Affinage

MED6

Mediator of RNA polymerase II transcription subunit 6 · UniProt O75586

Length
246 aa
Mass
28.4 kDa
Annotated
2026-06-10
34 papers in source corpus 21 papers cited in narrative 21 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 5/5 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

MED6 is an essential, evolutionarily conserved subunit of the Mediator co-activator complex that is required for transcriptional activation from most RNA polymerase II (class II) promoters in vivo, where it acts downstream of Mediator recruitment to enable formation of the transcription initiation complex (PMID:9234719, PMID:29992056). Structurally, MED6 resides in the Mediator head module and serves as a physical bridge that tethers the middle module to the head module, with its terminal regions clamping the head–middle interface and its shoulder domain making direct contact with the Pol II C-terminal domain (CTD) (PMID:15710619, PMID:23123849, PMID:28467824, PMID:37014863). Functionally, MED6 is a convergence point onto which diverse activator-specific signals are channeled before being transmitted to the basal machinery, since it is required for activation by every activator tested while neighboring subunits show activator-selective requirements (PMID:9891034); signal transmission to the basal apparatus depends on a genetically and biochemically defined interaction with Srb4/MED17 (PMID:9710620, PMID:9671455) and connection to the middle module through MED21 (PMID:16758199). Mediator's regulatory output is bidirectional and context-dependent: MED6-containing complexes can repress activated transcription, and CDK8-kinase-containing versus kinase-free MED6 subcomplexes differentially couple CTD phosphorylation to activation (PMID:9734358, PMID:10024883, PMID:17212659). This activity is conserved and developmentally essential across metazoa, where MED6 is required for cell proliferation and for the transcriptional output of Ras and Wnt signaling (PMID:11438678, PMID:11688559, PMID:15790964).

Mechanistic history

Synthesis pass · year-by-year structured walk · 15 steps
  1. 1997 High

    Established that MED6 is not a generic structural subunit but is specifically required for activated (not basal) transcription, localizing its function to initiation complex formation.

    Evidence Temperature-sensitive yeast mutant with in vivo transcription and reconstituted in vitro transcription assays

    PMID:9234719

    Open questions at the time
    • Did not define which protein contacts mediate the initiation defect
    • Mechanism of activator selectivity not addressed
  2. 1998 High

    Showed MED6 function is conserved in mammals and linked it to CTD biology, demonstrating Mediator binds the Pol II CTD and stimulates its phosphorylation by TFIIH.

    Evidence Biochemical purification of mouse Mediator with CTD binding and TFIIH-dependent CTD phosphorylation assays

    PMID:9671713

    Open questions at the time
    • Did not assign the CTD contact to MED6 specifically
    • Direct vs. indirect role of MED6 in phosphorylation unresolved
  3. 1998 High

    Identified the functional partner through which MED6 transmits activation signals, placing MED6 and Srb4 in the same Mediator subcomplex with a genetically required interaction.

    Evidence Allele-specific dominant suppressor screen plus biochemical Mediator subcomplex fractionation in yeast; complementary suppressor and Co-IP analysis with Srb4

    PMID:9671455 PMID:9710620

    Open questions at the time
    • Atomic basis of the MED6–Srb4 interaction not defined
    • Whether the interaction is direct or bridged by other subunits not resolved
  4. 1999 High

    Demonstrated that MED6-containing human Mediator can both repress and synergistically enhance activator-dependent transcription, revealing bidirectional, context-dependent regulatory output.

    Evidence Biochemical purification of human NAT and SMCC complexes with in vitro repression/activation and CTD-independent activator interaction assays

    PMID:10024883 PMID:9734358

    Open questions at the time
    • MED6-specific contribution to repression vs activation not isolated
    • Switch between repressive and activating states not mechanistically defined
  5. 1999 Medium

    Distinguished MED6 from other Mediator subunits as a universal activation requirement, establishing it as a convergence point for diverse activation signals.

    Evidence Differential display and Northern analysis across multiple activator systems (Bas1/Bas2, Gcn4, Gal4, Rap1) in Mediator mutant strains

    PMID:9891034

    Open questions at the time
    • Convergence interpreted from genetic requirement, not direct activator-MED6 contacts
    • Does not explain how distinct signals are mechanistically integrated
  6. 2001 Medium

    Showed MED6 function is required for metazoan viability, proliferation, and the transcriptional readout of specific developmental signaling pathways.

    Evidence Drosophila loss-of-function mutants with microarray/RT-PCR; C. elegans RNAi epistasis with Ras and Wnt pathway alleles

    PMID:11438678 PMID:11688559

    Open questions at the time
    • Selectivity for some but not all genes left unexplained at the mechanistic level
    • Direct vs indirect role in pathway-specific transcription not separated
  7. 2005 High

    Provided the first structural rationale for MED6 as the module bridge, showing it binds the MED7·MED21 surface to connect the middle and head modules.

    Evidence X-ray crystallography (3.0 Å) of MED7·MED21 with binding-surface analysis; in vivo Co-IP of the LET-425/MED6 Mediator complex in C. elegans

    PMID:15710619 PMID:15790964

    Open questions at the time
    • Conformational role inferred from structure, not directly observed during activation
    • Functional consequence of bridging not yet perturbed
  8. 2006 Medium

    Defined the molecular route by which MED6 connects to the middle module, identifying MED21 as the direct middle-module link.

    Evidence Two-hybrid and Co-IP in insect cells and E. coli plus high-copy suppressor screen

    PMID:16758199

    Open questions at the time
    • Functional consequences of the MED6–MED21 interaction not tested
    • Single biochemical study without structural localization of the contact
  9. 2007 Medium

    Showed that the kinase content of MED6 subcomplexes determines whether activation is coupled to Pol II phosphorylation, dissecting activation from CTD modification.

    Evidence Affinity purification of MED6/MED7/CDK8 subcomplexes (TMLC1 vs TMLC3) with in vitro transcription, kinase, and GTF interaction assays

    PMID:17212659

    Open questions at the time
    • MED6's specific catalytic vs scaffolding role in each complex not separated
    • Single-lab biochemical fractionation
  10. 2010 Medium

    Resolved the recruitment hierarchy at a target promoter, showing MED14 (not MED1) positions MED6 at proximal promoters.

    Evidence ChIP with siRNA knockdown of MED1 and MED14 at the PPARγ target Fabp4

    PMID:20194623

    Open questions at the time
    • Generality beyond Fabp4 not established
    • Mechanism by which MED14 positions MED6 not structurally defined
  11. 2012 High

    Placed MED6 precisely within the seven-subunit head module architecture that contacts Pol II, refining its structural role.

    Evidence X-ray crystallography (3.4 Å) of the S. pombe Mediator head module

    PMID:23123849

    Open questions at the time
    • Static structure does not capture dynamics during initiation
    • Does not directly map activator signals onto MED6
  12. 2017 High

    Confirmed MED6 terminal regions as the functionally critical head–middle tether and integrated MED6 into a PIC-Mediator model linking it to TFIIH kinase contacts.

    Evidence X-ray crystallography (3.4 Å) of 15-subunit core Mediator with crosslinking MS and cryo-EM PIC model integration; mutation clustering at the head-middle interface

    PMID:28467824

    Open questions at the time
    • Causal contribution of MED6 tether to activation kinetics not measured
    • How CTD contacts are remodeled during transcription unresolved
  13. 2018 Medium

    Genetically separated MED6's recruitment role from its post-recruitment function, defining an internal region essential after Mediator is already on the promoter.

    Evidence Internal deletion mutagenesis (Δ6, Δ2) with LexA artificial recruitment, in vitro transcription complementation, Western blot and ChIP

    PMID:29992056

    Open questions at the time
    • Molecular event triggered by the essential region not identified
    • Single-lab study with limited replication
  14. 2023 High

    Pinpointed the atomic CTD-Mediator contact, showing the Pol II CTD binds between the MED6 shoulder and MED31 knob domains.

    Evidence Cryo-EM and atomic model of yeast PIC-Mediator

    PMID:37014863

    Open questions at the time
    • Functional requirement of the shoulder-CTD contact not tested by mutation
    • Dynamics of CTD handoff to TFIIH kinase not resolved
  15. 2023 Low

    Linked MED6 to repression of a specific transcriptional program, showing its loss derepresses lipid droplet biogenesis genes in cancer cells.

    Evidence shRNA knockdown with lipid droplet FACS and expression analysis of PLIN2/DGAT1

    PMID:37983968

    Open questions at the time
    • No mechanistic dissection of which targets MED6 directly controls
    • Single knockdown approach without rescue or reciprocal validation

Open questions

Synthesis pass · forward-looking unresolved questions
  • How activator-specific signals are physically integrated at MED6 and converted into the post-recruitment initiation event remains undefined.
  • No structure of an activator-engaged MED6 state
  • The molecular event executed by MED6's essential post-recruitment region is unknown
  • How MED6 bridging dynamics couple to PIC assembly and CTD phosphorylation is unresolved

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 3 GO:0060090 molecular adaptor activity 3 GO:0140110 transcription regulator activity 3
Localization
GO:0005634 nucleus 3 GO:0000228 nuclear chromosome 2
Pathway
R-HSA-1266738 Developmental Biology 3 R-HSA-74160 Gene expression (Transcription) 3 R-HSA-162582 Signal Transduction 2
Partners
MED12MED13MED14MED17MED21MED23MED31MED7
Complex memberships
Mediator complexMediator head moduleRNA polymerase II holoenzyme

Evidence

Reading pass · 21 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1997 Med6 is an essential subunit of the yeast Mediator complex required for transcriptional activation from many class II promoters in vivo; a temperature-sensitive Med6 mutant abolishes inducible transcription without affecting basal or constitutive transcription, and Mediator isolated from this mutant is temperature-sensitive for activation in a reconstituted in vitro system due to a defect in initiation complex formation. Temperature-sensitive mutant analysis, in vivo transcription assays, reconstituted in vitro transcription system Molecular and cellular biology High 9234719
1998 Mouse Mediator contains homologs of yeast Mediator subunits including Med6, binds to the RNA polymerase II C-terminal domain (CTD), and stimulates phosphorylation of the CTD by TFIIH. Biochemical purification, peptide sequencing, CTD binding assay, CTD phosphorylation assay Proceedings of the National Academy of Sciences of the United States of America High 9671713
1998 A functional interaction between Med6 and Srb4 is required for transcriptional activation; an allele-specific dominant suppressor screen identified SRB4 as a suppressor of a med6-ts mutation, and biochemical fractionation showed Med6 and Srb4 co-reside in the same Mediator subcomplex. Genetic suppressor screen, biochemical Mediator subcomplex fractionation, in vivo transcription assays Molecular and cellular biology High 9710620
1998 Human NAT complex, containing the human homolog of Med6 along with Srb7, Srb10, Srb11, and Rgr1, represses activated transcription and phosphorylates the CTD of RNA polymerase II at residues distinct from those phosphorylated by TFIIH; the complex interacts with RNAPII in a CTD-independent manner, and CTD phosphorylation precludes this interaction. Biochemical purification, in vitro transcription repression assay, CTD phosphorylation assay, co-immunoprecipitation with RNAPII Molecular cell High 9734358
1999 Human SMCC complex, containing MED6 along with other SRB/MED homologs, can either repress activator-dependent transcription or, at limiting TFIIH, synergistically enhance it; the complex shows direct activator interactions and can act independently of the RNA polymerase II CTD. Biochemical purification, in vitro transcription assay, activator interaction assay Molecular cell High 10024883
1998 Med6 and Srb6, components of the RNA polymerase II holoenzyme, are dominant suppressors of a temperature-sensitive Srb4 mutation and physically interact with Srb4, placing Med6 within the holoenzyme where it participates in the balance between transcriptional activation and repression. Genetic suppressor screen, physical interaction assay (co-immunoprecipitation), in vivo transcription analysis Molecular and cellular biology Medium 9671455
1999 Med6 is required for all activator-specific transcriptional activation processes tested (Bas1/Bas2-, Gcn4-, Gal4-, Rap1-mediated), whereas other Mediator subunits (Med9/Cse2, Med10/Nut2, Gal11, Med11) show activator-specific requirements; this positions Med6 as a convergence point where diverse activation signals meet to modulate Pol II activity. Differential display, Northern analysis of mRNA from Mediator mutant strains, genetic epistasis Molecular and cellular biology Medium 9891034
2001 Drosophila Med6 (dMed6) is essential for viability and cell proliferation; dMed6 mutants fail to pupate and die in the third larval instar with severe proliferation defects in imaginal discs; cDNA microarray and quantitative RT-PCR show that transcriptional activation of many, but not all, genes is affected, including genes involved in cell proliferation and metabolism. Genetic loss-of-function mutant analysis, cDNA microarray, quantitative RT-PCR, in situ expression analysis Molecular and cellular biology Medium 11438678
2001 C. elegans med-6 is required for development; RNAi of med-6 suppresses gain-of-function phenotypes of Ras pathway components (let-23 and let-60) and enhances loss-of-function of lin-3, placing Med-6 as required for transcriptional output of the Ras signaling pathway; med-6 is also involved in Wnt pathway-dependent male ray development. Genetic mutation analysis, RNAi epistasis with Ras and Wnt pathway alleles, phenotypic readout of signaling pathway outputs Development (Cambridge, England) Medium 11688559
2005 MED7·MED21 (Med7·Srb7) crystal structure at 3.0 Å reveals that MED6 bridges the Mediator middle module to the head module; MED6 binds to putative protein-binding sites on the MED7·MED21 heterodimer surface, and a flexible MED6 bridge together with the MED7·MED21 hinge may account for conformational changes in Mediator upon binding to Pol II or activators. X-ray crystallography (3.0 Å), structural analysis of protein-binding surfaces The Journal of biological chemistry High 15710619
2005 In C. elegans, LET-425/MED6 forms a complex in vivo with LET-19/MED13, DPY-22/MED12, and SUR-2/MED23 (components of the Mediator complex), and this complex is required for Wnt-regulated asymmetric T-cell division and Wnt target gene repression. Co-immunoprecipitation in vivo, lineage analysis of let-19/dpy-22 mutants, epistasis with Wnt pathway components Development (Cambridge, England) Medium 15790964
2006 Med21 interacts with Med6 (confirmed by genetic and 2-hybrid data), and Med21 serves as a molecular switchboard integrating signals within the Mediator middle domain; interactions between Med21 and Med6 suggest Med6 is connected to the middle module through Med21. Two-hybrid analysis, co-immunoprecipitation of tagged proteins in insect cells and E. coli, high-copy suppressor screen Molecular genetics and genomics Medium 16758199
2007 A 600-kDa MED6-containing subcomplex (TMLC3) augments transcriptional activation in vitro but lacks CDK8 and does not phosphorylate RNA Pol II; by contrast, the full 1.5-MDa complex (TMLC1) containing MED6, MED7, and CDK8 both activates transcription and phosphorylates Pol II, and preferentially interacts with TFIIE, TFIIF, and TFIIH. Affinity purification and HPLC-gel filtration of epitope-tagged MED6/MED7/CDK8 complexes, in vitro transcription assay, Pol II phosphorylation assay, co-immunoprecipitation with general transcription factors Genes to cells Medium 17212659
2007 MED28 functions as a negative regulator of smooth muscle cell differentiation in concert with Med6, Med8, and Med18 within the Mediator head module; knockdown and overexpression experiments show Med6-containing head module components act together to suppress smooth muscle cell gene expression. siRNA knockdown, overexpression in NIH3T3 cells, gene expression analysis, mesenchymal precursor transdifferentiation assay The Journal of biological chemistry Low 17848560
2010 MED6 is recruited to the enhancer and proximal promoter of the PPARγ target gene Fabp4 in a MED1-independent manner, as shown by ChIP; MED14 knockdown reduces MED6 occupancy at the Fabp4 proximal promoter without affecting its binding at the enhancer, indicating MED14 is required for functional Mediator recruitment and positioning of MED6 at proximal promoters. ChIP (chromatin immunoprecipitation), siRNA knockdown of MED1 and MED14, reporter and endogenous gene expression assays Molecular and cellular biology Medium 20194623
2012 Crystal structure of the S. pombe Mediator head module at 3.4 Å reveals Med6 as one of seven head module subunits (with Med8, Med11, Med17, Med18, Med20, Med22); Med6 contributes to the fixed jaw submodule and is positioned within the head module architecture that contacts Pol II and its CTD. X-ray crystallography (3.4 Å), structural analysis Nature High 23123849
2014 MED6 knockdown by siRNA significantly impairs HIV-1 replication at a post-integration step by inhibiting early HIV transcripts, specifically affecting transcription of the nascent viral mRNA transactivation-responsive element (TAR); MED6 knockdown also compromises Tat-induced HIV transcription. siRNA knockdown, RT-PCR quantification of HIV transcripts, viral replication assays The Journal of biological chemistry Low 25100719
2017 Crystal structure of 15-subunit core Mediator from S. pombe at 3.4 Å shows that Med6 terminal regions tether the middle module to the head module; sites of known Mediator mutations cluster at the head-middle module interface including Med6 terminal regions; the resulting atomic model of the PIC-cMed complex reveals the hook (containing CTD-crosslinking residues) contacts the TFIIH kinase. X-ray crystallography (3.4 Å), cryo-EM model integration, crosslinking mass spectrometry Nature High 28467824
2018 Postrecruitment function of Med6 in transcriptional activation was demonstrated: a deletion mutant Med6p-Δ6 (amino acids 157-166) allows Mediator recruitment to the lexA operator with TBP but fails to support reporter gene expression, indicating Med6 has an essential role downstream of Mediator recruitment; a Δ2 deletion (amino acids 33-42) destabilizes Med6 and reduces Mediator association. Internal deletion mutagenesis, artificial recruitment assay (LexA fusion), in vitro transcription complementation assay, Western blot, chromatin immunoprecipitation Biochemistry research international Medium 29992056
2023 Cryo-EM/atomic model of yeast PIC-Mediator reveals that the Pol II CTD peptide 1 binds between the Med6 shoulder domain and the Med31 knob domain, defining specific CTD-Mediator contacts; CTD peptide 2 forms additional contacts with Med4. Cryo-EM structural analysis, atomic model building Proceedings of the National Academy of Sciences of the United States of America High 37014863
2023 MED6 silencing by shRNA in cancer cells leads to increased lipid droplet accumulation and upregulation of lipid metabolism marker genes PLIN2 and DGAT1, indicating MED6 transcriptionally suppresses genes involved in lipid droplet biogenesis. RNAi/shRNA knockdown, fluorescence-activated cell sorting for lipid droplets, quantitative gene expression analysis BioFactors (Oxford, England) Low 37983968

Source papers

Stage 0 corpus · 34 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
1998 Mammalian mediator of transcriptional regulation and its possible role as an end-point of signal transduction pathways. Proceedings of the National Academy of Sciences of the United States of America 258 9671713
1999 A novel human SRB/MED-containing cofactor complex, SMCC, involved in transcription regulation. Molecular cell 233 10024883
1998 NAT, a human complex containing Srb polypeptides that functions as a negative regulator of activated transcription. Molecular cell 194 9734358
2017 Core Mediator structure at 3.4 Å extends model of transcription initiation complex. Nature 98 28467824
1998 Interplay of positive and negative regulators in transcription initiation by RNA polymerase II holoenzyme. Molecular and cellular biology 90 9671455
2012 Structure of the Mediator head module. Nature 88 23123849
1999 Activator-specific requirement of yeast mediator proteins for RNA polymerase II transcriptional activation. Molecular and cellular biology 73 9891034
1998 Requirement for a functional interaction between mediator components Med6 and Srb4 in RNA polymerase II transcription. Molecular and cellular biology 71 9710620
2005 Components of the transcriptional Mediator complex are required for asymmetric cell division in C. elegans. Development (Cambridge, England) 70 15790964
2010 MED14 tethers mediator to the N-terminal domain of peroxisome proliferator-activated receptor gamma and is required for full transcriptional activity and adipogenesis. Molecular and cellular biology 67 20194623
1997 A transcriptional mediator protein that is required for activation of many RNA polymerase II promoters and is conserved from yeast to humans. Molecular and cellular biology 67 9234719
2022 Identification of diagnostic genes for both Alzheimer's disease and Metabolic syndrome by the machine learning algorithm. Frontiers in immunology 62 36405716
2005 A conserved mediator hinge revealed in the structure of the MED7.MED21 (Med7.Srb7) heterodimer. The Journal of biological chemistry 62 15710619
2007 A kinase subunit of the human mediator complex, CDK8, positively regulates transcriptional activation. Genes to cells : devoted to molecular & cellular mechanisms 40 17212659
2001 Drosophila Med6 is required for elevated expression of a large but distinct set of developmentally regulated genes. Molecular and cellular biology 29 11438678
2014 Characterization of the influence of mediator complex in HIV-1 transcription. The Journal of biological chemistry 28 25100719
2007 Mediator subunit MED28 (Magicin) is a repressor of smooth muscle cell differentiation. The Journal of biological chemistry 22 17848560
2023 Yeast PIC-Mediator structure with RNA polymerase II C-terminal domain. Proceedings of the National Academy of Sciences of the United States of America 20 37014863
2021 Differential Requirements for Mediator Complex Subunits in Drosophila melanogaster Host Defense Against Fungal and Bacterial Pathogens. Frontiers in immunology 19 33746938
2006 Functional and physical interactions within the middle domain of the yeast mediator. Molecular genetics and genomics : MGG 18 16758199
2024 A kalihinol analog disrupts apicoplast function and vesicular trafficking in P. falciparum malaria. Science (New York, N.Y.) 11 39325875
2001 Biological significance of a universally conserved transcription mediator in metazoan developmental signaling pathways. Development (Cambridge, England) 11 11688559
2021 A large-scale genome-wide association analysis reveals QTL and candidate genes for intramuscular fat content in Duroc pigs. Animal genetics 10 34060118
2001 The MED-7 transcriptional mediator encoded by let-49 is required for gonad and germ cell development in Caenorhabditis elegans. FEBS letters 10 11728440
1999 GABAergic and non-GABAergic spiking interneurons of local and intersegmental groups in the crayfish terminal abdominal ganglion. The Journal of comparative neurology 10 10398056
2012 [Study on gene differential expressions of substance and energy metabolism in chronic superficial gastritis patients of Pi deficiency syndrome and of pi-wei hygropyrexia syndrome]. Zhongguo Zhong xi yi jie he za zhi Zhongguo Zhongxiyi jiehe zazhi = Chinese journal of integrated traditional and Western medicine 8 23185754
2023 Regulation of fungal raw-starch-degrading enzyme production depends on transcription factor phosphorylation and recruitment of the Mediator complex. Communications biology 4 37828083
2018 Postrecruitment Function of Yeast Med6 Protein during the Transcriptional Activation by Mediator Complex. Biochemistry research international 4 29992056
2021 ABCB1 inhibition provides a novel therapeutic target to block TWIST1-induced migration in medulloblastoma. Neuro-oncology advances 3 33948561
2021 Genetic interaction between RLM1 and F-box motif encoding gene SAF1 contributes to stress response in Saccharomyces cerevisiae. Genes and environment : the official journal of the Japanese Environmental Mutagen Society 2 34627408
2025 Anterior-posterior patterning in the chaetognath Spadella cephaloptera informs bilaterian nervous system and tail evolution. Communications biology 1 41454138
2023 A new strategy for screening novel functional genes involved in reduction of lipid droplet accumulation. BioFactors (Oxford, England) 1 37983968
2023 A Potent Kalihinol Analogue Disrupts Apicoplast Function and Vesicular Trafficking in P. falciparum Malaria. bioRxiv : the preprint server for biology 1 38045341
2026 PsAvh109 suppresses SA-triggered immunity by mimicking TPL function to disrupt mediator complex assembly. Nature communications 0 41986337

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