{"gene":"LEO1","run_date":"2026-06-10T02:59:49","timeline":{"discoveries":[{"year":2002,"finding":"Leo1 (along with Ctr9 and Rtf1) is a component of the Paf1/RNA Polymerase II complex in S. cerevisiae, distinct from the Srb-mediator form of Pol II holoenzyme. Deletion of LEO1 suppresses many paf1Δ phenotypes (e.g., restores CLN1 expression), indicating Leo1 participates in the same functional complex as Paf1.","method":"Tandem affinity purification, mass spectrometry, genetic epistasis (double-mutant analysis)","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — biochemical purification with mass spectrometry plus genetic epistasis, foundational study replicated by subsequent work","pmids":["11884586"],"is_preprint":false},{"year":2010,"finding":"The Leo1 subunit of the yeast Paf1 complex directly binds RNA in vitro. In vivo RNA-IP showed that Leo1, but not Rtf1, is necessary for Paf1C to associate with RNA. Cells lacking Leo1 show reduced Paf1C recruitment to transcribed chromatin and decreased levels of histone H3 and H3K4me3, suggesting Leo1-RNA interaction stabilizes complex localization at actively transcribed regions to influence chromatin structure.","method":"In vitro RNA-binding assay with purified protein, RNA immunoprecipitation (RNA-IP) in vivo, ChIP","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — in vitro reconstitution of RNA binding combined with in vivo RNA-IP and ChIP, multiple orthogonal methods in a single study","pmids":["20732871"],"is_preprint":false},{"year":2015,"finding":"In fission yeast, the Leo1-Paf1 subcomplex of Paf1C is required to prevent heterochromatin spreading into euchromatin. Deletion of Leo1 decreases nucleosome turnover at heterochromatin boundary regions, leading to stabilization of heterochromatin (increased H3K9me2), in an RNAi-independent manner.","method":"Genome-wide ChIP-exo for H3K9me2, random mutant screen, nucleosome turnover assays","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 2 / Moderate — high-resolution genome-wide ChIP-exo combined with nucleosome turnover assays and genetic loss-of-function, multiple orthogonal methods","pmids":["26518661"],"is_preprint":false},{"year":2010,"finding":"In zebrafish, Leo1 is a nuclear protein; a mutant Leo1 lacking the nuclear localization signal is redistributed to the cytoplasm and causes defects in cardiomyocyte differentiation at the atrioventricular boundary and loss of neural crest cell populations, establishing a functional requirement for nuclear Leo1 in vertebrate development.","method":"Genetic screen, identification of loss-of-function mutant, subcellular localization (nuclear vs. cytoplasmic distribution), phenotypic analysis of cardiac and neural crest markers","journal":"Developmental biology","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — genetic loss-of-function with defined cellular phenotypes and direct localization experiment, single lab","pmids":["20178782"],"is_preprint":false},{"year":2014,"finding":"In AML cells, PRL-3 (an oncogenic phosphatase) upregulates LEO1 expression by increasing JMJD2C histone demethylase occupancy on the LEO1 promoter, thereby reducing H3K9me3 repressive marks. LEO1 in turn stabilizes the PAF complex and maintains expression of SOX2 and SOX4 oncogenes; loss of LEO1 destabilizes the PAF complex and reverses PRL-3 oncogenic phenotypes.","method":"SILAC-based quantitative proteomics, ChIP for histone marks and JMJD2C, LEO1 knockdown/overexpression, PAF complex co-immunoprecipitation","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — SILAC proteomics plus ChIP plus Co-IP and functional KD, multiple methods but single lab","pmids":["24686170"],"is_preprint":false},{"year":2017,"finding":"In Drosophila, the PAF1 complex component Leo1 physically interacts with Myc and helps recruit Myc to target gene promoters. Because PAF1C is associated with active genes, Leo1 contributes to Myc targeting to open chromatin/active promoters.","method":"Co-immunoprecipitation / physical interaction assays, ChIP for Myc binding at target promoters with and without Leo1","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — physical interaction demonstrated and ChIP showing reduced Myc recruitment, single lab with two orthogonal methods","pmids":["29078288"],"is_preprint":false},{"year":2023,"finding":"CDK12 phosphorylates LEO1 (identified by chemical genetic and phosphoproteomic screening). Acute depletion of LEO1 or substitution of its CDK12 phosphorylation sites with alanine attenuates PAF1C association with elongating RNA Pol II and impairs processive transcription elongation. LEO1 is also dephosphorylated by the Integrator-PP2A complex (INTAC); depletion of INTAC promotes PAF1C–Pol II association, revealing antagonistic regulation of LEO1 phosphorylation by CDK12 and INTAC.","method":"Chemical genetic CDK12 inhibition, phosphoproteomic mass spectrometry, alanine-substitution mutagenesis, co-immunoprecipitation of PAF1C with Pol II, nascent transcription elongation assays","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — phosphoproteomic substrate identification validated by in-cell phospho-mutagenesis, Co-IP, and functional elongation assays; multiple orthogonal methods in one rigorous study","pmids":["37205756"],"is_preprint":false},{"year":2021,"finding":"LEO1 directly interacts with Cockayne syndrome protein B (CSB/ERCC6) in vitro and co-exists in a common complex in human cells. Both proteins are recruited to sites of DNA damage. Following UVC or cisplatin treatment, LEO1 and CSB show a transcription-dependent, coordinated association with chromatin. LEO1 knockdown reduces CSB chromatin recruitment, increases UV/cisplatin sensitivity, impairs RNA synthesis recovery, and slows cyclobutane pyrimidine dimer excision; CSB absence similarly reduces LEO1 chromatin recruitment, indicating reciprocal functional dependence in transcription-coupled DNA repair.","method":"Yeast two-hybrid screening, in vitro direct interaction with purified recombinant proteins, co-immunoprecipitation in human cells, fluorescent recruitment to laser-induced DNA damage sites, cell fractionation (chromatin association), LEO1 knockdown/knockout functional assays (RNA synthesis recovery, CPD excision, clonogenic survival)","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (Y2H, in vitro reconstitution, Co-IP, live-cell imaging, functional KD/KO assays) in a single rigorous study","pmids":["34096589"],"is_preprint":false}],"current_model":"LEO1 is a core subunit of the RNA Polymerase II-associated PAF1 complex that stabilizes PAF1C on actively transcribed chromatin by directly binding nascent RNA, undergoes CDK12-mediated phosphorylation (opposed by the Integrator-PP2A complex) to regulate PAF1C association with elongating Pol II and processive transcription elongation, prevents heterochromatin spreading by promoting nucleosome turnover, helps recruit transcription factors such as Myc to active promoters, and partners with the DNA repair factor CSB in a reciprocal, transcription-dependent manner to facilitate transcription-coupled nucleotide excision repair."},"narrative":{"mechanistic_narrative":"LEO1 is a core subunit of the RNA Polymerase II-associated PAF1 complex (PAF1C) that couples transcription elongation to chromatin structure and genome maintenance [PMID:11884586, PMID:20732871]. It anchors PAF1C on actively transcribed chromatin through direct binding to nascent RNA, and loss of LEO1 reduces PAF1C recruitment to transcribed regions along with histone H3 occupancy and H3K4me3 [PMID:20732871]. LEO1 association with elongating Pol II is dynamically controlled by phosphorylation: CDK12 phosphorylates LEO1 to promote processive elongation, while the Integrator-PP2A (INTAC) complex dephosphorylates it, establishing antagonistic regulation of PAF1C-Pol II engagement [PMID:37205756]. Through nucleosome turnover at heterochromatin boundaries, LEO1 prevents heterochromatin spreading into euchromatin independently of RNAi [PMID:26518661]. Beyond elongation, LEO1 helps recruit sequence-specific factors such as Myc to active promoters [PMID:29078288] and partners reciprocally with the Cockayne syndrome protein CSB/ERCC6 in a transcription-dependent manner to facilitate transcription-coupled nucleotide excision repair [PMID:34096589]. Nuclear LEO1 is required for vertebrate development, including cardiomyocyte differentiation and neural crest maintenance [PMID:20178782].","teleology":[{"year":2002,"claim":"Establishing that Leo1 is a bona fide member of the Paf1/Pol II complex defined the protein's primary functional context as transcription rather than the Srb-mediator holoenzyme.","evidence":"Tandem affinity purification with mass spectrometry and genetic epistasis in S. cerevisiae","pmids":["11884586"],"confidence":"High","gaps":["Molecular role of Leo1 within the complex unresolved","No mechanism for how Leo1 contributes to Pol II function"]},{"year":2010,"claim":"Identifying Leo1 as the RNA-binding subunit explained how PAF1C is retained on actively transcribed chromatin and linked this to histone modification.","evidence":"In vitro RNA-binding with purified protein, in vivo RNA-IP, and ChIP in yeast","pmids":["20732871"],"confidence":"High","gaps":["RNA sequence/structure specificity not defined","Structural basis of RNA contact unknown","Causal link between RNA binding and H3K4me3 indirect"]},{"year":2010,"claim":"Demonstrating that nuclear localization of Leo1 is required for vertebrate development extended its role from yeast transcription to organismal differentiation programs.","evidence":"Genetic loss-of-function mutant, NLS-deletion mislocalization, and cardiac/neural crest phenotyping in zebrafish","pmids":["20178782"],"confidence":"Medium","gaps":["Molecular targets driving cardiac/neural crest defects not identified","Whether phenotypes reflect PAF1C-dependent transcription unclear"]},{"year":2014,"claim":"Placing LEO1 downstream of an oncogenic phosphatase and as a stabilizer of the PAF complex connected its transcriptional role to maintenance of oncogene expression in leukemia.","evidence":"SILAC proteomics, ChIP for histone marks/JMJD2C, and PAF complex Co-IP with LEO1 knockdown in AML cells","pmids":["24686170"],"confidence":"Medium","gaps":["Direct vs indirect control of SOX2/SOX4 not separated","Single-lab finding","Generality across cancer types untested"]},{"year":2017,"claim":"Showing Leo1 physically interacts with Myc and aids its promoter recruitment revealed a mechanism by which PAF1C directs a transcription factor to active chromatin.","evidence":"Co-immunoprecipitation and Myc ChIP at target promoters with/without Leo1 in Drosophila","pmids":["29078288"],"confidence":"Medium","gaps":["Direct vs PAF1C-bridged interaction not resolved","Mapped interaction interface unknown","Single-lab data"]},{"year":2021,"claim":"Identifying a reciprocal LEO1-CSB partnership established a direct role for LEO1 in transcription-coupled nucleotide excision repair beyond canonical elongation.","evidence":"Y2H, in vitro reconstitution, Co-IP in human cells, laser-induced damage recruitment, and KD/KO functional repair assays","pmids":["34096589"],"confidence":"High","gaps":["Structural interface of LEO1-CSB undefined","How PAF1C function intersects with NER machinery mechanistically unclear"]},{"year":2023,"claim":"Defining LEO1 as a CDK12 substrate antagonized by INTAC explained how PAF1C-Pol II association and processive elongation are dynamically tuned by phosphorylation.","evidence":"Chemical genetic CDK12 inhibition, phosphoproteomics, alanine phospho-mutants, PAF1C-Pol II Co-IP, and nascent elongation assays in human cells","pmids":["37205756"],"confidence":"High","gaps":["Specific phospho-sites' structural effect on PAF1C binding unresolved","Interplay between phosphoregulation and RNA-binding-mediated retention unknown"]},{"year":null,"claim":"How LEO1's RNA-binding, phosphoregulation, transcription-factor recruitment, and DNA-repair functions are integrated within a single mechanistic framework remains open.","evidence":"","pmids":[],"confidence":"High","gaps":["No structural model of LEO1 within PAF1C on Pol II","RNA-binding specificity uncharacterized","Coordination of elongation and TC-NER roles unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[1]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[5]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[3]},{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[1,7]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,1,6]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[1,2]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[7]}],"complexes":["PAF1 complex (PAF1C)"],"partners":["PAF1","CTR9","RTF1","MYC","CSB/ERCC6","CDK12"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8WVC0","full_name":"RNA polymerase-associated protein LEO1","aliases":["Replicative senescence down-regulated leo1-like protein"],"length_aa":666,"mass_kda":75.4,"function":"Component of the PAF1 complex (PAF1C) which has multiple functions during transcription by RNA polymerase II and is implicated in regulation of development and maintenance of embryonic stem cell pluripotency. PAF1C associates with RNA polymerase II through interaction with POLR2A CTD non-phosphorylated and 'Ser-2'- and 'Ser-5'-phosphorylated forms and is involved in transcriptional elongation, acting both independently and synergistically with TCEA1 and in cooperation with the DSIF complex and HTATSF1. PAF1C is required for transcription of Hox and Wnt target genes. PAF1C is involved in hematopoiesis and stimulates transcriptional activity of KMT2A/MLL1; it promotes leukemogenesis through association with KMT2A/MLL1-rearranged oncoproteins, such as KMT2A/MLL1-MLLT3/AF9 and KMT2A/MLL1-MLLT1/ENL. PAF1C is involved in histone modifications such as ubiquitination of histone H2B and methylation on histone H3 'Lys-4' (H3K4me3). PAF1C recruits the RNF20/40 E3 ubiquitin-protein ligase complex and the E2 enzyme UBE2A or UBE2B to chromatin which mediate monoubiquitination of 'Lys-120' of histone H2B (H2BK120ub1); UB2A/B-mediated H2B ubiquitination is proposed to be coupled to transcription. PAF1C is involved in mRNA 3' end formation probably through association with cleavage and poly(A) factors. In case of infection by influenza A strain H3N2, PAF1C associates with viral NS1 protein, thereby regulating gene transcription. Involved in polyadenylation of mRNA precursors. Connects PAF1C to Wnt signaling","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/Q8WVC0/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/LEO1","classification":"Not Classified","n_dependent_lines":129,"n_total_lines":1208,"dependency_fraction":0.10678807947019868},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"ACTB","stoichiometry":0.2},{"gene":"CPSF6","stoichiometry":0.2},{"gene":"CSNK2B","stoichiometry":0.2},{"gene":"HIST2H2BE","stoichiometry":0.2},{"gene":"PTGES3","stoichiometry":0.2},{"gene":"SNRPA","stoichiometry":0.2},{"gene":"SNRPB","stoichiometry":0.2},{"gene":"SNRPC","stoichiometry":0.2},{"gene":"SNRPF","stoichiometry":0.2},{"gene":"SRP9","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/LEO1","total_profiled":1310},"omim":[{"mim_id":"620533","title":"LONG INTERGENIC NONCODING RNA 520; LINC00520","url":"https://www.omim.org/entry/620533"},{"mim_id":"610507","title":"LEO1 HOMOLOG, PAF1/RNA POLYMERASE II COMPLEX COMPONENT; LEO1","url":"https://www.omim.org/entry/610507"},{"mim_id":"610506","title":"PAF1 HOMOLOG, PAF1/RNA POLYMERASE II COMPLEX COMPONENT; PAF1","url":"https://www.omim.org/entry/610506"},{"mim_id":"609366","title":"CTR9 HOMOLOG, PAF1/RNA POLYMERASE II COMPLEX COMPONENT; CTR9","url":"https://www.omim.org/entry/609366"},{"mim_id":"607393","title":"CELL DIVISION CYCLE 73; CDC73","url":"https://www.omim.org/entry/607393"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoplasm","reliability":"Enhanced"},{"location":"Nucleoli fibrillar center","reliability":"Enhanced"},{"location":"Centrosome","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/LEO1"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"Q8WVC0","domains":[{"cath_id":"-","chopping":"373-512","consensus_level":"high","plddt":81.0883,"start":373,"end":512}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8WVC0","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8WVC0-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8WVC0-F1-predicted_aligned_error_v6.png","plddt_mean":54.28},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=LEO1","jax_strain_url":"https://www.jax.org/strain/search?query=LEO1"},"sequence":{"accession":"Q8WVC0","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8WVC0.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8WVC0/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8WVC0"}},"corpus_meta":[{"pmid":"11884586","id":"PMC_11884586","title":"Ctr9, Rtf1, and Leo1 are components of the Paf1/RNA polymerase II complex.","date":"2002","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/11884586","citation_count":206,"is_preprint":false},{"pmid":"26518661","id":"PMC_26518661","title":"The Paf1 complex factors Leo1 and Paf1 promote local histone turnover to modulate chromatin states in fission yeast.","date":"2015","source":"EMBO reports","url":"https://pubmed.ncbi.nlm.nih.gov/26518661","citation_count":68,"is_preprint":false},{"pmid":"20178782","id":"PMC_20178782","title":"The PAF1 complex component Leo1 is essential for cardiac and neural crest development in zebrafish.","date":"2010","source":"Developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/20178782","citation_count":49,"is_preprint":false},{"pmid":"20732871","id":"PMC_20732871","title":"Leo1 subunit of the yeast paf1 complex binds RNA and contributes to complex recruitment.","date":"2010","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/20732871","citation_count":39,"is_preprint":false},{"pmid":"24686170","id":"PMC_24686170","title":"LEO1 is regulated by PRL-3 and mediates its oncogenic properties in acute myelogenous leukemia.","date":"2014","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/24686170","citation_count":28,"is_preprint":false},{"pmid":"29078288","id":"PMC_29078288","title":"PAF1 complex component Leo1 helps recruit Drosophila Myc to promoters.","date":"2017","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/29078288","citation_count":28,"is_preprint":false},{"pmid":"37205756","id":"PMC_37205756","title":"CDK12 and Integrator-PP2A complex modulates LEO1 phosphorylation for processive transcription elongation.","date":"2023","source":"Science advances","url":"https://pubmed.ncbi.nlm.nih.gov/37205756","citation_count":24,"is_preprint":false},{"pmid":"20196086","id":"PMC_20196086","title":"Integrated genomic profiling identifies candidate genes implicated in glioma-genesis and a novel LEO1-SLC12A1 fusion gene.","date":"2010","source":"Genes, chromosomes & cancer","url":"https://pubmed.ncbi.nlm.nih.gov/20196086","citation_count":22,"is_preprint":false},{"pmid":"15791002","id":"PMC_15791002","title":"Expression of the Leo1-like domain of replicative senescence down-regulated Leo1-like (RDL) protein promotes senescence of 2BS fibroblasts.","date":"2005","source":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","url":"https://pubmed.ncbi.nlm.nih.gov/15791002","citation_count":17,"is_preprint":false},{"pmid":"34096589","id":"PMC_34096589","title":"LEO1 is a partner for Cockayne syndrome protein B (CSB) in response to transcription-blocking DNA damage.","date":"2021","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/34096589","citation_count":16,"is_preprint":false},{"pmid":"8018723","id":"PMC_8018723","title":"The gene LEO1 on yeast chromosome XV encodes a non-essential, extremely hydrophilic protein.","date":"1994","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/8018723","citation_count":14,"is_preprint":false},{"pmid":"40993282","id":"PMC_40993282","title":"LEO1 haploinsufficiency is associated with developmental delays and autism spectrum disorder.","date":"2025","source":"Journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/40993282","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":6978,"output_tokens":2316,"usd":0.027837,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9496,"output_tokens":2608,"usd":0.05634,"stage2_stop_reason":"end_turn"},"total_usd":0.084177,"stage1_batch_id":"msgbatch_01BbTCMyrRPyhtEq6b1MdwCN","stage2_batch_id":"msgbatch_011dEed5bbxYvTAaQWKJevxu","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2002,\n      \"finding\": \"Leo1 (along with Ctr9 and Rtf1) is a component of the Paf1/RNA Polymerase II complex in S. cerevisiae, distinct from the Srb-mediator form of Pol II holoenzyme. Deletion of LEO1 suppresses many paf1Δ phenotypes (e.g., restores CLN1 expression), indicating Leo1 participates in the same functional complex as Paf1.\",\n      \"method\": \"Tandem affinity purification, mass spectrometry, genetic epistasis (double-mutant analysis)\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — biochemical purification with mass spectrometry plus genetic epistasis, foundational study replicated by subsequent work\",\n      \"pmids\": [\"11884586\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The Leo1 subunit of the yeast Paf1 complex directly binds RNA in vitro. In vivo RNA-IP showed that Leo1, but not Rtf1, is necessary for Paf1C to associate with RNA. Cells lacking Leo1 show reduced Paf1C recruitment to transcribed chromatin and decreased levels of histone H3 and H3K4me3, suggesting Leo1-RNA interaction stabilizes complex localization at actively transcribed regions to influence chromatin structure.\",\n      \"method\": \"In vitro RNA-binding assay with purified protein, RNA immunoprecipitation (RNA-IP) in vivo, ChIP\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro reconstitution of RNA binding combined with in vivo RNA-IP and ChIP, multiple orthogonal methods in a single study\",\n      \"pmids\": [\"20732871\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"In fission yeast, the Leo1-Paf1 subcomplex of Paf1C is required to prevent heterochromatin spreading into euchromatin. Deletion of Leo1 decreases nucleosome turnover at heterochromatin boundary regions, leading to stabilization of heterochromatin (increased H3K9me2), in an RNAi-independent manner.\",\n      \"method\": \"Genome-wide ChIP-exo for H3K9me2, random mutant screen, nucleosome turnover assays\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — high-resolution genome-wide ChIP-exo combined with nucleosome turnover assays and genetic loss-of-function, multiple orthogonal methods\",\n      \"pmids\": [\"26518661\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"In zebrafish, Leo1 is a nuclear protein; a mutant Leo1 lacking the nuclear localization signal is redistributed to the cytoplasm and causes defects in cardiomyocyte differentiation at the atrioventricular boundary and loss of neural crest cell populations, establishing a functional requirement for nuclear Leo1 in vertebrate development.\",\n      \"method\": \"Genetic screen, identification of loss-of-function mutant, subcellular localization (nuclear vs. cytoplasmic distribution), phenotypic analysis of cardiac and neural crest markers\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — genetic loss-of-function with defined cellular phenotypes and direct localization experiment, single lab\",\n      \"pmids\": [\"20178782\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In AML cells, PRL-3 (an oncogenic phosphatase) upregulates LEO1 expression by increasing JMJD2C histone demethylase occupancy on the LEO1 promoter, thereby reducing H3K9me3 repressive marks. LEO1 in turn stabilizes the PAF complex and maintains expression of SOX2 and SOX4 oncogenes; loss of LEO1 destabilizes the PAF complex and reverses PRL-3 oncogenic phenotypes.\",\n      \"method\": \"SILAC-based quantitative proteomics, ChIP for histone marks and JMJD2C, LEO1 knockdown/overexpression, PAF complex co-immunoprecipitation\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — SILAC proteomics plus ChIP plus Co-IP and functional KD, multiple methods but single lab\",\n      \"pmids\": [\"24686170\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In Drosophila, the PAF1 complex component Leo1 physically interacts with Myc and helps recruit Myc to target gene promoters. Because PAF1C is associated with active genes, Leo1 contributes to Myc targeting to open chromatin/active promoters.\",\n      \"method\": \"Co-immunoprecipitation / physical interaction assays, ChIP for Myc binding at target promoters with and without Leo1\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — physical interaction demonstrated and ChIP showing reduced Myc recruitment, single lab with two orthogonal methods\",\n      \"pmids\": [\"29078288\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CDK12 phosphorylates LEO1 (identified by chemical genetic and phosphoproteomic screening). Acute depletion of LEO1 or substitution of its CDK12 phosphorylation sites with alanine attenuates PAF1C association with elongating RNA Pol II and impairs processive transcription elongation. LEO1 is also dephosphorylated by the Integrator-PP2A complex (INTAC); depletion of INTAC promotes PAF1C–Pol II association, revealing antagonistic regulation of LEO1 phosphorylation by CDK12 and INTAC.\",\n      \"method\": \"Chemical genetic CDK12 inhibition, phosphoproteomic mass spectrometry, alanine-substitution mutagenesis, co-immunoprecipitation of PAF1C with Pol II, nascent transcription elongation assays\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — phosphoproteomic substrate identification validated by in-cell phospho-mutagenesis, Co-IP, and functional elongation assays; multiple orthogonal methods in one rigorous study\",\n      \"pmids\": [\"37205756\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"LEO1 directly interacts with Cockayne syndrome protein B (CSB/ERCC6) in vitro and co-exists in a common complex in human cells. Both proteins are recruited to sites of DNA damage. Following UVC or cisplatin treatment, LEO1 and CSB show a transcription-dependent, coordinated association with chromatin. LEO1 knockdown reduces CSB chromatin recruitment, increases UV/cisplatin sensitivity, impairs RNA synthesis recovery, and slows cyclobutane pyrimidine dimer excision; CSB absence similarly reduces LEO1 chromatin recruitment, indicating reciprocal functional dependence in transcription-coupled DNA repair.\",\n      \"method\": \"Yeast two-hybrid screening, in vitro direct interaction with purified recombinant proteins, co-immunoprecipitation in human cells, fluorescent recruitment to laser-induced DNA damage sites, cell fractionation (chromatin association), LEO1 knockdown/knockout functional assays (RNA synthesis recovery, CPD excision, clonogenic survival)\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (Y2H, in vitro reconstitution, Co-IP, live-cell imaging, functional KD/KO assays) in a single rigorous study\",\n      \"pmids\": [\"34096589\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"LEO1 is a core subunit of the RNA Polymerase II-associated PAF1 complex that stabilizes PAF1C on actively transcribed chromatin by directly binding nascent RNA, undergoes CDK12-mediated phosphorylation (opposed by the Integrator-PP2A complex) to regulate PAF1C association with elongating Pol II and processive transcription elongation, prevents heterochromatin spreading by promoting nucleosome turnover, helps recruit transcription factors such as Myc to active promoters, and partners with the DNA repair factor CSB in a reciprocal, transcription-dependent manner to facilitate transcription-coupled nucleotide excision repair.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"LEO1 is a core subunit of the RNA Polymerase II-associated PAF1 complex (PAF1C) that couples transcription elongation to chromatin structure and genome maintenance [#0, #1]. It anchors PAF1C on actively transcribed chromatin through direct binding to nascent RNA, and loss of LEO1 reduces PAF1C recruitment to transcribed regions along with histone H3 occupancy and H3K4me3 [#1]. LEO1 association with elongating Pol II is dynamically controlled by phosphorylation: CDK12 phosphorylates LEO1 to promote processive elongation, while the Integrator-PP2A (INTAC) complex dephosphorylates it, establishing antagonistic regulation of PAF1C-Pol II engagement [#6]. Through nucleosome turnover at heterochromatin boundaries, LEO1 prevents heterochromatin spreading into euchromatin independently of RNAi [#2]. Beyond elongation, LEO1 helps recruit sequence-specific factors such as Myc to active promoters [#5] and partners reciprocally with the Cockayne syndrome protein CSB/ERCC6 in a transcription-dependent manner to facilitate transcription-coupled nucleotide excision repair [#7]. Nuclear LEO1 is required for vertebrate development, including cardiomyocyte differentiation and neural crest maintenance [#3].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Establishing that Leo1 is a bona fide member of the Paf1/Pol II complex defined the protein's primary functional context as transcription rather than the Srb-mediator holoenzyme.\",\n      \"evidence\": \"Tandem affinity purification with mass spectrometry and genetic epistasis in S. cerevisiae\",\n      \"pmids\": [\"11884586\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular role of Leo1 within the complex unresolved\", \"No mechanism for how Leo1 contributes to Pol II function\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identifying Leo1 as the RNA-binding subunit explained how PAF1C is retained on actively transcribed chromatin and linked this to histone modification.\",\n      \"evidence\": \"In vitro RNA-binding with purified protein, in vivo RNA-IP, and ChIP in yeast\",\n      \"pmids\": [\"20732871\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"RNA sequence/structure specificity not defined\", \"Structural basis of RNA contact unknown\", \"Causal link between RNA binding and H3K4me3 indirect\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstrating that nuclear localization of Leo1 is required for vertebrate development extended its role from yeast transcription to organismal differentiation programs.\",\n      \"evidence\": \"Genetic loss-of-function mutant, NLS-deletion mislocalization, and cardiac/neural crest phenotyping in zebrafish\",\n      \"pmids\": [\"20178782\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular targets driving cardiac/neural crest defects not identified\", \"Whether phenotypes reflect PAF1C-dependent transcription unclear\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Placing LEO1 downstream of an oncogenic phosphatase and as a stabilizer of the PAF complex connected its transcriptional role to maintenance of oncogene expression in leukemia.\",\n      \"evidence\": \"SILAC proteomics, ChIP for histone marks/JMJD2C, and PAF complex Co-IP with LEO1 knockdown in AML cells\",\n      \"pmids\": [\"24686170\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs indirect control of SOX2/SOX4 not separated\", \"Single-lab finding\", \"Generality across cancer types untested\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Showing Leo1 physically interacts with Myc and aids its promoter recruitment revealed a mechanism by which PAF1C directs a transcription factor to active chromatin.\",\n      \"evidence\": \"Co-immunoprecipitation and Myc ChIP at target promoters with/without Leo1 in Drosophila\",\n      \"pmids\": [\"29078288\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs PAF1C-bridged interaction not resolved\", \"Mapped interaction interface unknown\", \"Single-lab data\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identifying a reciprocal LEO1-CSB partnership established a direct role for LEO1 in transcription-coupled nucleotide excision repair beyond canonical elongation.\",\n      \"evidence\": \"Y2H, in vitro reconstitution, Co-IP in human cells, laser-induced damage recruitment, and KD/KO functional repair assays\",\n      \"pmids\": [\"34096589\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural interface of LEO1-CSB undefined\", \"How PAF1C function intersects with NER machinery mechanistically unclear\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Defining LEO1 as a CDK12 substrate antagonized by INTAC explained how PAF1C-Pol II association and processive elongation are dynamically tuned by phosphorylation.\",\n      \"evidence\": \"Chemical genetic CDK12 inhibition, phosphoproteomics, alanine phospho-mutants, PAF1C-Pol II Co-IP, and nascent elongation assays in human cells\",\n      \"pmids\": [\"37205756\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific phospho-sites' structural effect on PAF1C binding unresolved\", \"Interplay between phosphoregulation and RNA-binding-mediated retention unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How LEO1's RNA-binding, phosphoregulation, transcription-factor recruitment, and DNA-repair functions are integrated within a single mechanistic framework remains open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural model of LEO1 within PAF1C on Pol II\", \"RNA-binding specificity uncharacterized\", \"Coordination of elongation and TC-NER roles unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [1, 7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 1, 6]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [7]}\n    ],\n    \"complexes\": [\"PAF1 complex (PAF1C)\"],\n    \"partners\": [\"PAF1\", \"CTR9\", \"RTF1\", \"MYC\", \"CSB/ERCC6\", \"CDK12\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}