{"gene":"MED17","run_date":"2026-06-10T02:59:50","timeline":{"discoveries":[{"year":1998,"finding":"A functional interaction between Med6 and Srb4 (Med17) is required for transcriptional activation by RNA Pol II. A dominant, allele-specific suppressor screen identified an SRB4 allele that suppresses med6-ts transcriptional defects, and biochemical fractionation showed Med6 and Srb4 co-purify in the same Mediator subcomplex.","method":"Genetic suppressor screen (allele-specific suppression), biochemical Mediator subcomplex fractionation","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal genetic and biochemical evidence, allele-specific suppression demonstrating direct functional interaction, replicated by subcomplex co-purification","pmids":["9710620"],"is_preprint":false},{"year":2006,"finding":"The srb4-138 (Med17) temperature-sensitive allele causes dissociation of the Mediator complex at the head/middle domain boundary. Both head and middle sub-complexes can independently associate with RNA polymerase II, but at non-permissive temperature the head domain (containing Med17) is lost from active promoters, explaining the global cessation of RNA Pol II transcription.","method":"Biochemical purification of Mediator from mutant yeast strains, chromatin immunoprecipitation (ChIP) at permissive and non-permissive temperatures","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (biochemical fractionation + ChIP), mechanistically explains a well-established allele, single lab but rigorous","pmids":["16962561"],"is_preprint":false},{"year":2010,"finding":"The p.L371P missense mutation in human MED17 (corresponding to SRB4 in S. cerevisiae) inactivates the protein function, as demonstrated by complementation failure in yeast carrying the homologous mutation.","method":"Yeast complementation assay with the corresponding S. cerevisiae SRB4 mutation","journal":"American journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — complementation assay is a clean functional test but performed in a single study with no additional orthogonal mechanistic methods","pmids":["20950787"],"is_preprint":false},{"year":2012,"finding":"Med17 (Srb4) is a direct target of histone H4 tail interactions within the Mediator complex, as identified by UV photo-crosslinking with histone tail peptides containing a UV-activatable amino acid analog crosslinker.","method":"UV photo-crosslinking with synthetic histone tail peptides substituted with a crosslinkable amino acid analog; Mediator purified from mutant yeast strains","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct crosslinking method (in vitro) demonstrates physical contact, but single lab and limited orthogonal validation","pmids":["22693636"],"is_preprint":false},{"year":2014,"finding":"Human MED17 (hMED17) physically interacts with RNA Pol II and the general transcription factors TFIIB, TBP, TFIIE, and TFIIH via pulldown assays, and supports transcriptional activation in cells. Additionally, hMED17 binds the DNA helicase/TFIIH subunit XPB (required for NER), and also binds XPG in vitro. Upon UV-C irradiation, hMED17 colocalizes with NER factors XPB and XPG in the nucleus and associates with p53, suggesting a role in switching between transcription and nucleotide excision repair.","method":"Pulldown assays, luciferase reporter assays in hMED17-knockdown cells, immunofluorescence co-localization after UV-C irradiation, in vitro binding assays","journal":"Genes to cells : devoted to molecular & cellular mechanisms","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — multiple orthogonal methods (pulldown, reporter assay, KD, co-localization, in vitro binding), single lab","pmids":["25482373"],"is_preprint":false},{"year":2014,"finding":"Hepatic TRAP80 (MED17) selectively promotes LXR-dependent transcription of SREBP-1c but not ABCA1. Adenovirus-mediated shTRAP80 knockdown inhibited RNA Pol II recruitment to the LXRE of SREBP-1c but not to the LXRE of ABCA1, and liver-specific TRAP80 knockdown in mice ameliorated LXR-induced liver steatosis and hypertriglyceridemia while preserving reverse cholesterol transport.","method":"shRNA knockdown in human hepatic cell lines, adenovirus-mediated liver-specific knockdown in mice, ChIP for RNA Pol II at LXREs, in vivo metabolic phenotyping","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (ChIP, KD in cells and in vivo mouse model), promoter-specific mechanistic resolution between SREBP-1c and ABCA1 targets","pmids":["25437875"],"is_preprint":false},{"year":2017,"finding":"MED17 is phosphorylated at Ser53 by casein kinase 2 (CK2) in response to insulin/feeding conditions in hepatocytes and mouse liver, and this phosphorylation is required for insulin-stimulated transcriptional activation of lipogenic genes (e.g., FASN). MED17 directly interacts with the transcription factor USF1 at the FASN promoter to recruit Mediator and Pol II. Additionally, p38 MAPK phosphorylates MED17 at Thr570, and CK2-mediated phosphorylation at Ser53 only occurs in the absence of this p38-mediated event.","method":"Co-immunoprecipitation (MED17-USF1 interaction), phosphorylation mapping by site-directed mutagenesis (S53A non-phosphorylatable mutant), in vitro CK2 kinase assay, knockdown/overexpression in hepatocytes and adenovirus-mediated mouse liver studies, triglyceride/fatty acid synthesis assays","journal":"Science signaling","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro kinase assay with mutagenesis, Co-IP, KD/OE in cells and in vivo mouse model, multiple orthogonal methods across cell and animal contexts","pmids":["28223413"],"is_preprint":false},{"year":2021,"finding":"The cell polarity kinase MARK2 (Par1b) directly phosphorylates MED17 at Ser152 in vitro, and phosphomimetic S152D-MED17 selectively enhances NF-κB transcriptional activity for a subset of transcripts, mimicking the effect of MARK2 activation, while S152A-MED17 antagonizes this effect. MED17 was identified as the ~80 kDa band co-immunoprecipitating with RelA (NF-κB) upon MARK2 overexpression.","method":"In vitro phosphorylation with recombinant MARK2, co-immunoprecipitation (MED17-RelA), site-directed mutagenesis (S152D/S152A), transcriptome analysis and transcript enrichment in cells expressing phosphomimetic/phosphodeficient MED17","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro kinase assay with recombinant enzyme, mutagenesis (phosphomimetic/null), Co-IP, and transcriptome validation, multiple orthogonal approaches in single study","pmids":["33596087"],"is_preprint":false},{"year":2021,"finding":"MED17 mutations cause increased unfolded protein responses (UPR) in patient-derived fibroblasts, characterized by upregulation of CHOP and ATF4 expression and increased basal phosphorylation of eIF2α.","method":"Patient fibroblast analysis: RT-qPCR for UPR genes (CHOP, ATF4), immunoblot for p-eIF2α","journal":"Neurogenetics","confidence":"Low","confidence_rationale":"Tier 3 / Weak — patient fibroblast biochemistry without mechanistic dissection of how MED17 mutations cause UPR; single lab, limited methods","pmids":["34392449"],"is_preprint":false}],"current_model":"MED17 (Srb4/TRAP80) is a head-module subunit of the Mediator complex that physically bridges the head and middle domains of Mediator and directly contacts RNA Pol II, TFIIB, TBP, TFIIE, and TFIIH to support preinitiation complex assembly; it is post-translationally regulated by CK2-mediated phosphorylation at Ser53 (activating lipogenic gene transcription in response to insulin) and MARK2-mediated phosphorylation at Ser152 (selectively enhancing NF-κB target transcription), while also directly engaging histone H4 tails, interacting with NER factors XPB and XPG after UV damage, and functioning as a selective coactivator for LXR-dependent SREBP-1c but not ABCA1 transcription in the liver."},"narrative":{"mechanistic_narrative":"MED17 (Srb4/TRAP80) is a head-module subunit of the Mediator complex that is essential for RNA Polymerase II transcription, structurally bridging the head and middle domains and serving as a hub for preinitiation complex assembly [PMID:9710620, PMID:16962561]. The temperature-sensitive srb4-138 allele dissociates Mediator at the head/middle boundary and causes loss of the head domain from active promoters, producing a global shutdown of Pol II transcription that establishes MED17 as architecturally indispensable to the complex [PMID:16962561]. Human MED17 directly contacts Pol II and the general transcription factors TFIIB, TBP, TFIIE, and TFIIH and supports transcriptional activation, and it also engages histone H4 tails within Mediator [PMID:22693636, PMID:25482373]. Beyond core transcription, MED17 connects to nucleotide excision repair: it binds the TFIIH helicase subunit XPB and the endonuclease XPG, and after UV-C irradiation colocalizes with these NER factors and associates with p53 [PMID:25482373]. MED17 is a selective coactivator whose target specificity is tuned by signal-dependent phosphorylation: CK2 phosphorylates Ser53 in response to insulin to drive lipogenic gene transcription through a direct interaction with USF1 at the FASN promoter, p38 MAPK phosphorylation at Thr570 gates this CK2 event, and MARK2 phosphorylates Ser152 to selectively enhance NF-κB (RelA) target transcription [PMID:28223413, PMID:33596087]. In the liver, MED17 selectively promotes LXR-dependent transcription of SREBP-1c but not ABCA1, controlling Pol II recruitment to specific LXREs and modulating steatosis and triglyceride metabolism in vivo [PMID:25437875]. Missense mutation of MED17 (p.L371P) inactivates the protein in a yeast complementation test [PMID:20950787].","teleology":[{"year":1998,"claim":"Established that Med17/Srb4 functions cooperatively with another Mediator subunit (Med6) as part of a defined subcomplex required for Pol II activation, placing it within the Mediator architecture rather than as an isolated factor.","evidence":"Allele-specific genetic suppressor screen plus biochemical Mediator subcomplex co-purification in yeast","pmids":["9710620"],"confidence":"High","gaps":["Did not resolve the structural basis of the Med6-Srb4 interaction","Did not define which activators depend on this interaction"]},{"year":2006,"claim":"Resolved why MED17 is essential by showing it holds the head and middle modules together, with loss of the head domain from promoters explaining the global cessation of Pol II transcription.","evidence":"Biochemical purification of Mediator from srb4-138 mutant yeast plus ChIP at permissive and non-permissive temperatures","pmids":["16962561"],"confidence":"High","gaps":["Did not provide atomic-resolution structure of the head/middle interface","Mechanism of head retention at active promoters not detailed"]},{"year":2010,"claim":"Linked human MED17 dysfunction to disease by demonstrating that a patient missense mutation abolishes the conserved protein function.","evidence":"Yeast complementation assay with the homologous SRB4 mutation","pmids":["20950787"],"confidence":"Medium","gaps":["Functional consequence tested only by surrogate yeast complementation, not in human cells","No mechanistic dissection of how the mutation alters Mediator function"]},{"year":2012,"claim":"Identified a direct contact between MED17 and histone H4 tails, suggesting how Mediator may read chromatin in the vicinity of promoters.","evidence":"UV photo-crosslinking with crosslinker-substituted histone tail peptides and yeast-purified Mediator","pmids":["22693636"],"confidence":"Medium","gaps":["In vitro crosslinking only; functional consequence of the H4 contact untested","No reciprocal or in-cell validation"]},{"year":2014,"claim":"Mapped human MED17's direct partners (Pol II, TFIIB, TBP, TFIIE, TFIIH) and revealed an unexpected role linking Mediator to nucleotide excision repair via XPB/XPG and p53 after UV damage.","evidence":"Pulldown and in vitro binding assays, luciferase reporters in knockdown cells, and immunofluorescence colocalization after UV-C irradiation","pmids":["25482373"],"confidence":"Medium","gaps":["NER role inferred from colocalization, not from direct repair assays","Single lab without reciprocal validation of all interactions"]},{"year":2014,"claim":"Demonstrated promoter-selective coactivation, showing MED17 distinguishes between LXR targets (SREBP-1c vs ABCA1) and thereby separates lipogenesis from reverse cholesterol transport in vivo.","evidence":"shRNA and adenoviral liver-specific knockdown, ChIP for Pol II at LXREs, and in vivo metabolic phenotyping in mice","pmids":["25437875"],"confidence":"High","gaps":["Molecular basis for promoter discrimination between SREBP-1c and ABCA1 not defined","Did not identify the MED17 region mediating LXRE selectivity"]},{"year":2017,"claim":"Established signal-dependent control of MED17 by showing CK2 phosphorylation at Ser53 (gated by p38 phosphorylation at Thr570) couples insulin signaling to lipogenic transcription through a direct USF1 interaction.","evidence":"In vitro CK2 kinase assay with S53A mutagenesis, Co-IP of MED17-USF1, and knockdown/overexpression in hepatocytes and mouse liver","pmids":["28223413"],"confidence":"High","gaps":["Structural effect of Ser53 phosphorylation on Mediator not resolved","Cross-talk logic between p38 and CK2 events only partially defined"]},{"year":2021,"claim":"Extended the phospho-regulation model by showing MARK2 phosphorylation of MED17 at Ser152 selectively tunes NF-κB target transcription, establishing MED17 as a node integrating polarity-kinase signaling with inflammatory gene programs.","evidence":"In vitro phosphorylation with recombinant MARK2, phosphomimetic/null mutagenesis, Co-IP with RelA, and transcriptome analysis","pmids":["33596087"],"confidence":"High","gaps":["Mechanism by which Ser152 phosphorylation selects specific NF-κB transcripts not defined","Physiological context of MARK2-MED17 signaling untested in vivo"]},{"year":2021,"claim":"Connected MED17 deficiency to a cellular stress phenotype by showing patient-mutant fibroblasts exhibit elevated unfolded protein responses.","evidence":"RT-qPCR for CHOP/ATF4 and immunoblot for p-eIF2α in patient-derived fibroblasts","pmids":["34392449"],"confidence":"Low","gaps":["No mechanistic link established between MED17 mutation and UPR activation","Single lab, descriptive biochemistry without rescue"]},{"year":null,"claim":"How MED17's multiple phosphorylation events and partner contacts are integrated to achieve gene-selective coactivation, and the structural basis for its promoter discrimination, remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model linking phospho-sites to Mediator conformation","Mechanism of promoter/target selectivity uncharacterized","Causal chain from human mutations to cellular phenotypes incomplete"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[0,1,4,5]},{"term_id":"GO:0042393","term_label":"histone binding","supporting_discovery_ids":[3]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[4,6]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[4]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,1,4]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[5,6]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[4]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[6,7]}],"complexes":["Mediator complex"],"partners":["MED6","TFIIB","TBP","USF1","RELA","XPB","XPG"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9NVC6","full_name":"Mediator of RNA polymerase II transcription subunit 17","aliases":["Activator-recruited cofactor 77 kDa component","ARC77","Cofactor required for Sp1 transcriptional activation subunit 6","CRSP complex subunit 6","Mediator complex subunit 17","Thyroid hormone receptor-associated protein complex 80 kDa component","Trap80","Transcriptional coactivator CRSP77","Vitamin D3 receptor-interacting protein complex 80 kDa component","DRIP80"],"length_aa":651,"mass_kda":72.9,"function":"Component of the Mediator complex, a coactivator involved in the regulated transcription of nearly all RNA polymerase II-dependent genes. Mediator functions as a bridge to convey information from gene-specific regulatory proteins to the basal RNA polymerase II transcription machinery. Mediator is recruited to promoters by direct interactions with regulatory proteins and serves as a scaffold for the assembly of a functional preinitiation complex with RNA polymerase II and the general transcription factors","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/Q9NVC6/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/MED17","classification":"Common Essential","n_dependent_lines":1187,"n_total_lines":1208,"dependency_fraction":0.9826158940397351},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000042429","cell_line_id":"CID000238","localizations":[{"compartment":"nuclear_punctae","grade":3},{"compartment":"nucleoplasm","grade":3}],"interactors":[{"gene":"MED10","stoichiometry":10.0},{"gene":"MED11","stoichiometry":10.0},{"gene":"MED14","stoichiometry":10.0},{"gene":"MED7","stoichiometry":10.0},{"gene":"IXL;MED29","stoichiometry":10.0},{"gene":"MED24","stoichiometry":10.0},{"gene":"MED20","stoichiometry":10.0},{"gene":"MED28","stoichiometry":10.0},{"gene":"MED12;TNRC11","stoichiometry":10.0},{"gene":"MED30","stoichiometry":10.0}],"url":"https://opencell.sf.czbiohub.org/target/CID000238","total_profiled":1310},"omim":[{"mim_id":"613668","title":"MICROCEPHALY, POSTNATAL PROGRESSIVE, WITH SEIZURES AND BRAIN ATROPHY","url":"https://www.omim.org/entry/613668"},{"mim_id":"612762","title":"SPTY7-LIKE, STAGA COMPLEX SUBUNIT GAMMA; SUPT7L","url":"https://www.omim.org/entry/612762"},{"mim_id":"612385","title":"MEDIATOR COMPLEX SUBUNIT 19; MED19","url":"https://www.omim.org/entry/612385"},{"mim_id":"611479","title":"GPN-LOOP GTPase 1; GPN1","url":"https://www.omim.org/entry/611479"},{"mim_id":"611477","title":"RNA POLYMERASE II-ASSOCIATED PROTEIN 3; RPAP3","url":"https://www.omim.org/entry/611477"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nuclear speckles","reliability":"Approved"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/MED17"},"hgnc":{"alias_symbol":["CRSP77","TRAP80","DRIP80","SRB4"],"prev_symbol":["CRSP6"]},"alphafold":{"accession":"Q9NVC6","domains":[{"cath_id":"-","chopping":"187-351_367-386","consensus_level":"high","plddt":81.4811,"start":187,"end":386},{"cath_id":"-","chopping":"430-516","consensus_level":"medium","plddt":92.6877,"start":430,"end":516},{"cath_id":"-","chopping":"532-647","consensus_level":"medium","plddt":85.4632,"start":532,"end":647}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NVC6","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NVC6-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NVC6-F1-predicted_aligned_error_v6.png","plddt_mean":78.56},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MED17","jax_strain_url":"https://www.jax.org/strain/search?query=MED17"},"sequence":{"accession":"Q9NVC6","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9NVC6.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9NVC6/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NVC6"}},"corpus_meta":[{"pmid":"9710620","id":"PMC_9710620","title":"Requirement for a functional interaction between mediator components Med6 and Srb4 in RNA polymerase II transcription.","date":"1998","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/9710620","citation_count":71,"is_preprint":false},{"pmid":"20950787","id":"PMC_20950787","title":"Infantile cerebral and cerebellar atrophy is associated with a mutation in the MED17 subunit of the transcription preinitiation mediator complex.","date":"2010","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/20950787","citation_count":65,"is_preprint":false},{"pmid":"25437875","id":"PMC_25437875","title":"Hepatic TRAP80 selectively regulates lipogenic activity of liver X receptor.","date":"2014","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/25437875","citation_count":28,"is_preprint":false},{"pmid":"16962561","id":"PMC_16962561","title":"The classical srb4-138 mutant allele causes dissociation of yeast Mediator.","date":"2006","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/16962561","citation_count":27,"is_preprint":false},{"pmid":"22693636","id":"PMC_22693636","title":"Med5(Nut1) and Med17(Srb4) are direct targets of mediator histone H4 tail interactions.","date":"2012","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/22693636","citation_count":25,"is_preprint":false},{"pmid":"28223413","id":"PMC_28223413","title":"Transcriptional activation of lipogenesis by insulin requires phosphorylation of MED17 by CK2.","date":"2017","source":"Science signaling","url":"https://pubmed.ncbi.nlm.nih.gov/28223413","citation_count":22,"is_preprint":false},{"pmid":"25482373","id":"PMC_25482373","title":"Human mediator MED17 subunit plays essential roles in gene regulation by associating with the transcription and DNA repair machineries.","date":"2014","source":"Genes to cells : devoted to molecular & cellular mechanisms","url":"https://pubmed.ncbi.nlm.nih.gov/25482373","citation_count":16,"is_preprint":false},{"pmid":"26004231","id":"PMC_26004231","title":"Distinct but milder phenotypes with choreiform movements in siblings with compound heterozygous mutations in the transcription preinitiation mediator complex subunit 17 (MED17).","date":"2015","source":"Brain & development","url":"https://pubmed.ncbi.nlm.nih.gov/26004231","citation_count":11,"is_preprint":false},{"pmid":"34392449","id":"PMC_34392449","title":"Increased unfolded protein responses caused by MED17 mutations.","date":"2021","source":"Neurogenetics","url":"https://pubmed.ncbi.nlm.nih.gov/34392449","citation_count":8,"is_preprint":false},{"pmid":"33756211","id":"PMC_33756211","title":"Delineation of the phenotype of MED17-related disease in Caucasus-Jewish families.","date":"2021","source":"European journal of paediatric neurology : EJPN : official journal of the European Paediatric Neurology Society","url":"https://pubmed.ncbi.nlm.nih.gov/33756211","citation_count":6,"is_preprint":false},{"pmid":"36508181","id":"PMC_36508181","title":"An expansion of phenotype: novel homozygous variant in the MED17 identified in patients with progressive microcephaly and global developmental delay.","date":"2022","source":"Journal of neurogenetics","url":"https://pubmed.ncbi.nlm.nih.gov/36508181","citation_count":5,"is_preprint":false},{"pmid":"33596087","id":"PMC_33596087","title":"The cell polarity kinase Par1b/MARK2 activation selects specific NF-kB transcripts via phosphorylation of core mediator Med17/TRAP80.","date":"2021","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/33596087","citation_count":4,"is_preprint":false},{"pmid":"39794604","id":"PMC_39794604","title":"Cu-tolerant Klebsiella variicola SRB-4 increased the nanoparticle (NP) stress resilience in garden peas (Pisum sativum L.) raised in soil polluted with varying doses of copper oxide (CuO)-NP.","date":"2025","source":"World journal of microbiology & biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/39794604","citation_count":4,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8270,"output_tokens":2632,"usd":0.032145,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9790,"output_tokens":3321,"usd":0.065988,"stage2_stop_reason":"end_turn"},"total_usd":0.098133,"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\": 1998,\n      \"finding\": \"A functional interaction between Med6 and Srb4 (Med17) is required for transcriptional activation by RNA Pol II. A dominant, allele-specific suppressor screen identified an SRB4 allele that suppresses med6-ts transcriptional defects, and biochemical fractionation showed Med6 and Srb4 co-purify in the same Mediator subcomplex.\",\n      \"method\": \"Genetic suppressor screen (allele-specific suppression), biochemical Mediator subcomplex fractionation\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal genetic and biochemical evidence, allele-specific suppression demonstrating direct functional interaction, replicated by subcomplex co-purification\",\n      \"pmids\": [\"9710620\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The srb4-138 (Med17) temperature-sensitive allele causes dissociation of the Mediator complex at the head/middle domain boundary. Both head and middle sub-complexes can independently associate with RNA polymerase II, but at non-permissive temperature the head domain (containing Med17) is lost from active promoters, explaining the global cessation of RNA Pol II transcription.\",\n      \"method\": \"Biochemical purification of Mediator from mutant yeast strains, chromatin immunoprecipitation (ChIP) at permissive and non-permissive temperatures\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (biochemical fractionation + ChIP), mechanistically explains a well-established allele, single lab but rigorous\",\n      \"pmids\": [\"16962561\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The p.L371P missense mutation in human MED17 (corresponding to SRB4 in S. cerevisiae) inactivates the protein function, as demonstrated by complementation failure in yeast carrying the homologous mutation.\",\n      \"method\": \"Yeast complementation assay with the corresponding S. cerevisiae SRB4 mutation\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — complementation assay is a clean functional test but performed in a single study with no additional orthogonal mechanistic methods\",\n      \"pmids\": [\"20950787\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Med17 (Srb4) is a direct target of histone H4 tail interactions within the Mediator complex, as identified by UV photo-crosslinking with histone tail peptides containing a UV-activatable amino acid analog crosslinker.\",\n      \"method\": \"UV photo-crosslinking with synthetic histone tail peptides substituted with a crosslinkable amino acid analog; Mediator purified from mutant yeast strains\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct crosslinking method (in vitro) demonstrates physical contact, but single lab and limited orthogonal validation\",\n      \"pmids\": [\"22693636\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Human MED17 (hMED17) physically interacts with RNA Pol II and the general transcription factors TFIIB, TBP, TFIIE, and TFIIH via pulldown assays, and supports transcriptional activation in cells. Additionally, hMED17 binds the DNA helicase/TFIIH subunit XPB (required for NER), and also binds XPG in vitro. Upon UV-C irradiation, hMED17 colocalizes with NER factors XPB and XPG in the nucleus and associates with p53, suggesting a role in switching between transcription and nucleotide excision repair.\",\n      \"method\": \"Pulldown assays, luciferase reporter assays in hMED17-knockdown cells, immunofluorescence co-localization after UV-C irradiation, in vitro binding assays\",\n      \"journal\": \"Genes to cells : devoted to molecular & cellular mechanisms\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — multiple orthogonal methods (pulldown, reporter assay, KD, co-localization, in vitro binding), single lab\",\n      \"pmids\": [\"25482373\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Hepatic TRAP80 (MED17) selectively promotes LXR-dependent transcription of SREBP-1c but not ABCA1. Adenovirus-mediated shTRAP80 knockdown inhibited RNA Pol II recruitment to the LXRE of SREBP-1c but not to the LXRE of ABCA1, and liver-specific TRAP80 knockdown in mice ameliorated LXR-induced liver steatosis and hypertriglyceridemia while preserving reverse cholesterol transport.\",\n      \"method\": \"shRNA knockdown in human hepatic cell lines, adenovirus-mediated liver-specific knockdown in mice, ChIP for RNA Pol II at LXREs, in vivo metabolic phenotyping\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (ChIP, KD in cells and in vivo mouse model), promoter-specific mechanistic resolution between SREBP-1c and ABCA1 targets\",\n      \"pmids\": [\"25437875\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"MED17 is phosphorylated at Ser53 by casein kinase 2 (CK2) in response to insulin/feeding conditions in hepatocytes and mouse liver, and this phosphorylation is required for insulin-stimulated transcriptional activation of lipogenic genes (e.g., FASN). MED17 directly interacts with the transcription factor USF1 at the FASN promoter to recruit Mediator and Pol II. Additionally, p38 MAPK phosphorylates MED17 at Thr570, and CK2-mediated phosphorylation at Ser53 only occurs in the absence of this p38-mediated event.\",\n      \"method\": \"Co-immunoprecipitation (MED17-USF1 interaction), phosphorylation mapping by site-directed mutagenesis (S53A non-phosphorylatable mutant), in vitro CK2 kinase assay, knockdown/overexpression in hepatocytes and adenovirus-mediated mouse liver studies, triglyceride/fatty acid synthesis assays\",\n      \"journal\": \"Science signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro kinase assay with mutagenesis, Co-IP, KD/OE in cells and in vivo mouse model, multiple orthogonal methods across cell and animal contexts\",\n      \"pmids\": [\"28223413\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The cell polarity kinase MARK2 (Par1b) directly phosphorylates MED17 at Ser152 in vitro, and phosphomimetic S152D-MED17 selectively enhances NF-κB transcriptional activity for a subset of transcripts, mimicking the effect of MARK2 activation, while S152A-MED17 antagonizes this effect. MED17 was identified as the ~80 kDa band co-immunoprecipitating with RelA (NF-κB) upon MARK2 overexpression.\",\n      \"method\": \"In vitro phosphorylation with recombinant MARK2, co-immunoprecipitation (MED17-RelA), site-directed mutagenesis (S152D/S152A), transcriptome analysis and transcript enrichment in cells expressing phosphomimetic/phosphodeficient MED17\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro kinase assay with recombinant enzyme, mutagenesis (phosphomimetic/null), Co-IP, and transcriptome validation, multiple orthogonal approaches in single study\",\n      \"pmids\": [\"33596087\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"MED17 mutations cause increased unfolded protein responses (UPR) in patient-derived fibroblasts, characterized by upregulation of CHOP and ATF4 expression and increased basal phosphorylation of eIF2α.\",\n      \"method\": \"Patient fibroblast analysis: RT-qPCR for UPR genes (CHOP, ATF4), immunoblot for p-eIF2α\",\n      \"journal\": \"Neurogenetics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — patient fibroblast biochemistry without mechanistic dissection of how MED17 mutations cause UPR; single lab, limited methods\",\n      \"pmids\": [\"34392449\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MED17 (Srb4/TRAP80) is a head-module subunit of the Mediator complex that physically bridges the head and middle domains of Mediator and directly contacts RNA Pol II, TFIIB, TBP, TFIIE, and TFIIH to support preinitiation complex assembly; it is post-translationally regulated by CK2-mediated phosphorylation at Ser53 (activating lipogenic gene transcription in response to insulin) and MARK2-mediated phosphorylation at Ser152 (selectively enhancing NF-κB target transcription), while also directly engaging histone H4 tails, interacting with NER factors XPB and XPG after UV damage, and functioning as a selective coactivator for LXR-dependent SREBP-1c but not ABCA1 transcription in the liver.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"MED17 (Srb4/TRAP80) is a head-module subunit of the Mediator complex that is essential for RNA Polymerase II transcription, structurally bridging the head and middle domains and serving as a hub for preinitiation complex assembly [#0, #1]. The temperature-sensitive srb4-138 allele dissociates Mediator at the head/middle boundary and causes loss of the head domain from active promoters, producing a global shutdown of Pol II transcription that establishes MED17 as architecturally indispensable to the complex [#1]. Human MED17 directly contacts Pol II and the general transcription factors TFIIB, TBP, TFIIE, and TFIIH and supports transcriptional activation, and it also engages histone H4 tails within Mediator [#3, #4]. Beyond core transcription, MED17 connects to nucleotide excision repair: it binds the TFIIH helicase subunit XPB and the endonuclease XPG, and after UV-C irradiation colocalizes with these NER factors and associates with p53 [#4]. MED17 is a selective coactivator whose target specificity is tuned by signal-dependent phosphorylation: CK2 phosphorylates Ser53 in response to insulin to drive lipogenic gene transcription through a direct interaction with USF1 at the FASN promoter, p38 MAPK phosphorylation at Thr570 gates this CK2 event, and MARK2 phosphorylates Ser152 to selectively enhance NF-κB (RelA) target transcription [#6, #7]. In the liver, MED17 selectively promotes LXR-dependent transcription of SREBP-1c but not ABCA1, controlling Pol II recruitment to specific LXREs and modulating steatosis and triglyceride metabolism in vivo [#5]. Missense mutation of MED17 (p.L371P) inactivates the protein in a yeast complementation test [#2].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Established that Med17/Srb4 functions cooperatively with another Mediator subunit (Med6) as part of a defined subcomplex required for Pol II activation, placing it within the Mediator architecture rather than as an isolated factor.\",\n      \"evidence\": \"Allele-specific genetic suppressor screen plus biochemical Mediator subcomplex co-purification in yeast\",\n      \"pmids\": [\"9710620\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve the structural basis of the Med6-Srb4 interaction\", \"Did not define which activators depend on this interaction\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Resolved why MED17 is essential by showing it holds the head and middle modules together, with loss of the head domain from promoters explaining the global cessation of Pol II transcription.\",\n      \"evidence\": \"Biochemical purification of Mediator from srb4-138 mutant yeast plus ChIP at permissive and non-permissive temperatures\",\n      \"pmids\": [\"16962561\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not provide atomic-resolution structure of the head/middle interface\", \"Mechanism of head retention at active promoters not detailed\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Linked human MED17 dysfunction to disease by demonstrating that a patient missense mutation abolishes the conserved protein function.\",\n      \"evidence\": \"Yeast complementation assay with the homologous SRB4 mutation\",\n      \"pmids\": [\"20950787\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence tested only by surrogate yeast complementation, not in human cells\", \"No mechanistic dissection of how the mutation alters Mediator function\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identified a direct contact between MED17 and histone H4 tails, suggesting how Mediator may read chromatin in the vicinity of promoters.\",\n      \"evidence\": \"UV photo-crosslinking with crosslinker-substituted histone tail peptides and yeast-purified Mediator\",\n      \"pmids\": [\"22693636\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vitro crosslinking only; functional consequence of the H4 contact untested\", \"No reciprocal or in-cell validation\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Mapped human MED17's direct partners (Pol II, TFIIB, TBP, TFIIE, TFIIH) and revealed an unexpected role linking Mediator to nucleotide excision repair via XPB/XPG and p53 after UV damage.\",\n      \"evidence\": \"Pulldown and in vitro binding assays, luciferase reporters in knockdown cells, and immunofluorescence colocalization after UV-C irradiation\",\n      \"pmids\": [\"25482373\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"NER role inferred from colocalization, not from direct repair assays\", \"Single lab without reciprocal validation of all interactions\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Demonstrated promoter-selective coactivation, showing MED17 distinguishes between LXR targets (SREBP-1c vs ABCA1) and thereby separates lipogenesis from reverse cholesterol transport in vivo.\",\n      \"evidence\": \"shRNA and adenoviral liver-specific knockdown, ChIP for Pol II at LXREs, and in vivo metabolic phenotyping in mice\",\n      \"pmids\": [\"25437875\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis for promoter discrimination between SREBP-1c and ABCA1 not defined\", \"Did not identify the MED17 region mediating LXRE selectivity\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Established signal-dependent control of MED17 by showing CK2 phosphorylation at Ser53 (gated by p38 phosphorylation at Thr570) couples insulin signaling to lipogenic transcription through a direct USF1 interaction.\",\n      \"evidence\": \"In vitro CK2 kinase assay with S53A mutagenesis, Co-IP of MED17-USF1, and knockdown/overexpression in hepatocytes and mouse liver\",\n      \"pmids\": [\"28223413\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural effect of Ser53 phosphorylation on Mediator not resolved\", \"Cross-talk logic between p38 and CK2 events only partially defined\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Extended the phospho-regulation model by showing MARK2 phosphorylation of MED17 at Ser152 selectively tunes NF-κB target transcription, establishing MED17 as a node integrating polarity-kinase signaling with inflammatory gene programs.\",\n      \"evidence\": \"In vitro phosphorylation with recombinant MARK2, phosphomimetic/null mutagenesis, Co-IP with RelA, and transcriptome analysis\",\n      \"pmids\": [\"33596087\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which Ser152 phosphorylation selects specific NF-κB transcripts not defined\", \"Physiological context of MARK2-MED17 signaling untested in vivo\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Connected MED17 deficiency to a cellular stress phenotype by showing patient-mutant fibroblasts exhibit elevated unfolded protein responses.\",\n      \"evidence\": \"RT-qPCR for CHOP/ATF4 and immunoblot for p-eIF2α in patient-derived fibroblasts\",\n      \"pmids\": [\"34392449\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No mechanistic link established between MED17 mutation and UPR activation\", \"Single lab, descriptive biochemistry without rescue\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How MED17's multiple phosphorylation events and partner contacts are integrated to achieve gene-selective coactivation, and the structural basis for its promoter discrimination, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model linking phospho-sites to Mediator conformation\", \"Mechanism of promoter/target selectivity uncharacterized\", \"Causal chain from human mutations to cellular phenotypes incomplete\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 1, 4, 5]},\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [4, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 1, 4]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [5, 6]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [6, 7]}\n    ],\n    \"complexes\": [\"Mediator complex\"],\n    \"partners\": [\"MED6\", \"TFIIB\", \"TBP\", \"USF1\", \"RELA\", \"XPB\", \"XPG\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}