{"gene":"GTF2B","run_date":"2026-04-28T18:06:53","timeline":{"discoveries":[{"year":1991,"finding":"TFIIB directly binds the acidic activating region of VP16 protein without requiring additional adaptor proteins, establishing TFIIB as a direct target of acidic activators and a rate-limiting step in preinitiation complex assembly.","method":"Affinity chromatography with recombinant bacterially expressed TFIIB; in vitro binding assays","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1-2 — recombinant protein binding assay demonstrating direct interaction, replicated across multiple labs","pmids":["1922364"],"is_preprint":false},{"year":1991,"finding":"TFIIB contains a region with amino acid sequence similarity to bacterial sigma factors, consistent with an analogous role in promoter recognition; it also contains a large imperfect repeat and clusters of basic residues, suggesting it serves as a bridge between TFIID and RNA polymerase II during preinitiation complex assembly.","method":"cDNA cloning, sequencing, sequence homology analysis, purification to homogeneity","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 — original cloning and purification paper with functional characterization, widely cited foundational work","pmids":["1946368"],"is_preprint":false},{"year":1992,"finding":"S300-II (TFIIB) directly interacts with members of the steroid hormone receptor superfamily (COUP-TF, estrogen receptor, progesterone receptor) via protein-protein interactions, independent of adaptor proteins, identifying TFIIB as a direct target of nuclear receptor transactivators.","method":"Recombinant protein-protein interaction assays with purified proteins","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — direct binding with recombinant proteins, replicated with multiple receptor family members","pmids":["1517211"],"is_preprint":false},{"year":1992,"finding":"The yeast SUA7 gene encodes a TFIIB homolog that is required for normal transcription start site selection in vivo; sua7 mutations cause downstream shifts in transcription initiation at multiple loci (cyc1, ADH1), establishing TFIIB's role in start site selection.","method":"Genetic suppressor screen, molecular cloning, primer extension analysis of transcripts","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 — genetic and molecular analysis in yeast model organism, replicated at multiple loci","pmids":["1547497"],"is_preprint":false},{"year":1993,"finding":"TFIIB consists of two separable functional domains: the C-terminal core domain (TFIIBc) interacts with TBP-DNA complex, while the N-terminal domain is required for recruitment of RNA polymerase II-TFIIF into the initiation complex. Mutagenesis of cysteine residues in the N-terminal zinc finger blocks Pol II-TFIIF recruitment without impairing TBP binding.","method":"Limited proteolysis domain mapping; mutagenesis of cysteine codons; gel mobility-shift assays; in vitro transcription assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — multiple orthogonal methods (proteolysis, mutagenesis, in vitro transcription), replicated across labs","pmids":["8516312","8515820","8516311"],"is_preprint":false},{"year":1993,"finding":"Drosophila TAFII40 directly binds both the VP16 activation domain and TFIIB, suggesting a ternary interaction among activator, coactivator, and TFIIB. Antibodies against dTAFII40 inhibit GAL4-VP16 activation without affecting basal transcription.","method":"In vitro protein-protein interaction assays; affinity chromatography; antibody inhibition","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 — direct binding assays with multiple orthogonal methods, functional antibody inhibition","pmids":["8221891"],"is_preprint":false},{"year":1993,"finding":"HSV ICP4 forms a tripartite complex with TFIIB and TBP/TFIID on promoter DNA containing TATA box and ICP4-binding site; protein-protein interactions among all three proteins increase the affinity of ICP4 and TBP for their respective binding sites.","method":"Gel retardation assays, DNase I footprinting, use of mutant ICP4 derivatives","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 2 — multiple biochemical methods with mutant analysis","pmids":["8392607"],"is_preprint":false},{"year":1993,"finding":"TFIIB core (C-terminal domain) forms a compact, protease-resistant structure that retains TBP binding but cannot support transcription. The N-terminal region mediates direct interaction with RNA Pol II (in association with TFIIF), and RNA Pol II may induce a conformational change in TFIIB leading to cryptic DNA-binding activity.","method":"Limited proteolysis, in vitro transcription, gel mobility-shift, DNase I footprinting","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple biochemical methods, conformational model validated by protease sensitivity","pmids":["8413225"],"is_preprint":false},{"year":1994,"finding":"Specific TFIIB mutations (sua7-1: E62K; sua7-2: E62K; sua7-3: R78C) define conserved residues adjacent to the zinc finger of TFIIB as critical determinants of transcription start site selection. Double-mutant analysis suggests an E62-R78 salt bridge as an important structural element in this domain.","method":"Site-directed mutagenesis, reciprocal charge-swap double mutants, in vivo suppressor analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — comprehensive mutagenesis with reciprocal charge swaps and in vivo phenotype validation","pmids":["7982976"],"is_preprint":false},{"year":1994,"finding":"SUA8 mutations in the largest subunit of RNA polymerase II (RPB1) cause downstream shifts in transcription start site selection similar to sua7 (TFIIB) mutations; sua7 sua8 double mutants show synthetic lethality and non-allelic non-complementation, establishing a functional interaction between TFIIB and RPB1 in start site selection.","method":"Genetic suppressor screen, molecular cloning, synthetic lethality analysis, transcript mapping","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with multiple alleles and synthetic lethality","pmids":["8264591"],"is_preprint":false},{"year":1994,"finding":"The proline-rich activation domain of CTF1 selectively interacts with TFIIB (but not TBP) and facilitates TFIIB recruitment to TBP-DNA complexes, demonstrating that different activator types can target TFIIB for preinitiation complex assembly.","method":"In vitro protein-protein interaction; gel retardation assays monitoring TFIIB recruitment","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — direct binding plus functional recruitment assay in both human and yeast systems","pmids":["8183887"],"is_preprint":false},{"year":1995,"finding":"Crystal structure of the TFIIB/TBP/TATA-element ternary complex at 2.7 Å reveals that core TFIIB resembles cyclin A and recognizes the preformed TBP-DNA complex through protein-protein and protein-DNA interactions; the N-terminal domain of core TFIIB forms the downstream surface of the ternary complex, potentially fixing the transcription start site.","method":"X-ray crystallography at 2.7 Å resolution","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure of the ternary complex, foundational structural paper","pmids":["7675079"],"is_preprint":false},{"year":1995,"finding":"NMR structure of human TFIIB core domain (TFIIBc) reveals two direct repeats with similar alpha-helical folds (resembling cyclin A) conferring pseudo-twofold symmetry; an extensive central basic surface including an amphipathic alpha helix is critical for TFIIB function as a bridge between TBP-promoter complex and RNA Pol II.","method":"Multidimensional heteronuclear NMR spectroscopy","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 — NMR structure with functional validation of identified surface residues","pmids":["7671313"],"is_preprint":false},{"year":1995,"finding":"Monomeric Drosophila Krüppel (Kr) activates transcription through interaction with TFIIB when acting near the basal promoter, whereas Kr dimers repress transcription through interaction with TFIIE beta.","method":"In vitro protein-protein interaction assays, in vitro transcription with purified factors","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — direct protein interaction assays with functional transcription readout distinguishing activator vs. repressor modes","pmids":["7753175"],"is_preprint":false},{"year":1995,"finding":"VDR (vitamin D receptor) directly binds TFIIB via select protein domains; co-transfection of VDR and TFIIB cooperatively activates a 1,25(OH)2D3-responsive reporter in a ligand-dependent manner in P19 cells, demonstrating functional interaction between TFIIB and a nuclear hormone receptor in vivo.","method":"GST fusion protein-protein binding assays; cotransfection reporter assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — direct binding assay plus in vivo functional confirmation by cotransfection","pmids":["7878015"],"is_preprint":false},{"year":1995,"finding":"Hydroxyl-radical footprinting and gel mobility-shift assays reveal that TFIIB binds beneath the concave surface of TBP, contacting DNA both upstream and downstream of the TATA box; TFIIB requires at least 7 bp of DNA on either side of the TATA box to form a stable TFIIB-TBP-DNA complex.","method":"Gel mobility-shift assays, hydroxyl-radical footprinting mapped onto TBP-DNA crystal structure","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — orthogonal biochemical methods with structural interpretation","pmids":["7637813"],"is_preprint":false},{"year":1995,"finding":"High-resolution protein-DNA photocrosslinking reveals TFIIA and TFIIB make more extensive interactions with promoter DNA than previously anticipated; TBP, TFIIA, and TFIIB together surround promoter DNA for two turns of the helix, forming a 'cylindrical clamp' effectively topologically linked to promoter DNA.","method":"Site-specific protein-DNA photocrosslinking in binary, ternary, and quaternary complexes","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — novel photocrosslinking approach with systematic mapping","pmids":["8855228"],"is_preprint":false},{"year":1995,"finding":"The N-terminal A/B domain (amino acids 21-30, containing a basic amino acid cluster) of thyroid hormone receptor alpha (T3Rα) is essential for transcriptional activation and directly interacts with TFIIB (residues 178-201); this interaction is required for T3Rα-mediated transcriptional activation.","method":"In vitro binding studies with recombinant proteins; deletion and mutagenesis analysis; transient transfection","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — domain mapping by mutagenesis with direct binding assays and in vivo functional validation","pmids":["7623841"],"is_preprint":false},{"year":1995,"finding":"Protease footprinting reveals two regions of TFIIB protected by the VP16 activation domain and one region protected by TAFII40 (overlapping with the VP16 site), defining a regulatory surface on TFIIB that serves as an interface for both activators and coactivators.","method":"Protease footprinting with broad-specificity proteases on 32P-labeled TFIIB","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — novel methodology directly visualizing binding surfaces on TFIIB","pmids":["7597078"],"is_preprint":false},{"year":1995,"finding":"Diverse activators (acidic, proline-rich, glutamine-rich) fail to recruit mutant forms of TFIIB that cannot respond to activators, demonstrating that activator-mediated TFIIB recruitment is a central and universal step in transcriptional activation; TFIIB dissociates after each round of transcription, requiring reassembly for each reinitiation.","method":"In vitro transcription with TFIIB mutants; gel retardation assays for TFIIB recruitment","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 2 — multiple activator classes tested, reinitiation mechanism demonstrated biochemically","pmids":["7583100"],"is_preprint":false},{"year":1996,"finding":"RAP74 (large subunit of TFIIF) directly binds TFIIB through its C-terminal region, while RAP30 binds TFIIB at an overlapping region; RAP74 blocks TFIIB-RAP30 binding by simultaneously binding TFIIB and RAP30, indicating that when TFIIF is intact, TFIIB-TFIIF contact is maintained through RAP74.","method":"Deletion mutagenesis, in vitro binding assays, in vitro transcription","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — domain mapping with direct binding assays and functional transcription data","pmids":["8662660"],"is_preprint":false},{"year":1996,"finding":"IRF-1 and IRF-2 bind to TFIIB; IRF-1 and TFIIB cooperatively enhance ISRE promoter activity both in vitro and in vivo; this cooperation is independent of the TATA sequence but dependent on the initiator sequence (Inr) and is cell-type specific.","method":"In vitro protein binding assays; in vitro transcription; cotransfection reporter assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — direct binding plus orthogonal in vitro and in vivo functional data","pmids":["8887661"],"is_preprint":false},{"year":1996,"finding":"The yeast SUB1 protein (homolog of human co-activator PC4) binds TFIIB in vitro and specifically inhibits TBP-TFIIB-promoter complex formation; overexpression of SUB1 suppresses TFIIB alleles E62G and R78H, suggesting SUB1 facilitates TFIIB release during transcription initiation.","method":"Genetic suppressor screen; in vitro binding assays; gel retardation for complex formation","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis combined with direct biochemical binding and complex formation assays","pmids":["8617240"],"is_preprint":false},{"year":1998,"finding":"TFIIB directly interacts with HBV pX protein in vivo (co-immunoprecipitation from nuclear extracts); pX bridges an otherwise inefficient TFIIB-POLII interaction, using TFIIB as a molecular scaffold for transcriptional coactivation.","method":"Co-immunoprecipitation from nuclear extracts; TFIIB mutant analysis; in vitro and in vivo transcription assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — co-IP from nuclear extracts combined with mutant TFIIB functional dissection in vivo and in vitro","pmids":["9488473"],"is_preprint":false},{"year":1998,"finding":"TFIIB mediates sequence-specific DNA binding by recognizing a defined element upstream of the TATA box (BRE), and this recognition cooperates with TBP-TATA binding as a codeterminant of promoter strength.","method":"Mutagenesis, in vitro binding assays, in vitro transcription","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1-2 — direct demonstration of sequence-specific DNA binding by TFIIB with functional consequences","pmids":["9660923"],"is_preprint":false},{"year":1998,"finding":"The N-terminal region of yeast TFIIB contains two separable adjacent functional domains: the zinc ribbon fold mediates stable RNA Pol II binding, while a highly conserved homology block C-terminal to the zinc ribbon controls transcription start site selection.","method":"Site-directed mutagenesis; in vitro transcription; start site selection assays in vitro and in vivo; pulldown assays with purified Pol II","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — systematic mutagenesis with multiple orthogonal functional assays","pmids":["9651390"],"is_preprint":false},{"year":1998,"finding":"NMR analysis shows TFIIB core domain is conformationally flexible in solution; binding of the VP16 activation domain or the N-terminal zinc domain induces chemical shift changes in the first repeat and interrepeat linker of TFIIBc, suggesting TFIIB is pliable and can be modulated by activator interactions to prime binding to TBP-DNA complexes.","method":"1H-15N NMR, backbone 15N relaxation measurements, comparison with crystal structure","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — NMR solution structure with dynamics analysis and direct activator interaction mapping","pmids":["9609687"],"is_preprint":false},{"year":1999,"finding":"Genetic epistasis in yeast establishes functional interactions among TFIIB, Ssu72, and Sub1 that are allele-specific and linked specifically to TFIIB alleles affecting transcription start site selection, placing Ssu72 and Sub1 in the same functional pathway as TFIIB for start site selection.","method":"Error-prone PCR mutagenesis library, genetic suppressor/enhancer analysis, allele-specificity testing","journal":"Genetics","confidence":"High","confidence_rationale":"Tier 2 — comprehensive allele-specific epistasis analysis","pmids":["10511545"],"is_preprint":false},{"year":1999,"finding":"The TFIIB S53P mutation specifically impairs activation of PHO5 and ADH2 without affecting basal transcription; Pho4 directly interacts with TFIIB in vitro and induces a conformational change in TFIIB (detected by enhanced V8 protease sensitivity), suggesting certain activators function by inducing conformational changes in TFIIB.","method":"Yeast mutagenesis screen; in vitro binding assay; protease sensitivity assay; reporter gene analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — combined genetic and biochemical approaches demonstrating conformational change","pmids":["10077585"],"is_preprint":false},{"year":2000,"finding":"Fcp1p (CTD phosphatase) directly binds the first cyclin-like repeat in the TFIIB core domain via a KEFGK motif shared by TFIIB and the RAP74 subunit of TFIIF; this interaction is functionally significant for transcriptional activation.","method":"Deletion/point mutagenesis of Fcp1p; direct binding assays; genetic synthetic phenotype analysis","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — domain mapping by mutagenesis combined with direct binding and genetic interaction data","pmids":["11003641"],"is_preprint":false},{"year":2001,"finding":"The BRE (TFIIB recognition element) upstream of the TATA box suppresses basal transcription, and activator proteins can disrupt the TFIIB-BRE interaction within promoter-bound complexes, revealing a novel activator function in modulating core promoter recognition by TFIIB.","method":"In vitro transcription assays; protein-DNA interaction assays","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 — functional dissection with clear mechanistic interpretation","pmids":["11711430"],"is_preprint":false},{"year":2004,"finding":"Crystal structure of RNA Pol II-TFIIB cocrystal at 4.5 Å reveals three functional features: the TFIIB zinc ribbon domain contacts the Pol II dock domain near the RNA exit path; the B-finger domain inserts into the Pol II active center; and the C-terminal domain orients promoter DNA for unwinding and transcription initiation.","method":"X-ray crystallography at 4.5 Å","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — high-resolution cocrystal structure revealing direct mechanism of Pol II-TFIIB interaction","pmids":["14963322"],"is_preprint":false},{"year":2003,"finding":"Site-specific photocrosslinking and directed hydroxyl radical probing map the TFIIB zinc ribbon domain to the Pol II Dock domain surface overlapping the RNA exit point within the preinitiation complex, defining a general mechanism for TFIIB-like factor interaction with RNA polymerases.","method":"Site-specific photocrosslinking, directed hydroxyl radical probing, mutational analysis","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 — multiple direct mapping approaches with mutagenesis validation","pmids":["14536083"],"is_preprint":false},{"year":2004,"finding":"Biochemical probes on TFIIB reveal that in full PICs (not in the smaller Pol II-TFIIB complex), TFIIB linker and core domains are positioned over the central cleft and wall of Pol II; TFIIF subunit Tfg1 is in close proximity to TFIIB B-finger, linker, and core domains, suggesting close cooperation between TFIIB and TFIIF during initiation.","method":"Site-specific chemical probing of TFIIB within the PIC","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 — systematic biochemical mapping across the full PIC","pmids":["15479635"],"is_preprint":false},{"year":2004,"finding":"Functional interaction between TFIIB and the Rpb2 subunit of RNA Pol II is established by suppressor genetics; the B-finger domain (R78C) of TFIIB functionally interacts with the lobe domain (G369S) of Rpb2 in start site selection; TFIIB R78C alters abortive initiation patterns without precluding initiation.","method":"Genetic suppressor screen; in vitro transcription; run-on transcription; abortive initiation assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis combined with multiple biochemical transcription assays","pmids":["15082791"],"is_preprint":false},{"year":2005,"finding":"TFIIB defines a downstream core promoter element (BREd, distinct from the upstream BRE); two independent DNA-binding motifs in TFIIB recognize elements flanking the TATA box and cooperate in transcription regulation in a promoter context-dependent manner.","method":"In vitro transcription assays; protein-DNA binding assays; mutagenesis","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 — functional dissection with clear definition of two independent DNA-binding domains","pmids":["16230532"],"is_preprint":false},{"year":2005,"finding":"Regardless of TATA-to-start-site spacing, the upstream transcription bubble edge forms 20 bp from TATA; the B-finger of TFIIB causes pausing at +7 to +9 within the complex, and bubble collapse (reannealing of upstream ~8 bases when bubble reaches 18 bp and RNA is ≥7 nt) suppresses this pausing and marks the promoter clearance transition.","method":"In vitro transcription with systematically varied promoter spacing; bubble mapping; nucleotide depletion","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1-2 — systematic in vitro dissection of bubble dynamics and TFIIB B-finger role in clearance","pmids":["15989968"],"is_preprint":false},{"year":2007,"finding":"TFIIB has a transcription-independent role in gene looping in yeast: TFIIB crosslinks to both promoter and terminator regions of genes; the E62K TFIIB mutation adversely affects looping at multiple genes; TFIIB association with the terminator is dependent on the Ssu72 component of the CPF 3' end processing complex and is independent of TBP.","method":"Chromatin immunoprecipitation (ChIP); chromosome conformation capture (3C); genetic analysis with TFIIB and Ssu72 mutants","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (ChIP, 3C) with genetic validation","pmids":["17803944"],"is_preprint":false},{"year":2007,"finding":"Expansion of the polyglutamine tract in TBP (SCA17) enhances the TBP-TFIIB interaction while reducing TBP dimerization; this leads to decreased TFIIB occupancy of the Hspb1 promoter and downregulation of HSPB1 in SCA17 transgenic mice; overexpression of TFIIB alleviates mutant TBP-induced neuritic defects.","method":"Transgenic mouse model; co-immunoprecipitation; ChIP; neuritic defect rescue","journal":"Nature neuroscience","confidence":"High","confidence_rationale":"Tier 2 — in vivo mouse model with multiple biochemical methods and functional rescue","pmids":["17994014"],"is_preprint":false},{"year":2009,"finding":"Crystal structure of the complete Pol II-TFIIB complex at 4.3 Å reveals initiation mechanism: B-core domain binds Pol II wall to position promoter DNA over the active centre cleft; B-linker binds the Pol II rudder and clamp coiled-coil to assist DNA opening; B-reader approaches the active site to assist template strand scanning and TSS recognition; RNA synthesis and DNA rewinding displace B-reader and B-linker to trigger TFIIB release and elongation.","method":"X-ray crystallography at 4.3 Å; complementary functional mutagenesis data","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure with complementary functional validation","pmids":["19820686"],"is_preprint":false},{"year":2009,"finding":"A 3.8 Å crystal structure of the Pol II-TFIIB complex reveals the C-terminal region of TFIIB positioned above the polymerase active center cleft, and the linker between N- and C-terminal regions snaking down toward the active center; together with the prior 4.5 Å structure, these define two distinct conformational states of TFIIB in the complex.","method":"X-ray crystallography at 3.8 Å","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — complementary crystal structure clarifying TFIIB domain positioning","pmids":["19965383"],"is_preprint":false},{"year":2010,"finding":"TFIIB is phosphorylated at serine 65 in vivo within preinitiation complexes; this phosphorylation occurs after RNA Pol II CTD serine 5 phosphorylation but before productive initiation; phospho-S65 TFIIB regulates interaction with CstF-64 (component of the CstF cleavage/polyadenylation complex), directing CstF recruitment to the terminator and linking promoter to terminator function.","method":"In vivo phosphorylation mapping; PIC assembly analysis; ChIP; co-immunoprecipitation with CstF-64","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods identifying the modification, its writer order, and functional consequence","pmids":["20226668"],"is_preprint":false},{"year":2011,"finding":"TFIIF is not required for RNA Pol II initiation or promoter clearance per se, but is essential for stabilizing TFIIB in early elongation complexes; without TFIIF, TFIIB can be lost immediately after initiation rather than at the normal +12 to +13 displacement point.","method":"Casein kinase 2 phosphorylation of TFIIF to generate TFIIF-depleted PICs; in vitro transcription; factor retention analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — mechanistic dissection of factor requirements with controlled biochemical system","pmids":["21896726"],"is_preprint":false},{"year":2012,"finding":"Crystal structures of the Pol II-TFIIB complex at 3.4 Å and of an initially transcribing complex (with DNA template and 6-nt RNA) reveal: the complete B-reader does not reach the active site but binds DNA template strand upstream to assist initiator recognition and TSS positioning; TFIIB rearranges active-site residues and induces metal B binding; TFIIB prevents tilting of the DNA-RNA hybrid; when RNA grows beyond 6 nt, the B-reader loop directs RNA to its exit tunnel; when RNA reaches 12-13 nt, it clashes with TFIIB, triggering TFIIB displacement and elongation complex formation.","method":"X-ray crystallography at 3.4 Å; initially transcribing complex structure; functional mutagenesis","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structures of multiple complexes with functional validation","pmids":["23151482"],"is_preprint":false},{"year":2016,"finding":"Single-molecule analysis reveals TFIIB binding to the promoter is highly transient (average residence time ~1.5 sec) when TFIID and TFIIA are present, but undergoes a transient-to-stable transition only in the presence of Pol II-TFIIF, establishing Pol II-TFIIF recruitment as a checkpoint for TFIIB stabilization in PIC assembly.","method":"Single-molecule fluorescence microscopy; live-cell imaging; in vitro reconstituted transcription system","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 — novel single-molecule approach revealing dynamics invisible to ensemble methods, validated by live-cell imaging","pmids":["27798851"],"is_preprint":false},{"year":2016,"finding":"Mediator interacts with TFIIB through its middle module subunit Med10; this Mediator-TFIIB interaction has a global role in PIC assembly genome-wide, and the amplitude of Mediator's effect on PIC formation is dependent on promoter architecture (TATA elements, nucleosome occupancy).","method":"In vivo ChIP, in vitro PIC assembly assays, genome-wide analysis, Med10 mutant analysis","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal approaches (in vivo, in vitro, genome-wide) identifying specific interaction domain","pmids":["27688401"],"is_preprint":false},{"year":2022,"finding":"Rapid acute depletion of TFIIB in HAP1 cells shows the largest general effect on RNA Pol II promoter activity among GTFs tested; TFIIB depletion also correlates with apparent transcription termination defects downstream of genes, consistent with its role in linking initiation and termination.","method":"Rapid auxin-induced depletion; precision nuclear run-on sequencing (PRO-Seq) genome-wide","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 — genome-wide functional measurement with acute depletion across >70,000 promoters","pmids":["35947745"],"is_preprint":false}],"current_model":"TFIIB (GTF2B) is a general transcription factor that bridges promoter-bound TFIID/TBP and RNA Polymerase II during preinitiation complex (PIC) assembly: its C-terminal cyclin-fold core domain recognizes TBP and flanking promoter DNA elements (BREu upstream and BREd downstream of the TATA box), while its N-terminal zinc ribbon domain contacts the Pol II dock domain to recruit Pol II; upon PIC formation, the B-linker assists DNA opening and the B-reader positions the template strand for transcription start site selection; after synthesis of ~12-13 nt RNA, the growing transcript clashes with TFIIB, triggering its displacement to allow elongation complex formation; TFIIB is also phosphorylated at Ser65 within the PIC, linking initiation to 3' end processing/termination machinery (CstF), and has a transcription-independent role in gene loop formation between promoters and terminators."},"narrative":{"teleology":[{"year":1991,"claim":"Cloning and purification of TFIIB revealed it as a single-polypeptide general transcription factor with structural homology to bacterial sigma factors and direct repeat architecture, establishing it as a bridge between TFIID and RNA Pol II, and identifying it as a direct target of acidic activators like VP16.","evidence":"cDNA cloning, sequence analysis, recombinant protein affinity chromatography with VP16","pmids":["1946368","1922364"],"confidence":"High","gaps":["No structural model of TFIIB at this stage","Mechanism of how activator binding stimulates PIC assembly unknown"]},{"year":1992,"claim":"Yeast genetics showed that TFIIB (SUA7) is a determinant of transcription start site selection in vivo, shifting the understanding of TFIIB from a passive scaffold to an active participant in positioning the initiation site.","evidence":"Genetic suppressor screen at cyc1 and ADH1 loci; primer extension mapping of start sites in sua7 mutants","pmids":["1547497"],"confidence":"High","gaps":["Structural basis of start site selection unknown","Whether mammalian TFIIB performs the same function unclear"]},{"year":1993,"claim":"Domain dissection established that TFIIB has a bipartite architecture: the C-terminal core binds TBP–DNA while the N-terminal zinc-finger region recruits RNA Pol II–TFIIF, resolving how one factor bridges promoter recognition and polymerase recruitment.","evidence":"Limited proteolysis, cysteine mutagenesis, gel-shift and in vitro transcription assays","pmids":["8516312","8515820","8413225"],"confidence":"High","gaps":["Atomic resolution structure lacking","Role of the linker between domains unknown"]},{"year":1995,"claim":"Crystal and NMR structures of the TFIIB core domain and the TFIIB–TBP–TATA ternary complex revealed the cyclin-fold architecture and how TFIIB contacts DNA both upstream and downstream of the TATA box, providing the first atomic framework for understanding promoter recognition and start site positioning.","evidence":"X-ray crystallography at 2.7 Å; multidimensional NMR spectroscopy; hydroxyl-radical footprinting","pmids":["7675079","7671313","7637813"],"confidence":"High","gaps":["Structure of TFIIB with Pol II not yet determined","BRE sequence specificity not formally defined"]},{"year":1995,"claim":"TFIIB was shown to be a convergent target of diverse activator classes (acidic, proline-rich, glutamine-rich) and nuclear receptors, with activator binding inducing conformational changes on a defined regulatory surface, establishing TFIIB recruitment as a universal rate-limiting step in transcriptional activation.","evidence":"In vitro transcription with TFIIB mutants; protease footprinting; protein-protein binding with VDR, T3Rα, CTF1, VP16","pmids":["7583100","7597078","7878015","8183887"],"confidence":"High","gaps":["Structural basis of activator-induced conformational change unresolved","Whether all promoters depend equally on TFIIB recruitment unknown"]},{"year":1998,"claim":"TFIIB was found to recognize a specific upstream DNA element (BRE) as a codeterminant of promoter strength, and the N-terminal zinc ribbon and adjacent B-finger were shown to have separable functions in Pol II binding versus start site selection, refining the functional map of TFIIB's N-terminal region.","evidence":"In vitro binding and transcription with promoter and TFIIB mutants; yeast mutagenesis","pmids":["9660923","9651390"],"confidence":"High","gaps":["Downstream BRE not yet identified","Mechanism of B-finger action in start site selection unknown at atomic level"]},{"year":2004,"claim":"The first crystal structure of the Pol II–TFIIB complex revealed three key contacts: the zinc ribbon at the Pol II dock domain, the B-finger inserted into the active center, and the C-terminal domain orienting promoter DNA, providing a structural explanation for TFIIB's multifunctional role in initiation.","evidence":"X-ray crystallography at 4.5 Å; site-specific photocrosslinking; directed hydroxyl radical probing","pmids":["14963322","14536083"],"confidence":"High","gaps":["Resolution insufficient to define B-reader contacts with template strand","Initially transcribing complex structure lacking"]},{"year":2005,"claim":"A downstream BRE (BREd) was identified, showing TFIIB recognizes elements flanking both sides of the TATA box through two independent DNA-binding motifs, and the B-finger was shown to cause pausing at +7–9, with bubble collapse marking the promoter clearance transition.","evidence":"In vitro transcription with varied promoter spacing; bubble mapping; BREd mutagenesis","pmids":["16230532","15989968"],"confidence":"High","gaps":["How BREu and BREd cooperate structurally in the full PIC unclear","Whether bubble collapse is the sole trigger for TFIIB release unknown"]},{"year":2007,"claim":"TFIIB was found to occupy both promoter and terminator regions of genes and to be required for gene loop formation in an Ssu72-dependent manner, revealing a transcription-independent structural role that physically links initiation and termination.","evidence":"ChIP and chromosome conformation capture (3C) in yeast with TFIIB and Ssu72 mutants","pmids":["17803944"],"confidence":"High","gaps":["Whether gene looping occurs in mammalian cells via TFIIB unknown","Molecular contacts at the terminator not defined"]},{"year":2009,"claim":"Higher-resolution Pol II–TFIIB crystal structures resolved the complete mechanism: B-linker assists DNA opening by binding the Pol II rudder, B-reader assists template scanning and TSS recognition, and RNA synthesis plus DNA rewinding displace B-reader/B-linker to trigger TFIIB release.","evidence":"X-ray crystallography at 4.3 Å and 3.8 Å with functional mutagenesis","pmids":["19820686","19965383"],"confidence":"High","gaps":["Structure of an actively transcribing complex with nascent RNA still needed","Role of TFIIF in stabilizing TFIIB during this process not structurally resolved"]},{"year":2010,"claim":"Phosphorylation of TFIIB at Ser65 within the PIC was shown to regulate interaction with CstF-64, directing 3′-end processing machinery recruitment and providing a molecular mechanism linking promoter-bound TFIIB to termination.","evidence":"In vivo phosphorylation mapping; ChIP; co-immunoprecipitation with CstF-64","pmids":["20226668"],"confidence":"High","gaps":["Kinase responsible for Ser65 phosphorylation not identified","Whether this modification is universal across all Pol II genes unknown"]},{"year":2012,"claim":"Crystal structures of the initially transcribing complex revealed that the B-reader binds template strand upstream of the active site for TSS positioning, directs RNA to the exit tunnel after 6 nt, and is displaced by clash with the growing RNA at 12–13 nt, completing the structural narrative of TFIIB function from initiation through clearance.","evidence":"X-ray crystallography at 3.4 Å of Pol II–TFIIB with DNA template and 6-nt RNA; mutagenesis","pmids":["23151482"],"confidence":"High","gaps":["Full PIC structure with all GTFs not yet available at this resolution","Dynamics of TFIIB displacement in vivo not directly measured"]},{"year":2016,"claim":"Single-molecule and genome-wide studies showed that TFIIB promoter binding is highly transient (~1.5 s) until stabilized by Pol II–TFIIF arrival, and that Mediator contacts TFIIB through Med10 to facilitate PIC assembly genome-wide in a promoter architecture-dependent manner.","evidence":"Single-molecule fluorescence microscopy; ChIP genome-wide; Med10 mutant analysis in vitro and in vivo","pmids":["27798851","27688401"],"confidence":"High","gaps":["How Mediator–TFIIB interaction is regulated at individual promoters unclear","Structural basis of Med10–TFIIB contact unknown"]},{"year":2022,"claim":"Acute TFIIB depletion showed it has the largest effect on Pol II promoter activity among general transcription factors and confirmed termination defects downstream of genes, validating TFIIB's dual role in initiation and termination genome-wide in human cells.","evidence":"Auxin-induced degradation in HAP1 cells; PRO-seq genome-wide","pmids":["35947745"],"confidence":"High","gaps":["Whether termination defects are direct consequences of lost gene looping or lost CstF recruitment not resolved","Promoter-specific dependencies on TFIIB not fully characterized"]},{"year":null,"claim":"Key unresolved questions include the identity of the Ser65 kinase, the structural basis of gene loop formation at terminators, whether TFIIB displacement dynamics differ across promoter classes in vivo, and how Mediator–TFIIB and activator–TFIIB interactions are coordinated within the complete PIC.","evidence":"","pmids":[],"confidence":"High","gaps":["Ser65 kinase identity unknown","Structural basis of TFIIB at terminators not determined","Complete human PIC structure with TFIIB at atomic resolution not available","In vivo single-molecule dynamics of TFIIB displacement during elongation transition not measured"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[11,15,24,35]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[1,3,4,11,39,46]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[4,7,31,39]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[37,41,46]},{"term_id":"GO:0005654","term_label":"nucleoplasm","supporting_discovery_ids":[33,41,44]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[1,3,4,11,31,39,43,46]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[41,37,46]}],"complexes":["RNA Polymerase II preinitiation complex (PIC)"],"partners":["TBP","RPB1","RPB2","RAP74","RAP30","CSTF2","SSU72","MED10"],"other_free_text":[]},"mechanistic_narrative":"GTF2B (TFIIB) is a general transcription factor essential for RNA polymerase II preinitiation complex (PIC) assembly, transcription start site selection, promoter clearance, and coupling of initiation to termination. Its C-terminal cyclin-fold core domain recognizes TBP on promoter DNA and contacts flanking BRE elements upstream and downstream of the TATA box, while its N-terminal zinc ribbon domain binds the Pol II dock domain to recruit Pol II–TFIIF; within the PIC, the B-linker assists DNA strand opening and the B-reader positions the template strand for start site selection, with TFIIB displacement triggered by clash with the growing RNA transcript at 12–13 nucleotides to permit elongation [PMID:19820686, PMID:23151482, PMID:9660923, PMID:16230532]. TFIIB is a direct target of diverse transcriptional activators—including acidic (VP16), proline-rich (CTF1), and nuclear receptor classes—whose binding induces conformational changes that modulate TFIIB recruitment and PIC formation [PMID:1922364, PMID:1517211, PMID:10077585, PMID:7583100]. Beyond initiation, TFIIB is phosphorylated at Ser65 within the PIC, linking it to CstF-mediated 3′-end processing, and participates in gene loop formation between promoters and terminators via interaction with the Ssu72 phosphatase, establishing TFIIB as a physical and functional bridge coupling transcription initiation to termination [PMID:20226668, PMID:17803944, PMID:35947745]."},"prefetch_data":{"uniprot":{"accession":"Q00403","full_name":"Transcription initiation factor IIB","aliases":["General transcription factor TFIIB","S300-II"],"length_aa":316,"mass_kda":34.8,"function":"General transcription factor that plays a role in transcription initiation by RNA polymerase II (Pol II). Involved in the pre-initiation complex (PIC) formation and Pol II recruitment at promoter DNA (PubMed:12931194, PubMed:1517211, PubMed:1876184, PubMed:1946368, PubMed:27193682, PubMed:3029109, PubMed:3818643, PubMed:7601352, PubMed:8413225, PubMed:8515820, PubMed:8516311, PubMed:8516312, PubMed:9420329). Together with the TATA box-bound TBP forms the core initiation complex and provides a bridge between TBP and the Pol II-TFIIF complex (PubMed:8413225, PubMed:8504927, PubMed:8515820, PubMed:8516311, PubMed:8516312). Released from the PIC early following the onset of transcription during the initiation and elongation transition and reassociates with TBP during the next transcription cycle (PubMed:7601352). Associates with chromatin to core promoter-specific regions (PubMed:12931194, PubMed:24441171). Binds to two distinct DNA core promoter consensus sequence elements in a TBP-independent manner; these IIB-recognition elements (BREs) are localized immediately upstream (BREu), 5'-[GC][GC][GA]CGCC-3', and downstream (BREd), 5'-[GA]T[TGA][TG][GT][TG][TG]-3', of the TATA box element (PubMed:10619841, PubMed:16230532, PubMed:7675079, PubMed:9420329). Modulates transcription start site selection (PubMed:10318856). Also exhibits autoacetyltransferase activity that contributes to the activated transcription (PubMed:12931194)","subcellular_location":"Nucleus; Chromosome","url":"https://www.uniprot.org/uniprotkb/Q00403/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/GTF2B","classification":"Common Essential","n_dependent_lines":1207,"n_total_lines":1208,"dependency_fraction":0.9991721854304636},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"POLR2A","stoichiometry":10.0},{"gene":"POLR2B","stoichiometry":10.0},{"gene":"POLR2C","stoichiometry":10.0},{"gene":"POLR2F","stoichiometry":10.0},{"gene":"POLR2G","stoichiometry":10.0},{"gene":"POLR2E","stoichiometry":4.0},{"gene":"POLR2H","stoichiometry":4.0},{"gene":"POLR2I","stoichiometry":4.0},{"gene":"POLR2K","stoichiometry":4.0},{"gene":"MED11","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/GTF2B","total_profiled":1310},"omim":[{"mim_id":"617680","title":"SSU72 HOMOLOG, RNA POLYMERASE II CTD PHOSPHATASE; SSU72","url":"https://www.omim.org/entry/617680"},{"mim_id":"610252","title":"MICRO RNA 1-2; MIR1-2","url":"https://www.omim.org/entry/610252"},{"mim_id":"609326","title":"MICRO RNA 1-1; MIR1-1","url":"https://www.omim.org/entry/609326"},{"mim_id":"608899","title":"GTF2I REPEAT DOMAIN-CONTAINING PROTEIN 2, ALPHA","url":"https://www.omim.org/entry/608899"},{"mim_id":"608431","title":"G3BP STRESS GRANULE ASSEMBLY FACTOR 1; G3BP1","url":"https://www.omim.org/entry/608431"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Nuclear bodies","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/GTF2B"},"hgnc":{"alias_symbol":["TFIIB"],"prev_symbol":[]},"alphafold":{"accession":"Q00403","domains":[{"cath_id":"1.10.472.10","chopping":"109-201","consensus_level":"high","plddt":93.8103,"start":109,"end":201},{"cath_id":"1.10.472.10","chopping":"210-311","consensus_level":"high","plddt":94.3433,"start":210,"end":311}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q00403","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q00403-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q00403-F1-predicted_aligned_error_v6.png","plddt_mean":87.25},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GTF2B","jax_strain_url":"https://www.jax.org/strain/search?query=GTF2B"},"sequence":{"accession":"Q00403","fasta_url":"https://rest.uniprot.org/uniprotkb/Q00403.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q00403/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q00403"}},"corpus_meta":[{"pmid":"7675079","id":"PMC_7675079","title":"Crystal 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\"confidence_rationale\": \"Tier 1-2 — recombinant protein binding assay demonstrating direct interaction, replicated across multiple labs\",\n      \"pmids\": [\"1922364\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"TFIIB contains a region with amino acid sequence similarity to bacterial sigma factors, consistent with an analogous role in promoter recognition; it also contains a large imperfect repeat and clusters of basic residues, suggesting it serves as a bridge between TFIID and RNA polymerase II during preinitiation complex assembly.\",\n      \"method\": \"cDNA cloning, sequencing, sequence homology analysis, purification to homogeneity\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — original cloning and purification paper with functional characterization, widely cited foundational work\",\n      \"pmids\": [\"1946368\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"S300-II (TFIIB) directly interacts with members of the steroid hormone receptor superfamily (COUP-TF, estrogen receptor, progesterone receptor) via protein-protein interactions, independent of adaptor proteins, identifying TFIIB as a direct target of nuclear receptor transactivators.\",\n      \"method\": \"Recombinant protein-protein interaction assays with purified proteins\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct binding with recombinant proteins, replicated with multiple receptor family members\",\n      \"pmids\": [\"1517211\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"The yeast SUA7 gene encodes a TFIIB homolog that is required for normal transcription start site selection in vivo; sua7 mutations cause downstream shifts in transcription initiation at multiple loci (cyc1, ADH1), establishing TFIIB's role in start site selection.\",\n      \"method\": \"Genetic suppressor screen, molecular cloning, primer extension analysis of transcripts\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic and molecular analysis in yeast model organism, replicated at multiple loci\",\n      \"pmids\": [\"1547497\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"TFIIB consists of two separable functional domains: the C-terminal core domain (TFIIBc) interacts with TBP-DNA complex, while the N-terminal domain is required for recruitment of RNA polymerase II-TFIIF into the initiation complex. Mutagenesis of cysteine residues in the N-terminal zinc finger blocks Pol II-TFIIF recruitment without impairing TBP binding.\",\n      \"method\": \"Limited proteolysis domain mapping; mutagenesis of cysteine codons; gel mobility-shift assays; in vitro transcription assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal methods (proteolysis, mutagenesis, in vitro transcription), replicated across labs\",\n      \"pmids\": [\"8516312\", \"8515820\", \"8516311\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Drosophila TAFII40 directly binds both the VP16 activation domain and TFIIB, suggesting a ternary interaction among activator, coactivator, and TFIIB. Antibodies against dTAFII40 inhibit GAL4-VP16 activation without affecting basal transcription.\",\n      \"method\": \"In vitro protein-protein interaction assays; affinity chromatography; antibody inhibition\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct binding assays with multiple orthogonal methods, functional antibody inhibition\",\n      \"pmids\": [\"8221891\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"HSV ICP4 forms a tripartite complex with TFIIB and TBP/TFIID on promoter DNA containing TATA box and ICP4-binding site; protein-protein interactions among all three proteins increase the affinity of ICP4 and TBP for their respective binding sites.\",\n      \"method\": \"Gel retardation assays, DNase I footprinting, use of mutant ICP4 derivatives\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple biochemical methods with mutant analysis\",\n      \"pmids\": [\"8392607\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"TFIIB core (C-terminal domain) forms a compact, protease-resistant structure that retains TBP binding but cannot support transcription. The N-terminal region mediates direct interaction with RNA Pol II (in association with TFIIF), and RNA Pol II may induce a conformational change in TFIIB leading to cryptic DNA-binding activity.\",\n      \"method\": \"Limited proteolysis, in vitro transcription, gel mobility-shift, DNase I footprinting\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple biochemical methods, conformational model validated by protease sensitivity\",\n      \"pmids\": [\"8413225\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Specific TFIIB mutations (sua7-1: E62K; sua7-2: E62K; sua7-3: R78C) define conserved residues adjacent to the zinc finger of TFIIB as critical determinants of transcription start site selection. Double-mutant analysis suggests an E62-R78 salt bridge as an important structural element in this domain.\",\n      \"method\": \"Site-directed mutagenesis, reciprocal charge-swap double mutants, in vivo suppressor analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — comprehensive mutagenesis with reciprocal charge swaps and in vivo phenotype validation\",\n      \"pmids\": [\"7982976\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"SUA8 mutations in the largest subunit of RNA polymerase II (RPB1) cause downstream shifts in transcription start site selection similar to sua7 (TFIIB) mutations; sua7 sua8 double mutants show synthetic lethality and non-allelic non-complementation, establishing a functional interaction between TFIIB and RPB1 in start site selection.\",\n      \"method\": \"Genetic suppressor screen, molecular cloning, synthetic lethality analysis, transcript mapping\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with multiple alleles and synthetic lethality\",\n      \"pmids\": [\"8264591\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"The proline-rich activation domain of CTF1 selectively interacts with TFIIB (but not TBP) and facilitates TFIIB recruitment to TBP-DNA complexes, demonstrating that different activator types can target TFIIB for preinitiation complex assembly.\",\n      \"method\": \"In vitro protein-protein interaction; gel retardation assays monitoring TFIIB recruitment\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct binding plus functional recruitment assay in both human and yeast systems\",\n      \"pmids\": [\"8183887\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Crystal structure of the TFIIB/TBP/TATA-element ternary complex at 2.7 Å reveals that core TFIIB resembles cyclin A and recognizes the preformed TBP-DNA complex through protein-protein and protein-DNA interactions; the N-terminal domain of core TFIIB forms the downstream surface of the ternary complex, potentially fixing the transcription start site.\",\n      \"method\": \"X-ray crystallography at 2.7 Å resolution\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure of the ternary complex, foundational structural paper\",\n      \"pmids\": [\"7675079\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"NMR structure of human TFIIB core domain (TFIIBc) reveals two direct repeats with similar alpha-helical folds (resembling cyclin A) conferring pseudo-twofold symmetry; an extensive central basic surface including an amphipathic alpha helix is critical for TFIIB function as a bridge between TBP-promoter complex and RNA Pol II.\",\n      \"method\": \"Multidimensional heteronuclear NMR spectroscopy\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR structure with functional validation of identified surface residues\",\n      \"pmids\": [\"7671313\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Monomeric Drosophila Krüppel (Kr) activates transcription through interaction with TFIIB when acting near the basal promoter, whereas Kr dimers repress transcription through interaction with TFIIE beta.\",\n      \"method\": \"In vitro protein-protein interaction assays, in vitro transcription with purified factors\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct protein interaction assays with functional transcription readout distinguishing activator vs. repressor modes\",\n      \"pmids\": [\"7753175\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"VDR (vitamin D receptor) directly binds TFIIB via select protein domains; co-transfection of VDR and TFIIB cooperatively activates a 1,25(OH)2D3-responsive reporter in a ligand-dependent manner in P19 cells, demonstrating functional interaction between TFIIB and a nuclear hormone receptor in vivo.\",\n      \"method\": \"GST fusion protein-protein binding assays; cotransfection reporter assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct binding assay plus in vivo functional confirmation by cotransfection\",\n      \"pmids\": [\"7878015\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Hydroxyl-radical footprinting and gel mobility-shift assays reveal that TFIIB binds beneath the concave surface of TBP, contacting DNA both upstream and downstream of the TATA box; TFIIB requires at least 7 bp of DNA on either side of the TATA box to form a stable TFIIB-TBP-DNA complex.\",\n      \"method\": \"Gel mobility-shift assays, hydroxyl-radical footprinting mapped onto TBP-DNA crystal structure\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — orthogonal biochemical methods with structural interpretation\",\n      \"pmids\": [\"7637813\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"High-resolution protein-DNA photocrosslinking reveals TFIIA and TFIIB make more extensive interactions with promoter DNA than previously anticipated; TBP, TFIIA, and TFIIB together surround promoter DNA for two turns of the helix, forming a 'cylindrical clamp' effectively topologically linked to promoter DNA.\",\n      \"method\": \"Site-specific protein-DNA photocrosslinking in binary, ternary, and quaternary complexes\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — novel photocrosslinking approach with systematic mapping\",\n      \"pmids\": [\"8855228\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"The N-terminal A/B domain (amino acids 21-30, containing a basic amino acid cluster) of thyroid hormone receptor alpha (T3Rα) is essential for transcriptional activation and directly interacts with TFIIB (residues 178-201); this interaction is required for T3Rα-mediated transcriptional activation.\",\n      \"method\": \"In vitro binding studies with recombinant proteins; deletion and mutagenesis analysis; transient transfection\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — domain mapping by mutagenesis with direct binding assays and in vivo functional validation\",\n      \"pmids\": [\"7623841\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Protease footprinting reveals two regions of TFIIB protected by the VP16 activation domain and one region protected by TAFII40 (overlapping with the VP16 site), defining a regulatory surface on TFIIB that serves as an interface for both activators and coactivators.\",\n      \"method\": \"Protease footprinting with broad-specificity proteases on 32P-labeled TFIIB\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — novel methodology directly visualizing binding surfaces on TFIIB\",\n      \"pmids\": [\"7597078\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Diverse activators (acidic, proline-rich, glutamine-rich) fail to recruit mutant forms of TFIIB that cannot respond to activators, demonstrating that activator-mediated TFIIB recruitment is a central and universal step in transcriptional activation; TFIIB dissociates after each round of transcription, requiring reassembly for each reinitiation.\",\n      \"method\": \"In vitro transcription with TFIIB mutants; gel retardation assays for TFIIB recruitment\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple activator classes tested, reinitiation mechanism demonstrated biochemically\",\n      \"pmids\": [\"7583100\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"RAP74 (large subunit of TFIIF) directly binds TFIIB through its C-terminal region, while RAP30 binds TFIIB at an overlapping region; RAP74 blocks TFIIB-RAP30 binding by simultaneously binding TFIIB and RAP30, indicating that when TFIIF is intact, TFIIB-TFIIF contact is maintained through RAP74.\",\n      \"method\": \"Deletion mutagenesis, in vitro binding assays, in vitro transcription\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — domain mapping with direct binding assays and functional transcription data\",\n      \"pmids\": [\"8662660\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"IRF-1 and IRF-2 bind to TFIIB; IRF-1 and TFIIB cooperatively enhance ISRE promoter activity both in vitro and in vivo; this cooperation is independent of the TATA sequence but dependent on the initiator sequence (Inr) and is cell-type specific.\",\n      \"method\": \"In vitro protein binding assays; in vitro transcription; cotransfection reporter assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct binding plus orthogonal in vitro and in vivo functional data\",\n      \"pmids\": [\"8887661\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"The yeast SUB1 protein (homolog of human co-activator PC4) binds TFIIB in vitro and specifically inhibits TBP-TFIIB-promoter complex formation; overexpression of SUB1 suppresses TFIIB alleles E62G and R78H, suggesting SUB1 facilitates TFIIB release during transcription initiation.\",\n      \"method\": \"Genetic suppressor screen; in vitro binding assays; gel retardation for complex formation\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis combined with direct biochemical binding and complex formation assays\",\n      \"pmids\": [\"8617240\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"TFIIB directly interacts with HBV pX protein in vivo (co-immunoprecipitation from nuclear extracts); pX bridges an otherwise inefficient TFIIB-POLII interaction, using TFIIB as a molecular scaffold for transcriptional coactivation.\",\n      \"method\": \"Co-immunoprecipitation from nuclear extracts; TFIIB mutant analysis; in vitro and in vivo transcription assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — co-IP from nuclear extracts combined with mutant TFIIB functional dissection in vivo and in vitro\",\n      \"pmids\": [\"9488473\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"TFIIB mediates sequence-specific DNA binding by recognizing a defined element upstream of the TATA box (BRE), and this recognition cooperates with TBP-TATA binding as a codeterminant of promoter strength.\",\n      \"method\": \"Mutagenesis, in vitro binding assays, in vitro transcription\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct demonstration of sequence-specific DNA binding by TFIIB with functional consequences\",\n      \"pmids\": [\"9660923\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"The N-terminal region of yeast TFIIB contains two separable adjacent functional domains: the zinc ribbon fold mediates stable RNA Pol II binding, while a highly conserved homology block C-terminal to the zinc ribbon controls transcription start site selection.\",\n      \"method\": \"Site-directed mutagenesis; in vitro transcription; start site selection assays in vitro and in vivo; pulldown assays with purified Pol II\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic mutagenesis with multiple orthogonal functional assays\",\n      \"pmids\": [\"9651390\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"NMR analysis shows TFIIB core domain is conformationally flexible in solution; binding of the VP16 activation domain or the N-terminal zinc domain induces chemical shift changes in the first repeat and interrepeat linker of TFIIBc, suggesting TFIIB is pliable and can be modulated by activator interactions to prime binding to TBP-DNA complexes.\",\n      \"method\": \"1H-15N NMR, backbone 15N relaxation measurements, comparison with crystal structure\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR solution structure with dynamics analysis and direct activator interaction mapping\",\n      \"pmids\": [\"9609687\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Genetic epistasis in yeast establishes functional interactions among TFIIB, Ssu72, and Sub1 that are allele-specific and linked specifically to TFIIB alleles affecting transcription start site selection, placing Ssu72 and Sub1 in the same functional pathway as TFIIB for start site selection.\",\n      \"method\": \"Error-prone PCR mutagenesis library, genetic suppressor/enhancer analysis, allele-specificity testing\",\n      \"journal\": \"Genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — comprehensive allele-specific epistasis analysis\",\n      \"pmids\": [\"10511545\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The TFIIB S53P mutation specifically impairs activation of PHO5 and ADH2 without affecting basal transcription; Pho4 directly interacts with TFIIB in vitro and induces a conformational change in TFIIB (detected by enhanced V8 protease sensitivity), suggesting certain activators function by inducing conformational changes in TFIIB.\",\n      \"method\": \"Yeast mutagenesis screen; in vitro binding assay; protease sensitivity assay; reporter gene analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — combined genetic and biochemical approaches demonstrating conformational change\",\n      \"pmids\": [\"10077585\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Fcp1p (CTD phosphatase) directly binds the first cyclin-like repeat in the TFIIB core domain via a KEFGK motif shared by TFIIB and the RAP74 subunit of TFIIF; this interaction is functionally significant for transcriptional activation.\",\n      \"method\": \"Deletion/point mutagenesis of Fcp1p; direct binding assays; genetic synthetic phenotype analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — domain mapping by mutagenesis combined with direct binding and genetic interaction data\",\n      \"pmids\": [\"11003641\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The BRE (TFIIB recognition element) upstream of the TATA box suppresses basal transcription, and activator proteins can disrupt the TFIIB-BRE interaction within promoter-bound complexes, revealing a novel activator function in modulating core promoter recognition by TFIIB.\",\n      \"method\": \"In vitro transcription assays; protein-DNA interaction assays\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional dissection with clear mechanistic interpretation\",\n      \"pmids\": [\"11711430\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Crystal structure of RNA Pol II-TFIIB cocrystal at 4.5 Å reveals three functional features: the TFIIB zinc ribbon domain contacts the Pol II dock domain near the RNA exit path; the B-finger domain inserts into the Pol II active center; and the C-terminal domain orients promoter DNA for unwinding and transcription initiation.\",\n      \"method\": \"X-ray crystallography at 4.5 Å\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution cocrystal structure revealing direct mechanism of Pol II-TFIIB interaction\",\n      \"pmids\": [\"14963322\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Site-specific photocrosslinking and directed hydroxyl radical probing map the TFIIB zinc ribbon domain to the Pol II Dock domain surface overlapping the RNA exit point within the preinitiation complex, defining a general mechanism for TFIIB-like factor interaction with RNA polymerases.\",\n      \"method\": \"Site-specific photocrosslinking, directed hydroxyl radical probing, mutational analysis\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple direct mapping approaches with mutagenesis validation\",\n      \"pmids\": [\"14536083\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Biochemical probes on TFIIB reveal that in full PICs (not in the smaller Pol II-TFIIB complex), TFIIB linker and core domains are positioned over the central cleft and wall of Pol II; TFIIF subunit Tfg1 is in close proximity to TFIIB B-finger, linker, and core domains, suggesting close cooperation between TFIIB and TFIIF during initiation.\",\n      \"method\": \"Site-specific chemical probing of TFIIB within the PIC\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic biochemical mapping across the full PIC\",\n      \"pmids\": [\"15479635\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Functional interaction between TFIIB and the Rpb2 subunit of RNA Pol II is established by suppressor genetics; the B-finger domain (R78C) of TFIIB functionally interacts with the lobe domain (G369S) of Rpb2 in start site selection; TFIIB R78C alters abortive initiation patterns without precluding initiation.\",\n      \"method\": \"Genetic suppressor screen; in vitro transcription; run-on transcription; abortive initiation assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis combined with multiple biochemical transcription assays\",\n      \"pmids\": [\"15082791\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"TFIIB defines a downstream core promoter element (BREd, distinct from the upstream BRE); two independent DNA-binding motifs in TFIIB recognize elements flanking the TATA box and cooperate in transcription regulation in a promoter context-dependent manner.\",\n      \"method\": \"In vitro transcription assays; protein-DNA binding assays; mutagenesis\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional dissection with clear definition of two independent DNA-binding domains\",\n      \"pmids\": [\"16230532\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Regardless of TATA-to-start-site spacing, the upstream transcription bubble edge forms 20 bp from TATA; the B-finger of TFIIB causes pausing at +7 to +9 within the complex, and bubble collapse (reannealing of upstream ~8 bases when bubble reaches 18 bp and RNA is ≥7 nt) suppresses this pausing and marks the promoter clearance transition.\",\n      \"method\": \"In vitro transcription with systematically varied promoter spacing; bubble mapping; nucleotide depletion\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — systematic in vitro dissection of bubble dynamics and TFIIB B-finger role in clearance\",\n      \"pmids\": [\"15989968\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"TFIIB has a transcription-independent role in gene looping in yeast: TFIIB crosslinks to both promoter and terminator regions of genes; the E62K TFIIB mutation adversely affects looping at multiple genes; TFIIB association with the terminator is dependent on the Ssu72 component of the CPF 3' end processing complex and is independent of TBP.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP); chromosome conformation capture (3C); genetic analysis with TFIIB and Ssu72 mutants\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (ChIP, 3C) with genetic validation\",\n      \"pmids\": [\"17803944\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Expansion of the polyglutamine tract in TBP (SCA17) enhances the TBP-TFIIB interaction while reducing TBP dimerization; this leads to decreased TFIIB occupancy of the Hspb1 promoter and downregulation of HSPB1 in SCA17 transgenic mice; overexpression of TFIIB alleviates mutant TBP-induced neuritic defects.\",\n      \"method\": \"Transgenic mouse model; co-immunoprecipitation; ChIP; neuritic defect rescue\",\n      \"journal\": \"Nature neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo mouse model with multiple biochemical methods and functional rescue\",\n      \"pmids\": [\"17994014\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Crystal structure of the complete Pol II-TFIIB complex at 4.3 Å reveals initiation mechanism: B-core domain binds Pol II wall to position promoter DNA over the active centre cleft; B-linker binds the Pol II rudder and clamp coiled-coil to assist DNA opening; B-reader approaches the active site to assist template strand scanning and TSS recognition; RNA synthesis and DNA rewinding displace B-reader and B-linker to trigger TFIIB release and elongation.\",\n      \"method\": \"X-ray crystallography at 4.3 Å; complementary functional mutagenesis data\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure with complementary functional validation\",\n      \"pmids\": [\"19820686\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"A 3.8 Å crystal structure of the Pol II-TFIIB complex reveals the C-terminal region of TFIIB positioned above the polymerase active center cleft, and the linker between N- and C-terminal regions snaking down toward the active center; together with the prior 4.5 Å structure, these define two distinct conformational states of TFIIB in the complex.\",\n      \"method\": \"X-ray crystallography at 3.8 Å\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — complementary crystal structure clarifying TFIIB domain positioning\",\n      \"pmids\": [\"19965383\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"TFIIB is phosphorylated at serine 65 in vivo within preinitiation complexes; this phosphorylation occurs after RNA Pol II CTD serine 5 phosphorylation but before productive initiation; phospho-S65 TFIIB regulates interaction with CstF-64 (component of the CstF cleavage/polyadenylation complex), directing CstF recruitment to the terminator and linking promoter to terminator function.\",\n      \"method\": \"In vivo phosphorylation mapping; PIC assembly analysis; ChIP; co-immunoprecipitation with CstF-64\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods identifying the modification, its writer order, and functional consequence\",\n      \"pmids\": [\"20226668\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"TFIIF is not required for RNA Pol II initiation or promoter clearance per se, but is essential for stabilizing TFIIB in early elongation complexes; without TFIIF, TFIIB can be lost immediately after initiation rather than at the normal +12 to +13 displacement point.\",\n      \"method\": \"Casein kinase 2 phosphorylation of TFIIF to generate TFIIF-depleted PICs; in vitro transcription; factor retention analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic dissection of factor requirements with controlled biochemical system\",\n      \"pmids\": [\"21896726\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Crystal structures of the Pol II-TFIIB complex at 3.4 Å and of an initially transcribing complex (with DNA template and 6-nt RNA) reveal: the complete B-reader does not reach the active site but binds DNA template strand upstream to assist initiator recognition and TSS positioning; TFIIB rearranges active-site residues and induces metal B binding; TFIIB prevents tilting of the DNA-RNA hybrid; when RNA grows beyond 6 nt, the B-reader loop directs RNA to its exit tunnel; when RNA reaches 12-13 nt, it clashes with TFIIB, triggering TFIIB displacement and elongation complex formation.\",\n      \"method\": \"X-ray crystallography at 3.4 Å; initially transcribing complex structure; functional mutagenesis\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structures of multiple complexes with functional validation\",\n      \"pmids\": [\"23151482\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Single-molecule analysis reveals TFIIB binding to the promoter is highly transient (average residence time ~1.5 sec) when TFIID and TFIIA are present, but undergoes a transient-to-stable transition only in the presence of Pol II-TFIIF, establishing Pol II-TFIIF recruitment as a checkpoint for TFIIB stabilization in PIC assembly.\",\n      \"method\": \"Single-molecule fluorescence microscopy; live-cell imaging; in vitro reconstituted transcription system\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — novel single-molecule approach revealing dynamics invisible to ensemble methods, validated by live-cell imaging\",\n      \"pmids\": [\"27798851\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Mediator interacts with TFIIB through its middle module subunit Med10; this Mediator-TFIIB interaction has a global role in PIC assembly genome-wide, and the amplitude of Mediator's effect on PIC formation is dependent on promoter architecture (TATA elements, nucleosome occupancy).\",\n      \"method\": \"In vivo ChIP, in vitro PIC assembly assays, genome-wide analysis, Med10 mutant analysis\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal approaches (in vivo, in vitro, genome-wide) identifying specific interaction domain\",\n      \"pmids\": [\"27688401\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Rapid acute depletion of TFIIB in HAP1 cells shows the largest general effect on RNA Pol II promoter activity among GTFs tested; TFIIB depletion also correlates with apparent transcription termination defects downstream of genes, consistent with its role in linking initiation and termination.\",\n      \"method\": \"Rapid auxin-induced depletion; precision nuclear run-on sequencing (PRO-Seq) genome-wide\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genome-wide functional measurement with acute depletion across >70,000 promoters\",\n      \"pmids\": [\"35947745\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TFIIB (GTF2B) is a general transcription factor that bridges promoter-bound TFIID/TBP and RNA Polymerase II during preinitiation complex (PIC) assembly: its C-terminal cyclin-fold core domain recognizes TBP and flanking promoter DNA elements (BREu upstream and BREd downstream of the TATA box), while its N-terminal zinc ribbon domain contacts the Pol II dock domain to recruit Pol II; upon PIC formation, the B-linker assists DNA opening and the B-reader positions the template strand for transcription start site selection; after synthesis of ~12-13 nt RNA, the growing transcript clashes with TFIIB, triggering its displacement to allow elongation complex formation; TFIIB is also phosphorylated at Ser65 within the PIC, linking initiation to 3' end processing/termination machinery (CstF), and has a transcription-independent role in gene loop formation between promoters and terminators.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"GTF2B (TFIIB) is a general transcription factor essential for RNA polymerase II preinitiation complex (PIC) assembly, transcription start site selection, promoter clearance, and coupling of initiation to termination. Its C-terminal cyclin-fold core domain recognizes TBP on promoter DNA and contacts flanking BRE elements upstream and downstream of the TATA box, while its N-terminal zinc ribbon domain binds the Pol II dock domain to recruit Pol II–TFIIF; within the PIC, the B-linker assists DNA strand opening and the B-reader positions the template strand for start site selection, with TFIIB displacement triggered by clash with the growing RNA transcript at 12–13 nucleotides to permit elongation [PMID:19820686, PMID:23151482, PMID:9660923, PMID:16230532]. TFIIB is a direct target of diverse transcriptional activators—including acidic (VP16), proline-rich (CTF1), and nuclear receptor classes—whose binding induces conformational changes that modulate TFIIB recruitment and PIC formation [PMID:1922364, PMID:1517211, PMID:10077585, PMID:7583100]. Beyond initiation, TFIIB is phosphorylated at Ser65 within the PIC, linking it to CstF-mediated 3′-end processing, and participates in gene loop formation between promoters and terminators via interaction with the Ssu72 phosphatase, establishing TFIIB as a physical and functional bridge coupling transcription initiation to termination [PMID:20226668, PMID:17803944, PMID:35947745].\",\n  \"teleology\": [\n    {\n      \"year\": 1991,\n      \"claim\": \"Cloning and purification of TFIIB revealed it as a single-polypeptide general transcription factor with structural homology to bacterial sigma factors and direct repeat architecture, establishing it as a bridge between TFIID and RNA Pol II, and identifying it as a direct target of acidic activators like VP16.\",\n      \"evidence\": \"cDNA cloning, sequence analysis, recombinant protein affinity chromatography with VP16\",\n      \"pmids\": [\"1946368\", \"1922364\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural model of TFIIB at this stage\", \"Mechanism of how activator binding stimulates PIC assembly unknown\"]\n    },\n    {\n      \"year\": 1992,\n      \"claim\": \"Yeast genetics showed that TFIIB (SUA7) is a determinant of transcription start site selection in vivo, shifting the understanding of TFIIB from a passive scaffold to an active participant in positioning the initiation site.\",\n      \"evidence\": \"Genetic suppressor screen at cyc1 and ADH1 loci; primer extension mapping of start sites in sua7 mutants\",\n      \"pmids\": [\"1547497\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of start site selection unknown\", \"Whether mammalian TFIIB performs the same function unclear\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Domain dissection established that TFIIB has a bipartite architecture: the C-terminal core binds TBP–DNA while the N-terminal zinc-finger region recruits RNA Pol II–TFIIF, resolving how one factor bridges promoter recognition and polymerase recruitment.\",\n      \"evidence\": \"Limited proteolysis, cysteine mutagenesis, gel-shift and in vitro transcription assays\",\n      \"pmids\": [\"8516312\", \"8515820\", \"8413225\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic resolution structure lacking\", \"Role of the linker between domains unknown\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Crystal and NMR structures of the TFIIB core domain and the TFIIB–TBP–TATA ternary complex revealed the cyclin-fold architecture and how TFIIB contacts DNA both upstream and downstream of the TATA box, providing the first atomic framework for understanding promoter recognition and start site positioning.\",\n      \"evidence\": \"X-ray crystallography at 2.7 Å; multidimensional NMR spectroscopy; hydroxyl-radical footprinting\",\n      \"pmids\": [\"7675079\", \"7671313\", \"7637813\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of TFIIB with Pol II not yet determined\", \"BRE sequence specificity not formally defined\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"TFIIB was shown to be a convergent target of diverse activator classes (acidic, proline-rich, glutamine-rich) and nuclear receptors, with activator binding inducing conformational changes on a defined regulatory surface, establishing TFIIB recruitment as a universal rate-limiting step in transcriptional activation.\",\n      \"evidence\": \"In vitro transcription with TFIIB mutants; protease footprinting; protein-protein binding with VDR, T3Rα, CTF1, VP16\",\n      \"pmids\": [\"7583100\", \"7597078\", \"7878015\", \"8183887\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of activator-induced conformational change unresolved\", \"Whether all promoters depend equally on TFIIB recruitment unknown\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"TFIIB was found to recognize a specific upstream DNA element (BRE) as a codeterminant of promoter strength, and the N-terminal zinc ribbon and adjacent B-finger were shown to have separable functions in Pol II binding versus start site selection, refining the functional map of TFIIB's N-terminal region.\",\n      \"evidence\": \"In vitro binding and transcription with promoter and TFIIB mutants; yeast mutagenesis\",\n      \"pmids\": [\"9660923\", \"9651390\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream BRE not yet identified\", \"Mechanism of B-finger action in start site selection unknown at atomic level\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"The first crystal structure of the Pol II–TFIIB complex revealed three key contacts: the zinc ribbon at the Pol II dock domain, the B-finger inserted into the active center, and the C-terminal domain orienting promoter DNA, providing a structural explanation for TFIIB's multifunctional role in initiation.\",\n      \"evidence\": \"X-ray crystallography at 4.5 Å; site-specific photocrosslinking; directed hydroxyl radical probing\",\n      \"pmids\": [\"14963322\", \"14536083\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Resolution insufficient to define B-reader contacts with template strand\", \"Initially transcribing complex structure lacking\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"A downstream BRE (BREd) was identified, showing TFIIB recognizes elements flanking both sides of the TATA box through two independent DNA-binding motifs, and the B-finger was shown to cause pausing at +7–9, with bubble collapse marking the promoter clearance transition.\",\n      \"evidence\": \"In vitro transcription with varied promoter spacing; bubble mapping; BREd mutagenesis\",\n      \"pmids\": [\"16230532\", \"15989968\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How BREu and BREd cooperate structurally in the full PIC unclear\", \"Whether bubble collapse is the sole trigger for TFIIB release unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"TFIIB was found to occupy both promoter and terminator regions of genes and to be required for gene loop formation in an Ssu72-dependent manner, revealing a transcription-independent structural role that physically links initiation and termination.\",\n      \"evidence\": \"ChIP and chromosome conformation capture (3C) in yeast with TFIIB and Ssu72 mutants\",\n      \"pmids\": [\"17803944\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether gene looping occurs in mammalian cells via TFIIB unknown\", \"Molecular contacts at the terminator not defined\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Higher-resolution Pol II–TFIIB crystal structures resolved the complete mechanism: B-linker assists DNA opening by binding the Pol II rudder, B-reader assists template scanning and TSS recognition, and RNA synthesis plus DNA rewinding displace B-reader/B-linker to trigger TFIIB release.\",\n      \"evidence\": \"X-ray crystallography at 4.3 Å and 3.8 Å with functional mutagenesis\",\n      \"pmids\": [\"19820686\", \"19965383\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of an actively transcribing complex with nascent RNA still needed\", \"Role of TFIIF in stabilizing TFIIB during this process not structurally resolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Phosphorylation of TFIIB at Ser65 within the PIC was shown to regulate interaction with CstF-64, directing 3′-end processing machinery recruitment and providing a molecular mechanism linking promoter-bound TFIIB to termination.\",\n      \"evidence\": \"In vivo phosphorylation mapping; ChIP; co-immunoprecipitation with CstF-64\",\n      \"pmids\": [\"20226668\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinase responsible for Ser65 phosphorylation not identified\", \"Whether this modification is universal across all Pol II genes unknown\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Crystal structures of the initially transcribing complex revealed that the B-reader binds template strand upstream of the active site for TSS positioning, directs RNA to the exit tunnel after 6 nt, and is displaced by clash with the growing RNA at 12–13 nt, completing the structural narrative of TFIIB function from initiation through clearance.\",\n      \"evidence\": \"X-ray crystallography at 3.4 Å of Pol II–TFIIB with DNA template and 6-nt RNA; mutagenesis\",\n      \"pmids\": [\"23151482\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full PIC structure with all GTFs not yet available at this resolution\", \"Dynamics of TFIIB displacement in vivo not directly measured\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Single-molecule and genome-wide studies showed that TFIIB promoter binding is highly transient (~1.5 s) until stabilized by Pol II–TFIIF arrival, and that Mediator contacts TFIIB through Med10 to facilitate PIC assembly genome-wide in a promoter architecture-dependent manner.\",\n      \"evidence\": \"Single-molecule fluorescence microscopy; ChIP genome-wide; Med10 mutant analysis in vitro and in vivo\",\n      \"pmids\": [\"27798851\", \"27688401\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How Mediator–TFIIB interaction is regulated at individual promoters unclear\", \"Structural basis of Med10–TFIIB contact unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Acute TFIIB depletion showed it has the largest effect on Pol II promoter activity among general transcription factors and confirmed termination defects downstream of genes, validating TFIIB's dual role in initiation and termination genome-wide in human cells.\",\n      \"evidence\": \"Auxin-induced degradation in HAP1 cells; PRO-seq genome-wide\",\n      \"pmids\": [\"35947745\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether termination defects are direct consequences of lost gene looping or lost CstF recruitment not resolved\", \"Promoter-specific dependencies on TFIIB not fully characterized\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the identity of the Ser65 kinase, the structural basis of gene loop formation at terminators, whether TFIIB displacement dynamics differ across promoter classes in vivo, and how Mediator–TFIIB and activator–TFIIB interactions are coordinated within the complete PIC.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Ser65 kinase identity unknown\", \"Structural basis of TFIIB at terminators not determined\", \"Complete human PIC structure with TFIIB at atomic resolution not available\", \"In vivo single-molecule dynamics of TFIIB displacement during elongation transition not measured\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [11, 15, 24, 35]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [1, 3, 4, 11, 39, 46]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [4, 7, 31, 39]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [37, 41, 46]},\n      {\"term_id\": \"GO:0005654\", \"supporting_discovery_ids\": [33, 41, 44]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [1, 3, 4, 11, 31, 39, 43, 46]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [41, 37, 46]}\n    ],\n    \"complexes\": [\n      \"RNA Polymerase II preinitiation complex (PIC)\"\n    ],\n    \"partners\": [\n      \"TBP\",\n      \"RPB1\",\n      \"RPB2\",\n      \"RAP74\",\n      \"RAP30\",\n      \"CSTF2\",\n      \"SSU72\",\n      \"MED10\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}