establishing the molecular identity of the Cockayne syndrome group B gene.","evidence":"cDNA cloning, complementation of CS-B patient cells, domain analysis, mutation identification","pmids":["1339317"],"confidence":"High","gaps":["Biochemical activity of the protein unknown","Mechanism of coupling to transcription unclear"]},{"year":1994,"claim":"Identification of RAD26 as the yeast ortholog of ERCC6 confirmed that transcription-coupled repair is an evolutionarily conserved pathway, though dispensability for UV survival in yeast suggested additional functions in mammals.","evidence":"Gene disruption and strand-specific repair assay in S. cerevisiae","pmids":["7957102"],"confidence":"High","gaps":["Why yeast tolerates loss of TCR while human cells do not","Direct protein activity of Rad26 not yet measured"]},{"year":1997,"claim":"Biochemical reconstitution resolved the paradox of CSB's helicase motifs: CSB is a DNA-stimulated ATPase but not a helicase, and it physically interacts with elongating RNA polymerase II in an ATP-hydrolysis-dependent manner, establishing the mechanism of TC-NER initiation.","evidence":"Purified recombinant CSB — ATPase, helicase, and Pol II ternary complex binding assays with ATPase mutants","pmids":["8999876","9372911"],"confidence":"High","gaps":["Whether CSB remodels chromatin directly","How ATP hydrolysis stabilizes the Pol II interaction structurally"]},{"year":2000,"claim":"Demonstration that CSB is required for transcription-coupled repair of 8-oxoguanine expanded CSB's substrate repertoire beyond UV-induced CPDs to oxidative base lesions, explaining why CS patients exhibit features beyond UV sensitivity.","evidence":"Strand-specific repair and mutation frequency assays in CS-B cell lines","pmids":["10786832"],"confidence":"High","gaps":["Whether CSB recruits BER factors or only initiates TCR at oxidative lesions","Mechanism of Pol II stalling at 8-oxoG"]},{"year":2002,"claim":"Discovery that CSB resides in a nucleolar complex with RNA Pol I, TFIIH, and XPG and promotes rRNA synthesis revealed that CSB functions extend beyond DNA repair to active transcription by RNA polymerase I.","evidence":"Immunoprecipitation, in vitro RNA Pol I transcription, complementation in CSB-deficient cells","pmids":["12419226"],"confidence":"High","gaps":["Whether CSB remodels rDNA chromatin directly","Contribution to Cockayne syndrome neurodegeneration"]},{"year":2004,"claim":"Biophysical studies established that CSB wraps DNA around itself in an ATP-dependent manner and transiently associates with the transcription elongation machinery, with UV damage prolonging this association — defining CSB as a bona fide chromatin remodeler acting at sites of transcription arrest.","evidence":"Scanning force microscopy of DNA-CSB complexes and live-cell FRAP of GFP-CSB","pmids":["15548521","15226310"],"confidence":"High","gaps":["Nucleosome substrate remodeling not yet directly shown","No structural model of CSB on chromatin"]},{"year":2006,"claim":"Identification of CSB as a substrate of the CSA-containing CRL4 E3 ubiquitin ligase resolved how TC-NER is terminated: UV-induced ubiquitination and proteasomal degradation of CSB is required for post-repair transcription recovery.","evidence":"Ubiquitination assays, proteasome inhibition, CSA-deficient cells, RNA synthesis recovery","pmids":["16751180"],"confidence":"High","gaps":["Identity of the ubiquitin chain type on CSB","How CSB degradation timing is controlled"]},{"year":2010,"claim":"Mapping of an N-terminal autoinhibitory domain that restricts CSB's chromatin association during normal growth, overcome by ATP hydrolysis upon UV damage, provided a regulatory mechanism ensuring CSB activation is lesion-dependent.","evidence":"Chromatin fractionation with ATPase and N-terminal deletion mutants","pmids":["20122405"],"confidence":"High","gaps":["Structural basis of autoinhibition in human CSB","Whether post-translational modifications regulate autoinhibition"]},{"year":2012,"claim":"Discovery that UVSSA-USP7 stabilizes CSB protein levels explained how CSB abundance is maintained during repair and identified UVSSA mutations as the cause of UV-sensitive syndrome, distinguishing it from Cockayne syndrome.","evidence":"Complementation cloning, co-immunoprecipitation, CSB stability western blots","pmids":["22466612"],"confidence":"High","gaps":["Precise ubiquitin editing mechanism on CSB by USP7","Whether UVSSA modulates CSB activity beyond stabilization"]},{"year":2014,"claim":"Characterization of a conserved 'leucine latch' motif in the CSB ortholog Rhp26 defined the structural basis of N-terminal autoinhibition of ATPase and remodeling activity, with the C-terminus serving as a counterbalance — a mechanism conserved to human CSB.","evidence":"Mutagenesis, in vitro ATPase and nucleosome remodeling, in vivo complementation in S. pombe","pmids":["25512493"],"confidence":"High","gaps":["Direct demonstration of leucine-latch mechanism in human CSB","Allosteric coupling mechanism between termini and ATPase domain"]},{"year":2017,"claim":"Three contemporaneous studies expanded CSB's functions to DSB repair pathway choice and R-loop-dependent homologous recombination: ATM/CDK2-dependent phosphorylation drives CSB's chromatin remodeling at DSBs to evict histones and promote HR over NHEJ, while CSB senses R-loops and recruits RAD52 for BRCA1/2-independent HR, and NAP1L1 enhances CSB nucleosome remodeling processivity.","evidence":"Phospho-mutant analysis with histone eviction assays; in vitro DNA:RNA hybrid binding with epistasis; single-molecule FRET nucleosome remodeling","pmids":["29203878","30297739","28369616"],"confidence":"High","gaps":["Whether CSB-RAD52 HR operates at non-telomeric loci genome-wide","Structural basis of CSB recognition of R-loops versus naked DNA"]},{"year":2018,"claim":"Live-cell imaging demonstrated that CSB specifically recruits XRCC1 to 8-oxoG lesions in a transcription-dependent manner, establishing CSB as a bridge between stalled Pol II and downstream BER completion at transcribed genes.","evidence":"Laser-induced 8-oxoG with fluorescent XRCC1/OGG1 recruitment kinetics in CSB-KO cells","pmids":["29955842"],"confidence":"High","gaps":["Whether CSB physically contacts XRCC1 or acts indirectly through chromatin remodeling","Full BER intermediate processing at stalled Pol II sites"]},{"year":2019,"claim":"CDK-dependent phosphorylation of CSB at S1276 mediates interaction with BRCA1-BRCT domain, promoting MRN/CtIP-mediated end resection for HR at DSBs — separating CSB's resection-promoting function from its histone-eviction activity.","evidence":"Phospho-mutant co-IP, CDK inhibitor treatment, end resection assays","pmids":["31501894"],"confidence":"High","gaps":["Whether S1276 phosphorylation and S10/S158 phosphorylation are coordinated temporally","Structural basis of CSB-BRCA1 BRCT interaction"]},{"year":2020,"claim":"CSB was shown to operate at telomeres in ALT cells, where it recruits RAD52 and POLD3 for break-induced replication at R-loop-containing telomeric DSBs, extending CSB's R-loop repair function to telomere maintenance.","evidence":"ChIP, live-cell imaging, epistasis with CSB/RAD52/POLD3 knockdown, S9.6 R-loop detection at telomeres","pmids":["31777915","31974116"],"confidence":"High","gaps":["Whether CSB is required for ALT telomere maintenance in vivo (animal model)","Mechanism distinguishing telomeric from genomic R-loop repair"]},{"year":2021,"claim":"Discovery that CSB loads PAF1C onto RNAPII at promoter-proximal regions after DNA damage resolved how transcription restarts genome-wide after genotoxic stress — PAF1C is dispensable for repair itself but essential for elongation recovery.","evidence":"Co-IP, ChIP-seq, mass spectrometry, RNA recovery assays, PAF1C knockdown","pmids":["33637760"],"confidence":"High","gaps":["Whether CSB-PAF1C loading is specific to UV or general across damage types","Structural basis of CSB-PAF1C-RNAPII assembly"]},{"year":2023,"claim":"CSB was placed downstream of PARP1/2 signaling at oxidatively damaged transcribed DNA, where it promotes XRCC1, HPF1 recruitment and histone PARylation for single-strand break repair — a function bypassed when transcription is inhibited.","evidence":"Chromatin co-fractionation, alkaline comet assay, transcription inhibition, siRNA in human cells","pmids":["37326017"],"confidence":"Medium","gaps":["Direct physical interaction between CSB and PARP1/2 not demonstrated with purified proteins","Whether HPF1 recruitment is CSB-dependent or PARP-dependent"]},{"year":2024,"claim":"Cryo-EM structures of yeast Pol II-Rad26 complexes and functional studies of transcription-coupled DPC repair established the structural basis of CSB/Rad26 recognition of stalled Pol II, and expanded CSB's repair substrates to DNA-protein crosslinks via a non-canonical TC-NER mechanism requiring CRL4^CSA and the proteasome.","evidence":"Cryo-EM structures with biochemical/genetic validation (yeast); DPC-seq, genetic epistasis, transcription restart assays (human)","pmids":["38194460","38600235","38600236"],"confidence":"High","gaps":["No cryo-EM structure of human CSB-Pol II complex","DPC substrate specificity and size limits for TC-DPC repair unknown"]},{"year":null,"claim":"A high-resolution structure of human CSB engaged with Pol II on nucleosomal DNA, the precise allosteric mechanism linking autoinhibition relief to lesion-dependent activation, and how CSB's multiple repair and transcription functions are coordinated in time and space in vivo remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No human CSB-Pol II cryo-EM structure","In vivo single-molecule dynamics of CSB at different damage types not resolved","How CSB chooses between TC-NER, TC-BER, TC-HR, and TC-DPC repair pathways at a given lesion"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[3,4,9,12,34]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[3,9,14]},{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[14]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[24,25]}],"localization":[{"term_id":"GO:0005654","term_label":"nucleoplasm","supporting_discovery_ids":[8,11]},{"term_id":"GO:0005730","term_label":"nucleolus","supporting_discovery_ids":[7,8]},{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[11,15]}],"pathway":[{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[0,1,5,6,17,19,22,28,32,33]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[7,18]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[15,24,25,36]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[7,18]}],"complexes":["CSA-DDB1-CUL4A E3 ligase complex","RNA Pol I/TFIIH/XPG nucleolar complex","UVSSA-USP7 complex"],"partners":["ERCC8","UVSSA","RAD52","BRCA1","XRCC1","XPA","RIF1","SNM1A"],"other_free_text":[]},"mechanistic_narrative":"ERCC6/CSB is an ATP-dependent SWI2/SNF2-family chromatin remodeler that serves as a master coordinator of transcription-coupled DNA repair and transcription recovery at sites of RNA polymerase stalling. CSB is a DNA-stimulated ATPase (not a helicase) that wraps DNA in an ATP-dependent manner, physically associates with elongating RNA polymerase II through ATP hydrolysis, and is recruited to stalled polymerases at UV-induced lesions, oxidative damage (8-oxoguanine), interstrand crosslinks, and DNA-protein crosslinks to initiate transcription-coupled nucleotide excision repair and transcription-coupled base excision repair [PMID:1339317, PMID:8999876, PMID:9372911, PMID:10786832, PMID:38600235, PMID:29955842]. Its chromatin association is autoinhibited by an N-terminal region and activated by ATP hydrolysis and phosphorylation (ATM on S10, CDK2 on S158, CDK on S1276), enabling functions beyond TC-NER including histone eviction at DSBs to promote HR over NHEJ, BRCA1/2-independent homologous recombination at R-loops via RAD52 recruitment, telomere maintenance in ALT cells, RNA polymerase I-dependent rRNA synthesis, and PAF1C loading onto RNAPII for post-damage transcription restart [PMID:20122405, PMID:29203878, PMID:30297739, PMID:31501894, PMID:12419226, PMID:33637760]. CSB is regulated by CSA-DDB1-CUL4A E3 ligase-mediated ubiquitination and VCP/p97-dependent proteasomal degradation after repair completion, and is stabilized by the UVSSA-USP7 complex; loss-of-function mutations cause Cockayne syndrome, a multisystem disorder of defective transcription-coupled repair [PMID:16751180, PMID:22466612, PMID:26826127]."},"prefetch_data":{"uniprot":{"accession":"Q03468","full_name":"DNA excision repair protein ERCC-6","aliases":["ATP-dependent helicase ERCC6","Cockayne syndrome protein CSB"],"length_aa":1493,"mass_kda":168.4,"function":"Essential factor involved in transcription-coupled nucleotide excision repair (TC-NER), a process during which RNA polymerase II-blocking lesions are rapidly removed from the transcribed strand of active genes (PubMed:16246722, PubMed:20541997, PubMed:22483866, PubMed:26620705, PubMed:32355176, PubMed:34526721, PubMed:38316879, PubMed:38600235, PubMed:38600236). Plays a central role in the initiation of the TC-NER process: specifically recognizes and binds RNA polymerase II stalled at a lesion, and mediates recruitment of ERCC8/CSA, initiating DNA damage excision by TFIIH recruitment (PubMed:32355176, PubMed:34526721, PubMed:38600235, PubMed:38600236). Upon DNA-binding, it locally modifies DNA conformation by wrapping the DNA around itself, thereby modifying the interface between stalled RNA polymerase II and DNA (PubMed:15548521). Acts as a chromatin remodeler at DSBs; DNA-dependent ATPase-dependent activity is essential for this function (PubMed:16246722, PubMed:9565609). Plays an important role in regulating the choice of the DNA double-strand breaks (DSBs) repair pathway and G2/M checkpoint activation; DNA-dependent ATPase activity is essential for this function (PubMed:25820262). Regulates the DNA repair pathway choice by inhibiting non-homologous end joining (NHEJ), thereby promoting the homologous recombination (HR)-mediated repair of DSBs during the S/G2 phases of the cell cycle (PubMed:25820262). Mediates the activation of the ATM- and CHEK2-dependent DNA damage responses thus preventing premature entry of cells into mitosis following the induction of DNA DSBs (PubMed:25820262). Remodels chromatin by evicting histones from chromatin flanking DSBs, limiting RIF1 accumulation at DSBs thereby promoting BRCA1-mediated HR (PubMed:29203878). Required for stable recruitment of ELOA and CUL5 to DNA damage sites (PubMed:28292928). Also involved in UV-induced translocation of ERCC8 to the nuclear matrix (PubMed:26620705). Essential for neuronal differentiation and neuritogenesis; regulates transcription and chromatin remodeling activities required during neurogenesis (PubMed:24874740)","subcellular_location":"Nucleus; Chromosome","url":"https://www.uniprot.org/uniprotkb/Q03468/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ERCC6","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/ERCC6","total_profiled":1310},"omim":[{"mim_id":"619818","title":"ELONGATION FACTOR 1; ELOF1","url":"https://www.omim.org/entry/619818"},{"mim_id":"616946","title":"PREMATURE OVARIAN FAILURE 11; POF11","url":"https://www.omim.org/entry/616946"},{"mim_id":"615715","title":"BONE MARROW FAILURE SYNDROME 2; BMFS2","url":"https://www.omim.org/entry/615715"},{"mim_id":"615667","title":"ERCC EXCISION REPAIR 6-LIKE 2; ERCC6L2","url":"https://www.omim.org/entry/615667"},{"mim_id":"614848","title":"CENTROSOMAL PROTEIN, 164-KD; CEP164","url":"https://www.omim.org/entry/614848"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Nuclear bodies","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/ERCC6"},"hgnc":{"alias_symbol":["CSB","RAD26","ARMD5"],"prev_symbol":["CKN2"]},"alphafold":{"accession":"Q03468","domains":[{"cath_id":"3.40.50.10810","chopping":"493-749","consensus_level":"medium","plddt":86.1113,"start":493,"end":749},{"cath_id":"1.10.287","chopping":"101-201","consensus_level":"medium","plddt":85.5868,"start":101,"end":201},{"cath_id":"1.10.10","chopping":"1425-1489","consensus_level":"high","plddt":84.2246,"start":1425,"end":1489}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q03468","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q03468-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q03468-F1-predicted_aligned_error_v6.png","plddt_mean":60.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ERCC6","jax_strain_url":"https://www.jax.org/strain/search?query=ERCC6"},"sequence":{"accession":"Q03468","fasta_url":"https://rest.uniprot.org/uniprotkb/Q03468.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q03468/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q03468"}},"corpus_meta":[{"pmid":"33545094","id":"PMC_33545094","title":"Safety 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Mutation analysis showed the gene is not essential for cell viability but is specific for preferential repair of transcribed sequences.\",\n      \"method\": \"Gene cloning, complementation of CS-B cells, mutation analysis of CS-B patient\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — original cloning paper with complementation, mutation analysis, domain identification; foundational study replicated extensively\",\n      \"pmids\": [\"1339317\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"ERCC6 gene was cloned by complementation of the UV-sensitive CHO mutant UV61 (rodent complementation group 6), which harbors a deficiency in repair of UV-induced cyclobutane pyrimidine dimers but shows apparently normal repair of (6-4) photoproducts. The gene spans ~115 kb of genomic DNA.\",\n      \"method\": \"Genomic DNA transfection, complementation cloning, Southern blot analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — original cloning by functional complementation with rigorous controls\",\n      \"pmids\": [\"2172786\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"ERCC6 gene spans 82-90 kb, consists of at least 21 exons, contains seven distinct helicase signature domains encoded on separate exons, and produces two mRNA molecules of 5 and 7 kb via alternative polyadenylation.\",\n      \"method\": \"Genomic organization analysis, cDNA cloning, Northern blot\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct genomic and cDNA structural analysis\",\n      \"pmids\": [\"8382798\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Purified recombinant human CSB/ERCC6 protein is a DNA-stimulated ATPase but is not a helicase and does not disrupt the ternary transcription complex of stalled RNA polymerase II. CSB binds DNA and also physically interacts with XPA, TFIIH, and the p34 subunit of TFIIE.\",\n      \"method\": \"Baculovirus overexpression, protein purification, ATPase assay, helicase assay, RNA pol II stalling/dissociation assay, direct binding assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro biochemical reconstitution with purified recombinant protein, multiple assays\",\n      \"pmids\": [\"8999876\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"CSB/ERCC6 physically interacts with RNA polymerase II engaged in elongation ternary complexes containing DNA and nascent RNA, and this interaction requires ATP hydrolysis (the beta-gamma bond) to form a stable Pol II-CSB-DNA-RNA complex. CSA does not directly bind Pol II.\",\n      \"method\": \"Oligo(dC)-tailed DNA template biochemical assay, ATPase mutant analysis, binding assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with ternary complexes, mutagenesis of ATPase motif\",\n      \"pmids\": [\"9372911\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"CSB/ERCC6 restores transcription-coupled repair of UV-induced cyclobutane pyrimidine dimers (CPDs) in the transcribed strand of the actively transcribed DHFR gene when transfected into the TCR-deficient CHO cell line UV61, demonstrating that CSB has an independent role in TCR separate from general RNA Pol II transcription.\",\n      \"method\": \"Transfection complementation, strand-specific repair assay (gene-specific repair assay), CPD measurement\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional complementation with defined molecular readout in cell-based system\",\n      \"pmids\": [\"8811084\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Transcription-coupled repair of 8-oxoguanine requires CSB (as well as XPG and TFIIH). CS-B cells not only lack TCR of 8-oxoG but cannot remove 8-oxoG from a transcribed sequence despite proficient repair elsewhere; unrepaired 8-oxoG blocks RNA polymerase II transcription and leads to a mutation frequency of 30-40% vs normal 1-4%.\",\n      \"method\": \"Strand-specific repair assay, mutation frequency analysis, CS cell lines vs. normal human cells and XP cells\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-based genetic analysis with multiple CS and XP cell lines, quantitative readouts\",\n      \"pmids\": [\"10786832\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"CSB is a component of a nucleolar 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. CS-causing mutations in CSB (as well as XPB and XPD) disrupt the RNA pol I/TFIIH interaction within this complex.\",\n      \"method\": \"Immunoprecipitation, in vitro RNA pol I transcription assay, transfection complementation, immunofluorescence (nucleolar localization)\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro transcription reconstitution plus complementation and complex characterization\",\n      \"pmids\": [\"12419226\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"GFP-tagged CSB, expressed at physiological levels, is homogeneously dispersed in the nucleoplasm plus bright nuclear foci and nucleolar accumulation. FRAP studies showed GFP-CSB transiently interacts with the transcription elongation machinery as part of a high-molecular-weight complex; upon UV-induced transcription arrest, CSB binding to these complexes is prolonged, consistent with engagement in TC-NER.\",\n      \"method\": \"GFP tagging, live-cell imaging, FRAP (fluorescence recovery after photobleaching)\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct live-imaging with quantitative FRAP showing functional state-dependent dynamics\",\n      \"pmids\": [\"15226310\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"CSB actively wraps DNA around itself in an ATP-dependent manner: scanning force microscopy showed DNA contour length shortening upon CSB binding, consistent with DNA wrapping. Non-hydrolyzable ATP analogues increased the frequency of shorter DNA molecules, suggesting ATP binding promotes wrapping and ATP hydrolysis causes unwrapping. CSB likely binds DNA as a dimer.\",\n      \"method\": \"Scanning force microscopy, ATP and non-hydrolyzable ATP analogue comparison\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct structural/biophysical characterization with multiple conditions\",\n      \"pmids\": [\"15548521\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"CSB is a substrate of the CSA-containing E3 ubiquitin ligase complex: following UV irradiation, CSB is ubiquitinated and degraded by the proteasome in a CSA-dependent manner at a late stage of TC-NER. CSB degradation is required for post-TCR recovery of transcription.\",\n      \"method\": \"Ubiquitination assays, proteasome inhibition, CSA-deficient cells, RNA synthesis recovery assay\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (biochemical, genetic, functional) in a single study\",\n      \"pmids\": [\"16751180\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"UV-induced stable association of CSB with chromatin requires ATP hydrolysis. The N-terminal region of CSB negatively autoregulates chromatin association during normal growth, and ATP hydrolysis is required to overcome this inhibitory effect. Mutations causing Cockayne syndrome can underlie defects in this chromatin association mechanism.\",\n      \"method\": \"Chromatin fractionation, ATPase mutant analysis, deletion mapping of N-terminal region, UV treatment\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple mutants and conditions with direct chromatin fractionation readout\",\n      \"pmids\": [\"20122405\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Mutations in conserved ATPase motifs II, V, and VI of CSB differentially reduce ATPase activity, and dephosphorylation of CSB in vitro results in increased ATPase activity. UV irradiation leads to CSB dephosphorylation in cells, suggesting that phosphorylation status regulates CSB ATPase activity in vivo.\",\n      \"method\": \"Site-directed mutagenesis of helicase motifs, in vitro ATPase assay, phosphorylation analysis\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro biochemical assay with mutagenesis and biochemical regulation\",\n      \"pmids\": [\"12560492\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"UVSSA protein forms a complex with USP7, stabilizes ERCC6/CSB protein levels, and restores the hypophosphorylated form of RNA pol II after UV irradiation. Mutations in UVSSA cause UV-sensitive syndrome by destabilizing CSB.\",\n      \"method\": \"Microcell-mediated chromosome transfer (gene cloning), co-immunoprecipitation, complementation assay, western blot for CSB stability\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — gene cloning by functional approach, Co-IP, complementation, protein stability assays\",\n      \"pmids\": [\"22466612\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CSB displays strong affinity for DNA:RNA hybrids in vitro and acts as a sensor of ROS-induced R loops in transcribed regions. During transcription-coupled homologous recombination (TC-HR), CSB is recruited by R loops, then recruits RAD52 through an acidic domain of CSB, and the CSB-RAD52-RAD51 axis carries out a BRCA1/2-independent alternative HR pathway protecting the transcribed genome.\",\n      \"method\": \"In vitro DNA:RNA hybrid binding assay, ROS-induced R loop induction, laser microirradiation with fluorescent protein foci assay, epistasis with RAD52/BRCA1/BRCA2 knockdown\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vitro binding plus cell-based epistasis and imaging with multiple orthogonal approaches\",\n      \"pmids\": [\"30297739\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"ATM-dependent phosphorylation of CSB on S10 and CDK2-dependent phosphorylation on S158 are required for CSB's chromatin remodeling activity at DSBs. CSB interacts via its winged helix domain (WHD) with RIF1, and this interaction mediates CSB recruitment to DSBs in S phase. At DSBs, CSB remodels chromatin by evicting histones, which limits RIF1 and MAD2L2 accumulation but promotes BRCA1 accumulation, thereby regulating DSB repair pathway choice.\",\n      \"method\": \"Co-IP, phospho-specific mutant analysis, chromatin immunoprecipitation, histone eviction assay, DSB repair pathway choice analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods defining post-translational modifications and interaction domains with functional readouts\",\n      \"pmids\": [\"29203878\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CSB interacts with the BRCT domain of BRCA1 in a CDK-dependent manner (phosphorylation on S1276), peaking in late S/G2 phase. This interaction mediates CSB's association with the BRCA1-C complex (BRCA1, MRN, CtIP). CSB phosphorylation on S1276 promotes MRN- and CtIP-mediated DNA end resection for HR and restricts NHEJ, while being dispensable for histone eviction at DSBs.\",\n      \"method\": \"Co-IP, CDK inhibitor treatment, phospho-mutant analysis, DNA end resection assay, cell survival assay\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, phospho-mutant analysis, epistasis, multiple readouts\",\n      \"pmids\": [\"31501894\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CSB stimulates recruitment of XRCC1 (a BER-scaffolding protein) to 8-oxoG lesions in a transcription-dependent manner. OGG1 recruitment to 8-oxoG is independent of CSB. XRCC1 recruitment to BER-unrelated single-strand breaks does not require CSB, suggesting CSB specifically facilitates BER progression at transcribed genes by recruiting XRCC1 to BER-generated SSBs masked by stalled RNA polymerase II.\",\n      \"method\": \"Live-cell imaging with laser-assisted local induction of 8-oxoG, fluorescent protein recruitment kinetics, CSB knockdown and knockout cells\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — quantitative live imaging with multiple conditions and controls\",\n      \"pmids\": [\"29955842\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CSB loads the PAF1 complex (PAF1C) onto RNA polymerase II in promoter-proximal regions in response to DNA damage. PAF1C is dispensable for TCR-mediated repair but is essential for transcription recovery after UV irradiation by promoting RNAPII pause release in promoter-proximal regions and acting as a processivity factor for transcription elongation throughout genes.\",\n      \"method\": \"Co-IP, ChIP-seq, mass spectrometry, RNA recovery assays after UV, PAF1C knockdown, UV survival\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal approaches defining a new molecular pathway with clear functional readouts\",\n      \"pmids\": [\"33637760\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CSB and CSA are required for transcription-coupled DNA-protein crosslink (DPC) repair in actively transcribed genes. DPC formation arrests transcription, and CSB/CSA-deficient cells fail to efficiently restart transcription after DPC induction. Downstream TC-NER factors (XPA etc.) are dispensable, indicating a non-canonical TC-NER mechanism for DPCs. TC-DPC repair is mediated by the ubiquitin ligase CRL4CSA and the proteasome.\",\n      \"method\": \"DPC sequencing (genome-wide DPC mapping), genetic screens, transcription restart assays, cell survival assays, epistasis with NER factors\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genome-wide mapping plus genetic and biochemical epistasis in two independent concurrent studies\",\n      \"pmids\": [\"38600235\", \"38600236\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"CSB expression is directly regulated by HIF-1; CSB mutant cells fail to properly activate the HIF-1 pathway under hypoxia. CSB redistributes p300 between HIF-1 and p53, functioning in a feedback loop that modulates p53 biological functions during hypoxic response.\",\n      \"method\": \"Reporter assays, ChIP, co-immunoprecipitation, CSB-deficient cell analysis, HIF-1 pathway activation assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple methods but single lab\",\n      \"pmids\": [\"18784753\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"CSB and CSA associate in a unique complex with p53 and Mdm2 (a Cullin Ring Ubiquitin Ligase complex), and this interaction greatly stimulates Mdm2-dependent ubiquitination of p53. Absence of CSB leads to elevated and persistent p53 levels due to insufficient ubiquitination.\",\n      \"method\": \"Co-IP, tandem affinity purification, mass spectrometry, ubiquitination assays, CS patient cell analysis\",\n      \"journal\": \"Cell cycle\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — TAP/MS plus Co-IP and functional ubiquitination assays, single lab\",\n      \"pmids\": [\"22032989\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"CSB directly interacts with SNM1A (a 5'-3' exonuclease), modulates SNM1A's exonuclease activity on oligonucleotide substrates in vitro, and co-exists with SNM1A in a common complex in human cell extracts. Both proteins are recruited to trioxsalen-induced interstrand crosslink (ICL) damage in transcription-dependent manner; SNM1A recruitment is reduced in CSB-deficient cells. CSB-deficient neural cells show increased sensitivity to crosslinking agents and delayed ICL processing.\",\n      \"method\": \"Yeast two-hybrid, purified recombinant protein interaction, in vitro exonuclease assay, Co-IP from cell extracts, laser microirradiation + fluorescence microscopy, comet assay, γ-H2AX foci\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro reconstitution plus cell-based imaging and functional assays, multiple orthogonal methods\",\n      \"pmids\": [\"25505141\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"VCP/p97 segregase mediates UV-induced ubiquitin-mediated CSB degradation. VCP/p97 interacts with both native and ubiquitin-conjugated forms of CSB, and VCP/p97 cofactors UFD1 and UBXD7 are required for CSB degradation. VCP/p97 associates with the CSA-DDB1-Cul4A E3 ligase complex. Inhibition of VCP/p97 causes accumulation of ubiquitinated CSB in chromatin and unexpectedly enhances recovery of RNA synthesis following UV.\",\n      \"method\": \"Co-IP, VCP/p97 inhibitors, siRNA depletion, localized UV irradiation with foci analysis, RNA synthesis recovery assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP and multiple genetic/pharmacological perturbations, single lab\",\n      \"pmids\": [\"26826127\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"NAP1L1 histone chaperone interacts with CSB and enhances CSB-mediated nucleosome remodeling. Single-molecule analysis showed CSB remodels nucleosomes via three phases (activation, translocation, pausing), and NAP1L1 accelerates both activation and translocation phases and decreases pausing probability, thereby increasing processivity.\",\n      \"method\": \"Single-molecule FRET/fluorescence microscopy, ATPase assay, in vitro nucleosome remodeling assay\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — single-molecule real-time analysis with reconstituted nucleosomes\",\n      \"pmids\": [\"28369616\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"A conserved 'leucine latch' motif at the N terminus of Rhp26 (S. pombe ortholog of CSB/ERCC6) mediates autoinhibition of ATPase and chromatin-remodeling activities via interaction with the core ATPase domain. The C terminus counteracts this autoinhibition; both N- and C-terminal regions are needed for proper DNA repair function in vivo.\",\n      \"method\": \"Mutagenesis, in vitro ATPase assay, nucleosome remodeling assay, in vivo DNA repair assay, protein interaction studies\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution, mutagenesis, and in vivo complementation; conserved leucine latch also present in human CSB\",\n      \"pmids\": [\"25512493\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"ROS-induced DNA damage at telomeres triggers R-loop accumulation in a TERRA- and TRF2-dependent manner. CSB and RAD52 are recruited to telomeric R-loops; RAD52 is recruited through interactions with both CSB and DNA:RNA hybrids. Both CSB and RAD52 are required for efficient repair of ROS-induced telomeric DSBs through a CSB-RAD52-POLD3-mediated break-induced replication pathway.\",\n      \"method\": \"Live-cell imaging, ChIP, immunoprecipitation, knockdown of CSB/RAD52/POLD3, R-loop detection (S9.6 antibody), comet assay\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods with clear epistasis\",\n      \"pmids\": [\"31777915\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CSB promotes recruitment of HR repair proteins (MRN, BRCA1, BLM, RPA32) and POLD3 to ALT telomeres via its ATPase activity (controlled by ATM- and CDK2-dependent phosphorylation). Loss of CSB stimulates telomeric recruitment of MUS81 and SLX4 (MUS-SLX endonuclease complex), suggesting CSB restricts MUS-SLX-mediated processing of stalled forks at ALT telomeres.\",\n      \"method\": \"Fluorescence imaging with tagged proteins, phospho-mutant analysis, epistasis with SMARCAL1 depletion, ATM/CDK2 inhibitor treatment\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — cell-based imaging with multiple conditions, single lab\",\n      \"pmids\": [\"31974116\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CSB regulates PARP1- and PARP2-mediated single-strand break repair (SSBR) at actively transcribed DNA regions. PARP1 and PARP2 promote CSB recruitment to oxidatively-damaged DNA; CSB in turn promotes XRCC1 and HPF1 recruitment and histone PARylation. CSB's function in SSBR is bypassed when transcription is inhibited, showing CSB-mediated SSBR occurs primarily at actively transcribed regions.\",\n      \"method\": \"Chromatin co-fractionation, alkaline comet assay, transcription inhibition, siRNA depletion, immunofluorescence\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple biochemical and cell-based approaches, single lab\",\n      \"pmids\": [\"37326017\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"CSB gene contains a domesticated PiggyBac-like transposon (PGBD3) in intron 5 that functions as an alternative 3' terminal exon, producing a CSB-PGBD3 fusion protein by alternative splicing of CSB exons 1–5 to the PGBD3 transposase. This fusion protein is as abundant as CSB protein in various human cell lines and continues to be expressed in CS cells with mutations beyond exon 5.\",\n      \"method\": \"RT-PCR, western blot, expression analysis in multiple cell lines, evolutionary conservation analysis\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple methods documenting expression and evolutionary conservation\",\n      \"pmids\": [\"18369450\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"CSB mutant (CS patient) cells, but not UVSS cells, show depletion of mitochondrial DNA polymerase-γ catalytic subunit (POLG1) due to CSA/CSB-dependent accumulation of HTRA3 serine protease. Inhibition of serine proteases restored POLG1 levels in CS fibroblasts. CS cells showed greater nitroso-redox imbalance and altered mitochondrial oxidative phosphorylation compared to UVSS cells.\",\n      \"method\": \"Western blot, siRNA depletion of CSB, serine protease inhibitors, ROS scavengers, mitochondrial OXPHOS measurement\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple pharmacological and genetic tools with biochemical readouts, single lab\",\n      \"pmids\": [\"26038566\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"CSB directly interacts with CTCF in vitro, and oxidative stress enhances the CSB-CTCF interaction in cells. CSB facilitates CTCF-DNA interactions in vitro and regulates CTCF-chromatin interactions in oxidatively stressed cells. Oxidative stress alters CSB's genomic occupancy and increases CSB occupancy at promoters, with CTCF regulating sites of CSB occupancy.\",\n      \"method\": \"ChIP-seq, in vitro protein interaction assay, co-IP from cells, oxidative stress treatment\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro direct interaction plus ChIP-seq and co-IP, single lab\",\n      \"pmids\": [\"26578602\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Cryo-EM structures of yeast Pol II-Rad26 complexes (ortholog of CSB) show that Rad26 uses a common mechanism to recognize stalled Pol II, with additional interactions when Pol II is arrested at a DNA lesion. Elf1 (ortholog of human ELOF1) induces further interactions between Rad26 and lesion-arrested Pol II. Biochemical and genetic data show that interplay between Elf1 and Rad26 is important for TC-NER initiation.\",\n      \"method\": \"Cryo-EM structure determination, biochemical assays, genetic analysis in yeast\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structures with biochemical and genetic validation\",\n      \"pmids\": [\"38194460\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"RAD26, the S. cerevisiae ortholog of ERCC6/CSB, is required for preferential TCR of UV-induced cyclobutane pyrimidine dimers from the transcribed strand of the active RBP2 gene. Disruption of RAD26 does not cause UV sensitivity (unlike human CSB mutations), indicating TCR in lower eukaryotes is not critical for cell survival.\",\n      \"method\": \"Gene cloning, RAD26 disruption mutant, strand-specific repair assay, UV/cisplatin/X-ray sensitivity testing\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic complementation and strand-specific repair assay in yeast ortholog\",\n      \"pmids\": [\"7957102\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Purified yeast Rad26 protein (ortholog of human CSB) is a DNA-dependent ATPase that is much more active and strictly DNA-dependent compared to the E. coli Mfd protein, suggesting Rad26 may displace stalled RNA pol II or recruit repair components at DNA lesions.\",\n      \"method\": \"Yeast protein purification, in vitro ATPase assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — purified protein biochemical reconstitution\",\n      \"pmids\": [\"8702468\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Yeast Def1 forms a complex with Rad26 (CSB ortholog) in chromatin. In response to DNA damage, Rad26 promotes TCR while Def1 is required for ubiquitination and degradation of stalled RNA polymerase II (RNAPII) when lesions cannot be rapidly removed, providing a coordinated rescue mechanism for Pol II stalled at DNA lesions.\",\n      \"method\": \"Protein complex identification, genetic analysis, RNAPII ubiquitination assay, chromatin fractionation\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — protein complex identification plus genetic and biochemical characterization of RNAPII degradation\",\n      \"pmids\": [\"11859374\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"CSB plays a general role in chromatin maintenance and remodeling: genes regulated by CSB overlap significantly with genes affected by HDAC inhibitors, DNA methylation inhibitors, PARP inhibitors, and RNA pol II elongation inhibitors. CSB-null cells are sensitive to HDAC and PARP inhibitors, indicating CSB has broad chromatin maintenance functions beyond TC-NER.\",\n      \"method\": \"Expression microarrays, comparative L2L analysis, drug sensitivity assays (HDAC and PARP inhibitors)\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — transcriptomic plus pharmacological sensitivity, indirect mechanistic evidence\",\n      \"pmids\": [\"16772382\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ERCC6/CSB is an ATP-dependent SWI2/SNF2-family chromatin remodeler and DNA-stimulated ATPase that initiates transcription-coupled nucleotide excision repair (TC-NER) by recognizing RNA polymerase II stalled at DNA lesions—requiring ATP hydrolysis for stable chromatin association (regulated by N-terminal autoinhibition, ATM/CDK2-dependent phosphorylation, and CSA-mediated ubiquitin-proteasomal degradation after repair)—and additionally functions in RNA pol I transcription, base excision repair at transcribed regions (recruiting XRCC1 via PARP1/2), transcription-coupled DPC repair, BRCA1/2-independent homologous recombination at R-loops, DSB repair pathway choice (chromatin remodeling to promote HR over NHEJ), and telomere maintenance in ALT cells, while also loading PAF1C onto RNAPII to restore transcription elongation genome-wide after genotoxic stress.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"ERCC6/CSB is an ATP-dependent SWI2/SNF2-family chromatin remodeler that serves as a master coordinator of transcription-coupled DNA repair and transcription recovery at sites of RNA polymerase stalling. CSB is a DNA-stimulated ATPase (not a helicase) that wraps DNA in an ATP-dependent manner, physically associates with elongating RNA polymerase II through ATP hydrolysis, and is recruited to stalled polymerases at UV-induced lesions, oxidative damage (8-oxoguanine), interstrand crosslinks, and DNA-protein crosslinks to initiate transcription-coupled nucleotide excision repair and transcription-coupled base excision repair [PMID:1339317, PMID:8999876, PMID:9372911, PMID:10786832, PMID:38600235, PMID:29955842]. Its chromatin association is autoinhibited by an N-terminal region and activated by ATP hydrolysis and phosphorylation (ATM on S10, CDK2 on S158, CDK on S1276), enabling functions beyond TC-NER including histone eviction at DSBs to promote HR over NHEJ, BRCA1/2-independent homologous recombination at R-loops via RAD52 recruitment, telomere maintenance in ALT cells, RNA polymerase I-dependent rRNA synthesis, and PAF1C loading onto RNAPII for post-damage transcription restart [PMID:20122405, PMID:29203878, PMID:30297739, PMID:31501894, PMID:12419226, PMID:33637760]. CSB is regulated by CSA-DDB1-CUL4A E3 ligase-mediated ubiquitination and VCP/p97-dependent proteasomal degradation after repair completion, and is stabilized by the UVSSA-USP7 complex; loss-of-function mutations cause Cockayne syndrome, a multisystem disorder of defective transcription-coupled repair [PMID:16751180, PMID:22466612, PMID:26826127].\",\n  \"teleology\": [\n    {\n      \"year\": 1990,\n      \"claim\": \"Cloning of ERCC6 by functional complementation of the UV-sensitive CHO mutant UV61 established that a single gene corrects a specific deficiency in cyclobutane pyrimidine dimer repair, linking ERCC6 to a distinct DNA repair pathway.\",\n      \"evidence\": \"Genomic DNA transfection and complementation cloning in CHO UV61 cells\",\n      \"pmids\": [\"2172786\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No protein product characterized\", \"Mechanism of repair deficiency unknown\", \"Human disease connection not yet established\"]\n    },\n    {\n      \"year\": 1992,\n      \"claim\": \"Full-length cloning and characterization of the ERCC6/CSB protein revealed SWI2/SNF2-family helicase motifs and demonstrated that CSB is specifically required for transcription-coupled NER — the preferential repair of lesions on the transcribed strand of active genes — establishing the molecular identity of the Cockayne syndrome group B gene.\",\n      \"evidence\": \"cDNA cloning, complementation of CS-B patient cells, domain analysis, mutation identification\",\n      \"pmids\": [\"1339317\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Biochemical activity of the protein unknown\", \"Mechanism of coupling to transcription unclear\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Identification of RAD26 as the yeast ortholog of ERCC6 confirmed that transcription-coupled repair is an evolutionarily conserved pathway, though dispensability for UV survival in yeast suggested additional functions in mammals.\",\n      \"evidence\": \"Gene disruption and strand-specific repair assay in S. cerevisiae\",\n      \"pmids\": [\"7957102\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why yeast tolerates loss of TCR while human cells do not\", \"Direct protein activity of Rad26 not yet measured\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Biochemical reconstitution resolved the paradox of CSB's helicase motifs: CSB is a DNA-stimulated ATPase but not a helicase, and it physically interacts with elongating RNA polymerase II in an ATP-hydrolysis-dependent manner, establishing the mechanism of TC-NER initiation.\",\n      \"evidence\": \"Purified recombinant CSB — ATPase, helicase, and Pol II ternary complex binding assays with ATPase mutants\",\n      \"pmids\": [\"8999876\", \"9372911\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CSB remodels chromatin directly\", \"How ATP hydrolysis stabilizes the Pol II interaction structurally\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Demonstration that CSB is required for transcription-coupled repair of 8-oxoguanine expanded CSB's substrate repertoire beyond UV-induced CPDs to oxidative base lesions, explaining why CS patients exhibit features beyond UV sensitivity.\",\n      \"evidence\": \"Strand-specific repair and mutation frequency assays in CS-B cell lines\",\n      \"pmids\": [\"10786832\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CSB recruits BER factors or only initiates TCR at oxidative lesions\", \"Mechanism of Pol II stalling at 8-oxoG\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Discovery that CSB resides in a nucleolar complex with RNA Pol I, TFIIH, and XPG and promotes rRNA synthesis revealed that CSB functions extend beyond DNA repair to active transcription by RNA polymerase I.\",\n      \"evidence\": \"Immunoprecipitation, in vitro RNA Pol I transcription, complementation in CSB-deficient cells\",\n      \"pmids\": [\"12419226\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CSB remodels rDNA chromatin directly\", \"Contribution to Cockayne syndrome neurodegeneration\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Biophysical studies established that CSB wraps DNA around itself in an ATP-dependent manner and transiently associates with the transcription elongation machinery, with UV damage prolonging this association — defining CSB as a bona fide chromatin remodeler acting at sites of transcription arrest.\",\n      \"evidence\": \"Scanning force microscopy of DNA-CSB complexes and live-cell FRAP of GFP-CSB\",\n      \"pmids\": [\"15548521\", \"15226310\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Nucleosome substrate remodeling not yet directly shown\", \"No structural model of CSB on chromatin\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Identification of CSB as a substrate of the CSA-containing CRL4 E3 ubiquitin ligase resolved how TC-NER is terminated: UV-induced ubiquitination and proteasomal degradation of CSB is required for post-repair transcription recovery.\",\n      \"evidence\": \"Ubiquitination assays, proteasome inhibition, CSA-deficient cells, RNA synthesis recovery\",\n      \"pmids\": [\"16751180\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the ubiquitin chain type on CSB\", \"How CSB degradation timing is controlled\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Mapping of an N-terminal autoinhibitory domain that restricts CSB's chromatin association during normal growth, overcome by ATP hydrolysis upon UV damage, provided a regulatory mechanism ensuring CSB activation is lesion-dependent.\",\n      \"evidence\": \"Chromatin fractionation with ATPase and N-terminal deletion mutants\",\n      \"pmids\": [\"20122405\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of autoinhibition in human CSB\", \"Whether post-translational modifications regulate autoinhibition\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Discovery that UVSSA-USP7 stabilizes CSB protein levels explained how CSB abundance is maintained during repair and identified UVSSA mutations as the cause of UV-sensitive syndrome, distinguishing it from Cockayne syndrome.\",\n      \"evidence\": \"Complementation cloning, co-immunoprecipitation, CSB stability western blots\",\n      \"pmids\": [\"22466612\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise ubiquitin editing mechanism on CSB by USP7\", \"Whether UVSSA modulates CSB activity beyond stabilization\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Characterization of a conserved 'leucine latch' motif in the CSB ortholog Rhp26 defined the structural basis of N-terminal autoinhibition of ATPase and remodeling activity, with the C-terminus serving as a counterbalance — a mechanism conserved to human CSB.\",\n      \"evidence\": \"Mutagenesis, in vitro ATPase and nucleosome remodeling, in vivo complementation in S. pombe\",\n      \"pmids\": [\"25512493\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct demonstration of leucine-latch mechanism in human CSB\", \"Allosteric coupling mechanism between termini and ATPase domain\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Three contemporaneous studies expanded CSB's functions to DSB repair pathway choice and R-loop-dependent homologous recombination: ATM/CDK2-dependent phosphorylation drives CSB's chromatin remodeling at DSBs to evict histones and promote HR over NHEJ, while CSB senses R-loops and recruits RAD52 for BRCA1/2-independent HR, and NAP1L1 enhances CSB nucleosome remodeling processivity.\",\n      \"evidence\": \"Phospho-mutant analysis with histone eviction assays; in vitro DNA:RNA hybrid binding with epistasis; single-molecule FRET nucleosome remodeling\",\n      \"pmids\": [\"29203878\", \"30297739\", \"28369616\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CSB-RAD52 HR operates at non-telomeric loci genome-wide\", \"Structural basis of CSB recognition of R-loops versus naked DNA\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Live-cell imaging demonstrated that CSB specifically recruits XRCC1 to 8-oxoG lesions in a transcription-dependent manner, establishing CSB as a bridge between stalled Pol II and downstream BER completion at transcribed genes.\",\n      \"evidence\": \"Laser-induced 8-oxoG with fluorescent XRCC1/OGG1 recruitment kinetics in CSB-KO cells\",\n      \"pmids\": [\"29955842\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CSB physically contacts XRCC1 or acts indirectly through chromatin remodeling\", \"Full BER intermediate processing at stalled Pol II sites\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"CDK-dependent phosphorylation of CSB at S1276 mediates interaction with BRCA1-BRCT domain, promoting MRN/CtIP-mediated end resection for HR at DSBs — separating CSB's resection-promoting function from its histone-eviction activity.\",\n      \"evidence\": \"Phospho-mutant co-IP, CDK inhibitor treatment, end resection assays\",\n      \"pmids\": [\"31501894\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether S1276 phosphorylation and S10/S158 phosphorylation are coordinated temporally\", \"Structural basis of CSB-BRCA1 BRCT interaction\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"CSB was shown to operate at telomeres in ALT cells, where it recruits RAD52 and POLD3 for break-induced replication at R-loop-containing telomeric DSBs, extending CSB's R-loop repair function to telomere maintenance.\",\n      \"evidence\": \"ChIP, live-cell imaging, epistasis with CSB/RAD52/POLD3 knockdown, S9.6 R-loop detection at telomeres\",\n      \"pmids\": [\"31777915\", \"31974116\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CSB is required for ALT telomere maintenance in vivo (animal model)\", \"Mechanism distinguishing telomeric from genomic R-loop repair\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Discovery that CSB loads PAF1C onto RNAPII at promoter-proximal regions after DNA damage resolved how transcription restarts genome-wide after genotoxic stress — PAF1C is dispensable for repair itself but essential for elongation recovery.\",\n      \"evidence\": \"Co-IP, ChIP-seq, mass spectrometry, RNA recovery assays, PAF1C knockdown\",\n      \"pmids\": [\"33637760\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CSB-PAF1C loading is specific to UV or general across damage types\", \"Structural basis of CSB-PAF1C-RNAPII assembly\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"CSB was placed downstream of PARP1/2 signaling at oxidatively damaged transcribed DNA, where it promotes XRCC1, HPF1 recruitment and histone PARylation for single-strand break repair — a function bypassed when transcription is inhibited.\",\n      \"evidence\": \"Chromatin co-fractionation, alkaline comet assay, transcription inhibition, siRNA in human cells\",\n      \"pmids\": [\"37326017\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct physical interaction between CSB and PARP1/2 not demonstrated with purified proteins\", \"Whether HPF1 recruitment is CSB-dependent or PARP-dependent\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Cryo-EM structures of yeast Pol II-Rad26 complexes and functional studies of transcription-coupled DPC repair established the structural basis of CSB/Rad26 recognition of stalled Pol II, and expanded CSB's repair substrates to DNA-protein crosslinks via a non-canonical TC-NER mechanism requiring CRL4^CSA and the proteasome.\",\n      \"evidence\": \"Cryo-EM structures with biochemical/genetic validation (yeast); DPC-seq, genetic epistasis, transcription restart assays (human)\",\n      \"pmids\": [\"38194460\", \"38600235\", \"38600236\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No cryo-EM structure of human CSB-Pol II complex\", \"DPC substrate specificity and size limits for TC-DPC repair unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A high-resolution structure of human CSB engaged with Pol II on nucleosomal DNA, the precise allosteric mechanism linking autoinhibition relief to lesion-dependent activation, and how CSB's multiple repair and transcription functions are coordinated in time and space in vivo remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No human CSB-Pol II cryo-EM structure\", \"In vivo single-molecule dynamics of CSB at different damage types not resolved\", \"How CSB chooses between TC-NER, TC-BER, TC-HR, and TC-DPC repair pathways at a given lesion\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [3, 4, 9, 12, 34]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [3, 9, 14]},\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [14]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [24, 25]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005654\", \"supporting_discovery_ids\": [8, 11]},\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [7, 8]},\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [11, 15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [0, 1, 5, 6, 17, 19, 22, 28, 32, 33]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [7, 18]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [15, 24, 25, 36]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [7, 18]}\n    ],\n    \"complexes\": [\n      \"CSA-DDB1-CUL4A E3 ligase complex\",\n      \"RNA Pol I/TFIIH/XPG nucleolar complex\",\n      \"UVSSA-USP7 complex\"\n    ],\n    \"partners\": [\n      \"ERCC8\",\n      \"UVSSA\",\n      \"RAD52\",\n      \"BRCA1\",\n      \"XRCC1\",\n      \"XPA\",\n      \"RIF1\",\n      \"SNM1A\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}