{"gene":"TAF1C","run_date":"2026-04-28T21:42:58","timeline":{"discoveries":[{"year":1992,"finding":"SL1 (selectivity factor 1) is a complex containing TBP (TATA-binding protein) and three distinct TBP-associated factors (TAFIs); purified TAFIs reconstituted with recombinant TBP complement SL1 activity, demonstrating that TBP plus novel associated factors are integral components of SL1 and are necessary for RNA polymerase I promoter selectivity.","method":"Column chromatography, glycerol gradient sedimentation, antibody depletion, reconstitution in vitro transcription","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 — reconstitution in vitro with purified components, replicated in multiple subsequent studies","pmids":["1547496"],"is_preprint":false},{"year":1988,"finding":"SL1 has no sequence-specific DNA binding activity on its own, but cooperates with UBF1 through direct protein-protein interactions to form a complex at UCE and core promoter elements, enabling RNA polymerase I transcriptional activation.","method":"DNase I footprinting, in vitro transcription reconstitution, purification","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — DNase I footprinting and in vitro transcription reconstitution, foundational paper replicated extensively","pmids":["3413483"],"is_preprint":false},{"year":1994,"finding":"The three TAFI subunits of SL1 (TAFI110, TAFI63, TAFI48) each bind individually and specifically to TBP; they also interact with each other to form a stable TBP-TAF complex. TBP binding by SL1 TAFIs is mutually exclusive with binding by TFIID subunits (TAFII250 and TAFII150), indicating that promoter- and RNA polymerase-selective TBP-TAF complexes are formed through mutually exclusive TBP binding.","method":"Subunit interaction assays, reconstitution, co-immunoprecipitation","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — reconstitution with recombinant subunits and binding specificity assays in a single rigorous study","pmids":["7801123"],"is_preprint":false},{"year":1994,"finding":"In vivo and in vitro assembly of functional SL1 complexes from recombinant TAFIs (110, 63, 48) and TBP reconstitutes transcriptionally active SL1 that supports transcription from the human rRNA gene promoter; partial complexes without TBP do not efficiently direct transcription, demonstrating that all four subunits are necessary and sufficient.","method":"Reconstitution in vitro transcription, recombinant protein assembly","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — complete reconstitution with defined recombinant subunits and functional transcription assay","pmids":["7801130"],"is_preprint":false},{"year":1994,"finding":"The conserved core domain of TBP alone (without the N-terminal domain) is sufficient to assemble functional SL1, and TBP directly interacts with the smallest SL1 subunit TAFI48, as shown by in vitro protein-protein interaction assay.","method":"Immunopurification of epitope-tagged TBP deletion mutants, in vitro protein-protein interaction assay, in vitro transcription","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — deletion mutagenesis with functional transcription readout and direct binding assay","pmids":["8058785"],"is_preprint":false},{"year":1997,"finding":"Mouse Pol I-specific TAFIs were cloned; human and mouse TAFI subunits can form stable chimeric complexes containing stoichiometric amounts of TBP and TAFIs, indicating conserved protein-protein contacts underlying SL1 assembly, while species-specific promoter selectivity results from cumulative subtle sequence differences among individual subunits.","method":"cDNA cloning, chimeric complex assembly, in vitro transcription","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — reconstitution of chimeric complexes with functional transcription assay","pmids":["9050847"],"is_preprint":false},{"year":1998,"finding":"SL1 is inactivated during mitosis by cdc2/cyclin B-directed phosphorylation of two subunits, TBP and hTAFI110 (TAF1C), and reactivated by dephosphorylation; mitotic phosphorylation impairs the interaction of SL1 with UBF, preventing pre-initiation complex formation and shutting down rDNA transcription at mitosis.","method":"Cell-free transcription reconstitution, phosphorylation assays, protein-protein interaction studies, mitotic HeLa cell extracts","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — reconstituted cell-free system with biochemical phosphorylation assays and multiple orthogonal approaches","pmids":["9857193"],"is_preprint":false},{"year":1998,"finding":"Phosphorylation by cdc2/cyclin B inactivates SL1 (the TBP-containing factor) and abrogates Pol I transcription during mitosis; this provides a common mechanism for mitotic silencing of all three nuclear RNA polymerases via reversible inactivation of their respective TBP-TAF complexes.","method":"In vitro transcription in asynchronous vs. mitotic HeLa cell extracts, phosphorylation assays","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 — multiple approaches confirming cdc2/cyclin B phosphorylation inactivates SL1 in vitro","pmids":["9811537"],"is_preprint":false},{"year":1996,"finding":"TBP/SL1 co-localizes with UBF and RNA polymerase I at sites of rRNA transcription in nucleoli of actively growing cells; during mitosis, TBP co-localizes with TAFIs (including TAF1C), UBF, and RNA polymerase I on chromosomal rRNA gene regions; anti-TBP antibodies co-immunoprecipitate TBP and TAFI63, confirming in vivo complex formation.","method":"Immunofluorescence microscopy, co-immunoprecipitation from cell extracts, actinomycin D treatment","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — direct localization by immunofluorescence combined with co-IP and functional perturbation","pmids":["8609157"],"is_preprint":false},{"year":1999,"finding":"The carboxy-terminal activation domain of UBF makes direct contact with the TBP-TAFI complex SL1; UBF phosphorylation at the C-terminus is required for SL1 interaction and recruitment to the rDNA promoter, as alkaline phosphatase treatment of UBF abolishes its ability to interact with SL1 and activate transcription.","method":"Protein-protein interaction assays with UBF deletion mutants, alkaline phosphatase treatment, DNase I footprinting, in vitro transcription","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 — multiple orthogonal biochemical assays with defined deletion mutants and phosphatase treatment","pmids":["10082553"],"is_preprint":false},{"year":2001,"finding":"PCAF acetylates TAF(I)68 (TAF1C), the second largest subunit of TIF-IB/SL1; acetylation by PCAF enhances binding of TAFI68 to the rDNA promoter and stimulates Pol I transcription; the NAD+-dependent deacetylase mSir2a deacetylates TAFI68 and represses Pol I transcription, demonstrating reversible acetylation as a regulatory mechanism.","method":"In vitro acetyltransferase assay, in vitro transcription reconstitution, promoter binding assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — in vitro acetylation assay with identified writer (PCAF) and eraser (mSir2a), functional transcription readout","pmids":["11250901"],"is_preprint":false},{"year":2001,"finding":"hRRN3 interacts directly with TAF(I)110 and TAF(I)63 subunits of SL1; this interaction defines a transcriptionally competent subpopulation of Pol I (I beta); blocking the hRRN3-SL1 connection prevents recruitment of Pol I to the rDNA promoter, establishing hRRN3 as the factor linking initiation-competent Pol I to SL1.","method":"Co-immunoprecipitation, in vitro interaction assays, Pol I transcription assays, siRNA depletion","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP and functional transcription assays establishing pathway position","pmids":["11250903"],"is_preprint":false},{"year":2000,"finding":"Rb interacts directly with UBF (requiring a functional A/B pocket) but does not inhibit UBF binding to DNA; instead, the UBF-Rb complex blocks the interaction of UBF with SL1 (using the 48 kDa subunit as SL1 marker), thereby repressing RNA Pol I transcription; p130 but not p107 similarly associates with UBF and represses rDNA transcription.","method":"Direct protein interaction assays, DNase footprinting, band-shift assays, immunoprecipitation","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 1–2 — multiple direct binding assays, DNase footprinting, and functional transcription measurements","pmids":["11042686"],"is_preprint":false},{"year":1997,"finding":"SV40 large T antigen directly binds SL1 in vitro and in SV40-infected cells; the interaction occurs with three SL1 subunits: TBP, TAFI48, and TAFI110; large T antigen mutants that cannot bind SL1 are unable to stimulate Pol I transcription, indicating that SL1 recruitment of large T antigen to the rRNA promoter is required for Pol I activation.","method":"Immunoprecipitation in vitro and in vivo, in vitro transcription with T antigen deletion mutants, reconstituted transcription system","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1–2 — multiple binding assays combined with deletion mutagenesis and functional transcription reconstitution","pmids":["9203586"],"is_preprint":false},{"year":1999,"finding":"A kinase activity strongly associated with large T antigen phosphorylates the C-terminal activation domain of UBF, promoting the formation of a stable UBF-SL1 complex and rescuing the inability of dephosphorylated UBF to activate Pol I transcription.","method":"Cell labeling, in vitro kinase assay, co-immunoprecipitation, in vitro transcription reconstitution","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 — kinase assay with functional in vitro transcription reconstitution","pmids":["10082545"],"is_preprint":false},{"year":2005,"finding":"Human SL1 can direct accurate Pol I transcription in the absence of UBF and can interact with the rDNA promoter independently and stably; SL1 significantly reduces the rate of dissociation of UBF from rDNA, stabilizing UBF at the promoter; the rate of SL1 association with the promoter (rather than UBF) is the primary determinant of pre-initiation complex formation rate.","method":"In vitro transcription, DNase I footprinting, immobilized template assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro transcription and immobilized template assays with multiple mechanistic readouts","pmids":["15970593"],"is_preprint":false},{"year":2005,"finding":"PTEN represses Pol I transcription through disruption of the SL1 complex; PTEN induces dissociation of SL1 subunits and reduces SL1 occupancy on the rRNA gene promoter as shown by chromatin immunoprecipitation; PTEN-mediated repression requires its lipid phosphatase activity.","method":"ChIP assays, in vivo transcription measurement, siRNA knockdown, expression of constitutively active S6 kinase","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — ChIP and genetic epistasis (S6K rescue) with lipid phosphatase mutant, multiple orthogonal approaches","pmids":["16055704"],"is_preprint":false},{"year":2006,"finding":"CK2 kinase co-immunoprecipitates with the Pol I complex and is associated with the rRNA gene promoter; CK2 regulates the UBF-SL1 interaction by phosphorylating specific serines in the C-terminal domain of UBF, counteracting the inhibitory effect of HMG boxes 5 and 6; CK2 phosphorylation of UBF promotes multiple rounds of Pol I transcription re-initiation.","method":"Co-immunoprecipitation, ChIP, in vitro transcription with immobilized templates, inhibitor treatment","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 — ChIP plus co-IP plus immobilized template functional assays","pmids":["16971462"],"is_preprint":false},{"year":2007,"finding":"TAF(I)41 (encoded by MGC5306, now recognized as a novel SL1 subunit) co-purifies and co-immunoprecipitates with SL1; immunodepletion of TAFI41 dramatically reduces Pol I transcription; siRNA-mediated knockdown of TAFI41 causes loss of SL1 from the rDNA promoter in vivo and loss of Pol I from rDNA, with reduced pre-rRNA synthesis; addition of SL1 to TAFI41-depleted extracts restores transcription.","method":"Co-purification, co-immunoprecipitation, immunodepletion in vitro transcription, siRNA knockdown, ChIP","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (co-IP, immunodepletion, siRNA KD, ChIP) in single study","pmids":["17318177"],"is_preprint":false},{"year":2014,"finding":"Reconstitution of human Pol I transcription from the human rDNA promoter in mouse cells requires expression of all four human TAFI subunits of SL1; chimeric SL1 complexes containing human and mouse TAFIs can form but are inactive for human rDNA transcription, demonstrating that all four human TAFIs are necessary and sufficient for species-specific Pol I transcription.","method":"Novel in vivo transcription monitoring system (Pol I transcript with reporter amplified by influenza virus RNA polymerase), reconstitution in mouse cells, chimeric complex assembly","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 1 — functional reconstitution in cells with defined subunit combinations and novel reporter system","pmids":["24928901"],"is_preprint":false},{"year":2015,"finding":"The pSER domain of AF4 family proteins (component of the AEP coactivator) associates with SL1 on chromatin and loads TBP onto the TATA element to initiate RNA polymerase II-dependent transcription; MLL-AEP fusion proteins activate transcription initiation through SL1, revealing a role for SL1 as a TBP-loading factor in Pol II-dependent gene activation.","method":"ChIP, co-immunoprecipitation, in vitro transcription assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — ChIP and co-IP combined with functional transcription measurements","pmids":["26593443"],"is_preprint":false},{"year":2022,"finding":"Conditional deletion of the TAF1B subunit of SL1 causes a striking depletion of UBTF at both rDNA promoters but not elsewhere across rDNA; UBTF1 (but not UBTF2) cooperates with SL1 at rDNA promoters, and together they generate the specificity required for rDNA promoter recognition in vivo; the UBTF-E210K mutation reduces SL1 promoter recruitment and rDNA transcription.","method":"Conditional knockout of TAF1B, ChIP-seq, CRISPR knock-in of UBTF-E210K, cell-based Pol I transcription assays","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 2 — conditional KO with ChIP-seq and CRISPR knock-in, multiple orthogonal methods","pmids":["35139074"],"is_preprint":false},{"year":2015,"finding":"TAF1C frameshift mutations (within a mononucleotide repeat C8 in the coding sequence) occur in gastric cancers and colorectal cancers with high microsatellite instability, with intratumoral heterogeneity of these mutations, suggesting a role in tumorigenesis.","method":"SSCP and DNA sequencing of tumor samples","journal":"Pathology","confidence":"Low","confidence_rationale":"Tier 3 — mutation detection only, no direct functional/mechanistic assay","pmids":["25551296"],"is_preprint":false},{"year":2000,"finding":"Human TAF1C (TAF(I)110) gene is localized to chromosome 16q24 as a single copy; it is transcribed into multiple RNA species that could potentially produce variant isoforms of SL1 with different activation potentials.","method":"Somatic cell hybrid panel analysis, radiation hybrid panel analysis, FISH, Northern blot","journal":"Cytogenetics and cell genetics","confidence":"Low","confidence_rationale":"Tier 3 — genomic localization without direct functional mechanistic data on protein activity","pmids":["10894955"],"is_preprint":false},{"year":2020,"finding":"Homozygous TAF1C missense variants cause a severe early-onset neurological phenotype with global developmental delay; patient-derived fibroblasts show substantially reduced TAF1C mRNA and protein expression, implicating impaired Pol I transcription machinery in neurodegeneration.","method":"Patient fibroblast analysis, mRNA and protein quantification, clinical/MRI characterization","journal":"Clinical genetics","confidence":"Medium","confidence_rationale":"Tier 2–3 — patient-derived cell loss-of-function with protein expression measurement, but no reconstitution or direct mechanistic assay","pmids":["32779182"],"is_preprint":false},{"year":2025,"finding":"A novel homozygous missense variant (p.Ser589Leu) in TAF1C causes loss of nucleolar localization and formation of abnormal thread-like aggregates within the nucleoplasm, despite normal transcript and protein expression levels, demonstrating that proper subnuclear localization of TAF1C is required for normal neuronal function.","method":"Immunofluorescence analysis of patient cells, protein expression analysis, clinical phenotyping","journal":"Clinical genetics","confidence":"Medium","confidence_rationale":"Tier 2 — direct localization experiment in patient cells with clear mechanistic consequence (mislocalization with aggregation vs. functional loss)","pmids":["40371665"],"is_preprint":false},{"year":2025,"finding":"Mouse Taf1c variants (Taf1cR202Q, Taf1cS428A, Taf1c11bpdel) result in underrepresentation of homozygous mice at organogenesis stages, demonstrating that Taf1c is required for embryonic survival without causing craniofacial anomalies in surviving mice.","method":"CRISPR-Cas9 mouse knockin/deletion, allelic combination survival analysis","journal":"Developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO/KI mouse model with defined embryonic lethality phenotype","pmids":["40953792"],"is_preprint":false},{"year":2026,"finding":"TAF1C directly interacts with the H3K4 methyltransferase SETD1A to reprogram the epigenetic landscape by modulating H3K4me3, H3K27me3, and H3K27ac marks; TAF1C regulates enhancer and super-enhancer activities and increases ACSL4 expression, accelerating lipid synthesis and inducing ferroptosis in steatotic hepatocytes.","method":"Genome-wide CRISPR screen, ATAC-seq, co-immunoprecipitation (TAF1C-SETD1A), ChIP for histone marks, TAF1C knockdown/overexpression in vitro and in vivo","journal":"Journal of advanced research","confidence":"Medium","confidence_rationale":"Tier 2 — genome-wide screen plus co-IP and ChIP, but single study without independent replication","pmids":["42031105"],"is_preprint":false}],"current_model":"TAF1C (TAFI110/TAF(I)110) is the largest subunit of the RNA polymerase I-specific promoter selectivity factor SL1, a complex composed of TBP and three or four associated TAFIs that is necessary and sufficient for accurate rDNA transcription initiation; SL1 binds the rRNA gene promoter independently and stably, recruits and stabilizes UBF at the promoter through direct protein-protein interactions regulated by UBF phosphorylation (by CK2 and large T antigen-associated kinase), loads Pol I via hRRN3 interaction with TAFI110 and TAFI63, and is subject to reversible regulatory modifications including cdc2/cyclin B-mediated phosphorylation (silencing Pol I at mitosis), PCAF-mediated acetylation of TAFI68 (activating transcription), and disruption by tumor suppressors Rb and PTEN; proper nucleolar localization of TAF1C is essential for neuronal function, and TAF1C loss-of-function causes embryonic lethality in mice and a severe neurological syndrome in humans."},"narrative":{"teleology":[{"year":1988,"claim":"Establishing that Pol I transcription requires cooperative interaction between two factors — SL1 and UBF — at the rDNA promoter answered how promoter recognition occurs for Pol I, revealing that SL1 lacks autonomous DNA-binding specificity and instead relies on protein–protein contact with UBF.","evidence":"DNase I footprinting and in vitro transcription reconstitution with purified human factors","pmids":["3413483"],"confidence":"High","gaps":["Identity of individual SL1 subunits unknown","Nature of SL1–UBF contacts undefined"]},{"year":1992,"claim":"Purification and reconstitution of SL1 from TBP plus three novel TAFIs (110, 63, 48) resolved the molecular composition question and demonstrated that Pol I uses a distinct TBP–TAF complex analogous to TFIID for Pol II.","evidence":"Chromatographic purification, glycerol gradient sedimentation, antibody depletion, and reconstituted in vitro transcription","pmids":["1547496"],"confidence":"High","gaps":["Subunit stoichiometry not determined","Cloning and sequences of individual TAFIs not yet available"]},{"year":1994,"claim":"Demonstrating that each TAFI binds TBP independently and that TBP binding by SL1 TAFIs is mutually exclusive with TFIID TAFIIs established the principle that RNA polymerase selectivity arises from competition of distinct TAF sets for TBP, and that all four subunits are necessary and sufficient for transcription.","evidence":"Reconstitution with recombinant subunits, binding specificity assays, functional in vitro transcription","pmids":["7801123","7801130","8058785"],"confidence":"High","gaps":["Species-specificity determinants unknown","Post-translational regulation not explored"]},{"year":1996,"claim":"In vivo imaging showed SL1/TAF1C co-localizes with UBF and Pol I at nucleolar rDNA sites and remains associated with rDNA during mitosis, confirming the biochemical model in intact cells.","evidence":"Immunofluorescence microscopy, co-immunoprecipitation, actinomycin D treatment in HeLa cells","pmids":["8609157"],"confidence":"High","gaps":["Dynamics of SL1 loading/unloading in vivo unresolved","Contribution of individual TAFIs to localization not tested"]},{"year":1997,"claim":"Cloning of mouse TAFIs and assembly of chimeric human–mouse SL1 complexes showed that species-specific promoter selectivity arises from cumulative sequence differences among all TAFIs rather than a single subunit, and that SV40 large T antigen directly binds TAF1C, TAFI48, and TBP to activate Pol I transcription.","evidence":"cDNA cloning, chimeric complex reconstitution, in vitro transcription, co-IP with T-antigen mutants","pmids":["9050847","9203586"],"confidence":"High","gaps":["Structural basis of species selectivity undefined","How T antigen binding stimulates Pol I unknown"]},{"year":1998,"claim":"Identification of cdc2/cyclin B-mediated phosphorylation of TAF1C and TBP as the mechanism silencing Pol I at mitosis established a cell-cycle regulatory switch acting directly on the SL1 complex, disrupting its interaction with UBF.","evidence":"Phosphorylation assays, cell-free transcription with mitotic HeLa extracts, protein interaction studies","pmids":["9857193","9811537"],"confidence":"High","gaps":["Specific phosphorylation sites on TAF1C not mapped","Phosphatase responsible for reactivation not identified"]},{"year":1999,"claim":"Mapping UBF's C-terminal activation domain as the SL1-contact surface and showing that UBF phosphorylation (by CK2 and a T-antigen-associated kinase) is required for productive UBF–SL1 interaction explained how growth signals and viral oncoproteins converge on the SL1–UBF interface to regulate rDNA transcription.","evidence":"UBF deletion mutants, alkaline phosphatase treatment, kinase assays, in vitro transcription reconstitution","pmids":["10082553","10082545"],"confidence":"High","gaps":["Identity of CK2-specific UBF phosphosites confirmed later but structural detail of the contact lacking"]},{"year":2001,"claim":"Discovery that hRRN3 directly contacts TAF1C (TAFI110) and TAFI63 within SL1 to recruit initiation-competent Pol I to the promoter positioned SL1 as the essential bridge between Pol I loading and promoter recognition, while PCAF acetylation of TAFI68 provided an additional activating modification on SL1.","evidence":"Co-IP, in vitro interaction and transcription assays, acetyltransferase assays with PCAF and mSir2a","pmids":["11250903","11250901"],"confidence":"High","gaps":["Structural basis of hRRN3–SL1 interface unknown","Acetylation of TAFI68 validated only in vitro"]},{"year":2005,"claim":"Showing that SL1 can bind rDNA promoters and direct accurate transcription independently of UBF, while also stabilizing UBF at the promoter, revised the prevailing model: SL1 promoter association rate — not UBF — is the rate-limiting step in pre-initiation complex assembly. Concurrently, PTEN was found to repress Pol I by dissociating SL1 subunits from the promoter.","evidence":"Immobilized template assays, DNase I footprinting, in vitro transcription, ChIP with PTEN mutants and siRNA","pmids":["15970593","16055704"],"confidence":"High","gaps":["Mechanism by which PTEN dissociates SL1 not fully resolved","Whether PTEN acts directly on SL1 or via lipid signaling unclear"]},{"year":2007,"claim":"Identification of TAFI41 as a fourth essential SL1 subunit, whose depletion abolishes SL1 promoter occupancy and Pol I transcription in vivo, completed the subunit inventory of functional SL1.","evidence":"Co-purification, co-IP, immunodepletion, siRNA knockdown, ChIP","pmids":["17318177"],"confidence":"High","gaps":["TAFI41 contacts within the complex not mapped","Whether TAFI41 has regulatory modifications unknown"]},{"year":2014,"claim":"Demonstrating that all four human TAFIs are necessary and sufficient for species-specific Pol I transcription in mouse cells definitively resolved the species-selectivity problem as a property distributed across all SL1 subunits including TAF1C.","evidence":"Reconstitution of human Pol I transcription in mouse cells using a reporter amplified by influenza virus RNA polymerase","pmids":["24928901"],"confidence":"High","gaps":["Structural determinants of species selectivity still undefined at residue level"]},{"year":2015,"claim":"An unexpected role for SL1 in Pol II-dependent transcription emerged: AF4-family proteins recruit SL1 to load TBP onto TATA elements, and MLL–AEP fusions hijack this pathway, broadening SL1 function beyond Pol I.","evidence":"ChIP, co-IP, in vitro transcription assays in leukemia cell models","pmids":["26593443"],"confidence":"High","gaps":["Which TAFIs mediate AF4 contact not defined","Generality of SL1 in Pol II transcription beyond MLL targets unknown"]},{"year":2020,"claim":"Discovery that homozygous TAF1C missense variants cause a severe neurological syndrome in humans, with reduced TAF1C protein in patient fibroblasts, established TAF1C as a Mendelian disease gene and linked Pol I transcription machinery to neurodegeneration.","evidence":"Patient fibroblast analysis with mRNA/protein quantification, clinical and MRI characterization","pmids":["32779182"],"confidence":"Medium","gaps":["No reconstitution or rescue experiment performed","Whether rRNA synthesis is reduced in patient cells not directly measured","Mechanism of neuronal selectivity unknown"]},{"year":2025,"claim":"A TAF1C-p.Ser589Leu variant that mislocalizes from nucleoli to nucleoplasmic aggregates despite normal expression levels demonstrated that nucleolar targeting of TAF1C is essential for function, while mouse knockin models confirmed that Taf1c loss-of-function causes embryonic lethality.","evidence":"Immunofluorescence in patient cells; CRISPR-Cas9 mouse knockin/deletion with survival analysis","pmids":["40371665","40953792"],"confidence":"Medium","gaps":["Mislocalization mechanism (e.g. aggregation-prone sequence) not characterized","Tissue-specific requirements for TAF1C dosage not explored"]},{"year":2026,"claim":"A genome-wide CRISPR screen identified TAF1C as a direct interactor of the H3K4 methyltransferase SETD1A, through which it reprograms enhancer/super-enhancer activity and drives ACSL4-dependent ferroptosis in steatotic hepatocytes — an SL1-independent, chromatin-regulatory function.","evidence":"Genome-wide CRISPR screen, co-IP (TAF1C–SETD1A), ATAC-seq, ChIP for H3K4me3/H3K27me3/H3K27ac, knockdown/overexpression in vitro and in vivo","pmids":["42031105"],"confidence":"Medium","gaps":["Single study without independent replication","Whether this function requires other SL1 subunits or is TAF1C-autonomous not tested","Structural basis of TAF1C–SETD1A interaction unknown"]},{"year":null,"claim":"No high-resolution structure of the SL1 complex or of TAF1C exists; the precise cdc2/cyclin B phosphorylation sites on TAF1C, the structural basis of species-specific promoter selectivity at the residue level, the mechanism of PTEN-induced SL1 dissociation, and the basis for neuronal vulnerability to TAF1C loss remain open questions.","evidence":"","pmids":[],"confidence":"High","gaps":["No cryo-EM or crystal structure of SL1 or TAF1C","Phosphorylation sites on TAF1C not mapped","Neuronal selectivity mechanism unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[0,3,15,20]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[11,20]}],"localization":[{"term_id":"GO:0005730","term_label":"nucleolus","supporting_discovery_ids":[8,25]},{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[8]},{"term_id":"GO:0005654","term_label":"nucleoplasm","supporting_discovery_ids":[25]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,1,3,11,15]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[6,7]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[27]}],"complexes":["SL1 (TIF-IB)"],"partners":["TBP","TAF1B","TAF1A","TAF1D","RRN3","UBTF","SETD1A"],"other_free_text":[]},"mechanistic_narrative":"TAF1C (TAFI110) is the largest subunit of SL1 (selectivity factor 1), the TBP-containing complex that confers promoter selectivity on RNA polymerase I and is necessary and sufficient for accurate rDNA transcription initiation [PMID:1547496, PMID:7801130]. Within SL1, TAF1C binds TBP directly and interacts with each co-subunit (TAFI63, TAFI48, TAFI41) to form a stable complex that associates with the rDNA promoter independently of UBF, stabilizes UBF at the promoter through phosphorylation-dependent contacts, and loads Pol I via direct interaction of TAF1C and TAFI63 with hRRN3 [PMID:7801123, PMID:15970593, PMID:11250903]. TAF1C is a target of cdc2/cyclin B-mediated phosphorylation that silences Pol I transcription at mitosis, and SL1 integrity is further regulated by PTEN-induced dissociation and by tumor suppressor Rb disruption of the UBF–SL1 interface [PMID:9857193, PMID:16055704, PMID:11042686]. Homozygous loss-of-function or mislocalization variants in TAF1C cause a severe early-onset neurological syndrome in humans and embryonic lethality in mice [PMID:32779182, PMID:40371665, PMID:40953792]."},"prefetch_data":{"uniprot":{"accession":"Q15572","full_name":"TATA box-binding protein-associated factor RNA polymerase I subunit C","aliases":["RNA polymerase I-specific TBP-associated factor 110 kDa","TAFI110","TATA box-binding protein-associated factor 1C","TBP-associated factor 1C","Transcription initiation factor SL1/TIF-IB subunit C"],"length_aa":869,"mass_kda":95.2,"function":"Component of the transcription factor SL1/TIF-IB complex, which is involved in the assembly of the PIC (pre-initiation complex) during RNA polymerase I-dependent transcription. The rate of PIC formation probably is primarily dependent on the rate of association of SL1/TIF-IB with the rDNA promoter. SL1/TIF-IB is involved in stabilization of nucleolar transcription factor 1/UBTF on rDNA. Formation of SL1/TIF-IB excludes the association of TBP with TFIID subunits. 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SL-1 used for treatment of Cr(VI)-contaminated wastewater with waste molasses as carbon source.","date":"2024","source":"The Science of the total environment","url":"https://pubmed.ncbi.nlm.nih.gov/38340823","citation_count":3,"is_preprint":false},{"pmid":"32779182","id":"PMC_32779182","title":"Homozygous TAF1C variants are associated with a novel childhood-onset neurological phenotype.","date":"2020","source":"Clinical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/32779182","citation_count":3,"is_preprint":false},{"pmid":"12717718","id":"PMC_12717718","title":"Modeling the dynamics of the solvated SL1 domain of HIV-1 genomic RNA.","date":"2003","source":"Biopolymers","url":"https://pubmed.ncbi.nlm.nih.gov/12717718","citation_count":3,"is_preprint":false},{"pmid":"8789420","id":"PMC_8789420","title":"Mechanical and electrophysiological effects of a hydroxyphenyl-substituted tetrahydroisoquinoline, SL-1, on isolated rat cardiac tissues.","date":"1995","source":"Canadian journal of physiology and pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/8789420","citation_count":3,"is_preprint":false},{"pmid":"11259308","id":"PMC_11259308","title":"Solution structure of the SL1 RNA of the M1 double-stranded RNA virus of Saccharomyces cerevisiae.","date":"2001","source":"Biophysical journal","url":"https://pubmed.ncbi.nlm.nih.gov/11259308","citation_count":2,"is_preprint":false},{"pmid":"40305098","id":"PMC_40305098","title":"M. tuberculosis surface sulfoglycolipid SL-1 activates the mechanosensitive channel TRPV4 to enhance lysosomal biogenesis and exocytosis in macrophages.","date":"2025","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/40305098","citation_count":2,"is_preprint":false},{"pmid":"18008323","id":"PMC_18008323","title":"Insight into the intrinsic flexibility of the SL1 stem-loop from genomic RNA of HIV-1 as probed by molecular dynamics 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TRPV1-positive sensory neurons in a YM254890-reversible fashion.","date":"2025","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/40666927","citation_count":1,"is_preprint":false},{"pmid":"1213052","id":"PMC_1213052","title":"Invertase in cell-free culture fluids of Streptococcus mutans strain SL-1.","date":"1975","source":"Experientia","url":"https://pubmed.ncbi.nlm.nih.gov/1213052","citation_count":1,"is_preprint":false},{"pmid":"40758647","id":"PMC_40758647","title":"Targeting the SARS-CoV-2 RNA Translation Initiation Element SL1 by Molecules of Low Molecular Weight.","date":"2025","source":"Journal of the American Chemical Society","url":"https://pubmed.ncbi.nlm.nih.gov/40758647","citation_count":0,"is_preprint":false},{"pmid":"40953792","id":"PMC_40953792","title":"Mouse variants in Taf1c result in reduced survival to birth.","date":"2025","source":"Developmental 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aptamer","date":"2025-09-02","source":"bioRxiv","url":"https://doi.org/10.1101/2025.08.29.672993","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":45314,"output_tokens":6438,"usd":0.116256},"stage2":{"model":"claude-opus-4-6","input_tokens":10075,"output_tokens":3739,"usd":0.215775},"total_usd":0.332031,"stage1_batch_id":"msgbatch_01RPbVc9PDH9zQmYK5Hs6srm","stage2_batch_id":"msgbatch_01JVbVLzeKN2yVrsGp3zC8aM","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1992,\n      \"finding\": \"SL1 (selectivity factor 1) is a complex containing TBP (TATA-binding protein) and three distinct TBP-associated factors (TAFIs); purified TAFIs reconstituted with recombinant TBP complement SL1 activity, demonstrating that TBP plus novel associated factors are integral components of SL1 and are necessary for RNA polymerase I promoter selectivity.\",\n      \"method\": \"Column chromatography, glycerol gradient sedimentation, antibody depletion, reconstitution in vitro transcription\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution in vitro with purified components, replicated in multiple subsequent studies\",\n      \"pmids\": [\"1547496\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"SL1 has no sequence-specific DNA binding activity on its own, but cooperates with UBF1 through direct protein-protein interactions to form a complex at UCE and core promoter elements, enabling RNA polymerase I transcriptional activation.\",\n      \"method\": \"DNase I footprinting, in vitro transcription reconstitution, purification\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — DNase I footprinting and in vitro transcription reconstitution, foundational paper replicated extensively\",\n      \"pmids\": [\"3413483\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"The three TAFI subunits of SL1 (TAFI110, TAFI63, TAFI48) each bind individually and specifically to TBP; they also interact with each other to form a stable TBP-TAF complex. TBP binding by SL1 TAFIs is mutually exclusive with binding by TFIID subunits (TAFII250 and TAFII150), indicating that promoter- and RNA polymerase-selective TBP-TAF complexes are formed through mutually exclusive TBP binding.\",\n      \"method\": \"Subunit interaction assays, reconstitution, co-immunoprecipitation\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with recombinant subunits and binding specificity assays in a single rigorous study\",\n      \"pmids\": [\"7801123\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"In vivo and in vitro assembly of functional SL1 complexes from recombinant TAFIs (110, 63, 48) and TBP reconstitutes transcriptionally active SL1 that supports transcription from the human rRNA gene promoter; partial complexes without TBP do not efficiently direct transcription, demonstrating that all four subunits are necessary and sufficient.\",\n      \"method\": \"Reconstitution in vitro transcription, recombinant protein assembly\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — complete reconstitution with defined recombinant subunits and functional transcription assay\",\n      \"pmids\": [\"7801130\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"The conserved core domain of TBP alone (without the N-terminal domain) is sufficient to assemble functional SL1, and TBP directly interacts with the smallest SL1 subunit TAFI48, as shown by in vitro protein-protein interaction assay.\",\n      \"method\": \"Immunopurification of epitope-tagged TBP deletion mutants, in vitro protein-protein interaction assay, in vitro transcription\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — deletion mutagenesis with functional transcription readout and direct binding assay\",\n      \"pmids\": [\"8058785\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Mouse Pol I-specific TAFIs were cloned; human and mouse TAFI subunits can form stable chimeric complexes containing stoichiometric amounts of TBP and TAFIs, indicating conserved protein-protein contacts underlying SL1 assembly, while species-specific promoter selectivity results from cumulative subtle sequence differences among individual subunits.\",\n      \"method\": \"cDNA cloning, chimeric complex assembly, in vitro transcription\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution of chimeric complexes with functional transcription assay\",\n      \"pmids\": [\"9050847\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"SL1 is inactivated during mitosis by cdc2/cyclin B-directed phosphorylation of two subunits, TBP and hTAFI110 (TAF1C), and reactivated by dephosphorylation; mitotic phosphorylation impairs the interaction of SL1 with UBF, preventing pre-initiation complex formation and shutting down rDNA transcription at mitosis.\",\n      \"method\": \"Cell-free transcription reconstitution, phosphorylation assays, protein-protein interaction studies, mitotic HeLa cell extracts\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted cell-free system with biochemical phosphorylation assays and multiple orthogonal approaches\",\n      \"pmids\": [\"9857193\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Phosphorylation by cdc2/cyclin B inactivates SL1 (the TBP-containing factor) and abrogates Pol I transcription during mitosis; this provides a common mechanism for mitotic silencing of all three nuclear RNA polymerases via reversible inactivation of their respective TBP-TAF complexes.\",\n      \"method\": \"In vitro transcription in asynchronous vs. mitotic HeLa cell extracts, phosphorylation assays\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple approaches confirming cdc2/cyclin B phosphorylation inactivates SL1 in vitro\",\n      \"pmids\": [\"9811537\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"TBP/SL1 co-localizes with UBF and RNA polymerase I at sites of rRNA transcription in nucleoli of actively growing cells; during mitosis, TBP co-localizes with TAFIs (including TAF1C), UBF, and RNA polymerase I on chromosomal rRNA gene regions; anti-TBP antibodies co-immunoprecipitate TBP and TAFI63, confirming in vivo complex formation.\",\n      \"method\": \"Immunofluorescence microscopy, co-immunoprecipitation from cell extracts, actinomycin D treatment\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct localization by immunofluorescence combined with co-IP and functional perturbation\",\n      \"pmids\": [\"8609157\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The carboxy-terminal activation domain of UBF makes direct contact with the TBP-TAFI complex SL1; UBF phosphorylation at the C-terminus is required for SL1 interaction and recruitment to the rDNA promoter, as alkaline phosphatase treatment of UBF abolishes its ability to interact with SL1 and activate transcription.\",\n      \"method\": \"Protein-protein interaction assays with UBF deletion mutants, alkaline phosphatase treatment, DNase I footprinting, in vitro transcription\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal biochemical assays with defined deletion mutants and phosphatase treatment\",\n      \"pmids\": [\"10082553\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"PCAF acetylates TAF(I)68 (TAF1C), the second largest subunit of TIF-IB/SL1; acetylation by PCAF enhances binding of TAFI68 to the rDNA promoter and stimulates Pol I transcription; the NAD+-dependent deacetylase mSir2a deacetylates TAFI68 and represses Pol I transcription, demonstrating reversible acetylation as a regulatory mechanism.\",\n      \"method\": \"In vitro acetyltransferase assay, in vitro transcription reconstitution, promoter binding assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro acetylation assay with identified writer (PCAF) and eraser (mSir2a), functional transcription readout\",\n      \"pmids\": [\"11250901\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"hRRN3 interacts directly with TAF(I)110 and TAF(I)63 subunits of SL1; this interaction defines a transcriptionally competent subpopulation of Pol I (I beta); blocking the hRRN3-SL1 connection prevents recruitment of Pol I to the rDNA promoter, establishing hRRN3 as the factor linking initiation-competent Pol I to SL1.\",\n      \"method\": \"Co-immunoprecipitation, in vitro interaction assays, Pol I transcription assays, siRNA depletion\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP and functional transcription assays establishing pathway position\",\n      \"pmids\": [\"11250903\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Rb interacts directly with UBF (requiring a functional A/B pocket) but does not inhibit UBF binding to DNA; instead, the UBF-Rb complex blocks the interaction of UBF with SL1 (using the 48 kDa subunit as SL1 marker), thereby repressing RNA Pol I transcription; p130 but not p107 similarly associates with UBF and represses rDNA transcription.\",\n      \"method\": \"Direct protein interaction assays, DNase footprinting, band-shift assays, immunoprecipitation\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple direct binding assays, DNase footprinting, and functional transcription measurements\",\n      \"pmids\": [\"11042686\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"SV40 large T antigen directly binds SL1 in vitro and in SV40-infected cells; the interaction occurs with three SL1 subunits: TBP, TAFI48, and TAFI110; large T antigen mutants that cannot bind SL1 are unable to stimulate Pol I transcription, indicating that SL1 recruitment of large T antigen to the rRNA promoter is required for Pol I activation.\",\n      \"method\": \"Immunoprecipitation in vitro and in vivo, in vitro transcription with T antigen deletion mutants, reconstituted transcription system\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple binding assays combined with deletion mutagenesis and functional transcription reconstitution\",\n      \"pmids\": [\"9203586\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"A kinase activity strongly associated with large T antigen phosphorylates the C-terminal activation domain of UBF, promoting the formation of a stable UBF-SL1 complex and rescuing the inability of dephosphorylated UBF to activate Pol I transcription.\",\n      \"method\": \"Cell labeling, in vitro kinase assay, co-immunoprecipitation, in vitro transcription reconstitution\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — kinase assay with functional in vitro transcription reconstitution\",\n      \"pmids\": [\"10082545\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Human SL1 can direct accurate Pol I transcription in the absence of UBF and can interact with the rDNA promoter independently and stably; SL1 significantly reduces the rate of dissociation of UBF from rDNA, stabilizing UBF at the promoter; the rate of SL1 association with the promoter (rather than UBF) is the primary determinant of pre-initiation complex formation rate.\",\n      \"method\": \"In vitro transcription, DNase I footprinting, immobilized template assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro transcription and immobilized template assays with multiple mechanistic readouts\",\n      \"pmids\": [\"15970593\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"PTEN represses Pol I transcription through disruption of the SL1 complex; PTEN induces dissociation of SL1 subunits and reduces SL1 occupancy on the rRNA gene promoter as shown by chromatin immunoprecipitation; PTEN-mediated repression requires its lipid phosphatase activity.\",\n      \"method\": \"ChIP assays, in vivo transcription measurement, siRNA knockdown, expression of constitutively active S6 kinase\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP and genetic epistasis (S6K rescue) with lipid phosphatase mutant, multiple orthogonal approaches\",\n      \"pmids\": [\"16055704\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"CK2 kinase co-immunoprecipitates with the Pol I complex and is associated with the rRNA gene promoter; CK2 regulates the UBF-SL1 interaction by phosphorylating specific serines in the C-terminal domain of UBF, counteracting the inhibitory effect of HMG boxes 5 and 6; CK2 phosphorylation of UBF promotes multiple rounds of Pol I transcription re-initiation.\",\n      \"method\": \"Co-immunoprecipitation, ChIP, in vitro transcription with immobilized templates, inhibitor treatment\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP plus co-IP plus immobilized template functional assays\",\n      \"pmids\": [\"16971462\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"TAF(I)41 (encoded by MGC5306, now recognized as a novel SL1 subunit) co-purifies and co-immunoprecipitates with SL1; immunodepletion of TAFI41 dramatically reduces Pol I transcription; siRNA-mediated knockdown of TAFI41 causes loss of SL1 from the rDNA promoter in vivo and loss of Pol I from rDNA, with reduced pre-rRNA synthesis; addition of SL1 to TAFI41-depleted extracts restores transcription.\",\n      \"method\": \"Co-purification, co-immunoprecipitation, immunodepletion in vitro transcription, siRNA knockdown, ChIP\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (co-IP, immunodepletion, siRNA KD, ChIP) in single study\",\n      \"pmids\": [\"17318177\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Reconstitution of human Pol I transcription from the human rDNA promoter in mouse cells requires expression of all four human TAFI subunits of SL1; chimeric SL1 complexes containing human and mouse TAFIs can form but are inactive for human rDNA transcription, demonstrating that all four human TAFIs are necessary and sufficient for species-specific Pol I transcription.\",\n      \"method\": \"Novel in vivo transcription monitoring system (Pol I transcript with reporter amplified by influenza virus RNA polymerase), reconstitution in mouse cells, chimeric complex assembly\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — functional reconstitution in cells with defined subunit combinations and novel reporter system\",\n      \"pmids\": [\"24928901\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The pSER domain of AF4 family proteins (component of the AEP coactivator) associates with SL1 on chromatin and loads TBP onto the TATA element to initiate RNA polymerase II-dependent transcription; MLL-AEP fusion proteins activate transcription initiation through SL1, revealing a role for SL1 as a TBP-loading factor in Pol II-dependent gene activation.\",\n      \"method\": \"ChIP, co-immunoprecipitation, in vitro transcription assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP and co-IP combined with functional transcription measurements\",\n      \"pmids\": [\"26593443\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Conditional deletion of the TAF1B subunit of SL1 causes a striking depletion of UBTF at both rDNA promoters but not elsewhere across rDNA; UBTF1 (but not UBTF2) cooperates with SL1 at rDNA promoters, and together they generate the specificity required for rDNA promoter recognition in vivo; the UBTF-E210K mutation reduces SL1 promoter recruitment and rDNA transcription.\",\n      \"method\": \"Conditional knockout of TAF1B, ChIP-seq, CRISPR knock-in of UBTF-E210K, cell-based Pol I transcription assays\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with ChIP-seq and CRISPR knock-in, multiple orthogonal methods\",\n      \"pmids\": [\"35139074\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"TAF1C frameshift mutations (within a mononucleotide repeat C8 in the coding sequence) occur in gastric cancers and colorectal cancers with high microsatellite instability, with intratumoral heterogeneity of these mutations, suggesting a role in tumorigenesis.\",\n      \"method\": \"SSCP and DNA sequencing of tumor samples\",\n      \"journal\": \"Pathology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — mutation detection only, no direct functional/mechanistic assay\",\n      \"pmids\": [\"25551296\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Human TAF1C (TAF(I)110) gene is localized to chromosome 16q24 as a single copy; it is transcribed into multiple RNA species that could potentially produce variant isoforms of SL1 with different activation potentials.\",\n      \"method\": \"Somatic cell hybrid panel analysis, radiation hybrid panel analysis, FISH, Northern blot\",\n      \"journal\": \"Cytogenetics and cell genetics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — genomic localization without direct functional mechanistic data on protein activity\",\n      \"pmids\": [\"10894955\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Homozygous TAF1C missense variants cause a severe early-onset neurological phenotype with global developmental delay; patient-derived fibroblasts show substantially reduced TAF1C mRNA and protein expression, implicating impaired Pol I transcription machinery in neurodegeneration.\",\n      \"method\": \"Patient fibroblast analysis, mRNA and protein quantification, clinical/MRI characterization\",\n      \"journal\": \"Clinical genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — patient-derived cell loss-of-function with protein expression measurement, but no reconstitution or direct mechanistic assay\",\n      \"pmids\": [\"32779182\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A novel homozygous missense variant (p.Ser589Leu) in TAF1C causes loss of nucleolar localization and formation of abnormal thread-like aggregates within the nucleoplasm, despite normal transcript and protein expression levels, demonstrating that proper subnuclear localization of TAF1C is required for normal neuronal function.\",\n      \"method\": \"Immunofluorescence analysis of patient cells, protein expression analysis, clinical phenotyping\",\n      \"journal\": \"Clinical genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization experiment in patient cells with clear mechanistic consequence (mislocalization with aggregation vs. functional loss)\",\n      \"pmids\": [\"40371665\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Mouse Taf1c variants (Taf1cR202Q, Taf1cS428A, Taf1c11bpdel) result in underrepresentation of homozygous mice at organogenesis stages, demonstrating that Taf1c is required for embryonic survival without causing craniofacial anomalies in surviving mice.\",\n      \"method\": \"CRISPR-Cas9 mouse knockin/deletion, allelic combination survival analysis\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO/KI mouse model with defined embryonic lethality phenotype\",\n      \"pmids\": [\"40953792\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"TAF1C directly interacts with the H3K4 methyltransferase SETD1A to reprogram the epigenetic landscape by modulating H3K4me3, H3K27me3, and H3K27ac marks; TAF1C regulates enhancer and super-enhancer activities and increases ACSL4 expression, accelerating lipid synthesis and inducing ferroptosis in steatotic hepatocytes.\",\n      \"method\": \"Genome-wide CRISPR screen, ATAC-seq, co-immunoprecipitation (TAF1C-SETD1A), ChIP for histone marks, TAF1C knockdown/overexpression in vitro and in vivo\",\n      \"journal\": \"Journal of advanced research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genome-wide screen plus co-IP and ChIP, but single study without independent replication\",\n      \"pmids\": [\"42031105\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TAF1C (TAFI110/TAF(I)110) is the largest subunit of the RNA polymerase I-specific promoter selectivity factor SL1, a complex composed of TBP and three or four associated TAFIs that is necessary and sufficient for accurate rDNA transcription initiation; SL1 binds the rRNA gene promoter independently and stably, recruits and stabilizes UBF at the promoter through direct protein-protein interactions regulated by UBF phosphorylation (by CK2 and large T antigen-associated kinase), loads Pol I via hRRN3 interaction with TAFI110 and TAFI63, and is subject to reversible regulatory modifications including cdc2/cyclin B-mediated phosphorylation (silencing Pol I at mitosis), PCAF-mediated acetylation of TAFI68 (activating transcription), and disruption by tumor suppressors Rb and PTEN; proper nucleolar localization of TAF1C is essential for neuronal function, and TAF1C loss-of-function causes embryonic lethality in mice and a severe neurological syndrome in humans.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"TAF1C (TAFI110) is the largest subunit of SL1 (selectivity factor 1), the TBP-containing complex that confers promoter selectivity on RNA polymerase I and is necessary and sufficient for accurate rDNA transcription initiation [PMID:1547496, PMID:7801130]. Within SL1, TAF1C binds TBP directly and interacts with each co-subunit (TAFI63, TAFI48, TAFI41) to form a stable complex that associates with the rDNA promoter independently of UBF, stabilizes UBF at the promoter through phosphorylation-dependent contacts, and loads Pol I via direct interaction of TAF1C and TAFI63 with hRRN3 [PMID:7801123, PMID:15970593, PMID:11250903]. TAF1C is a target of cdc2/cyclin B-mediated phosphorylation that silences Pol I transcription at mitosis, and SL1 integrity is further regulated by PTEN-induced dissociation and by tumor suppressor Rb disruption of the UBF–SL1 interface [PMID:9857193, PMID:16055704, PMID:11042686]. Homozygous loss-of-function or mislocalization variants in TAF1C cause a severe early-onset neurological syndrome in humans and embryonic lethality in mice [PMID:32779182, PMID:40371665, PMID:40953792].\",\n  \"teleology\": [\n    {\n      \"year\": 1988,\n      \"claim\": \"Establishing that Pol I transcription requires cooperative interaction between two factors — SL1 and UBF — at the rDNA promoter answered how promoter recognition occurs for Pol I, revealing that SL1 lacks autonomous DNA-binding specificity and instead relies on protein–protein contact with UBF.\",\n      \"evidence\": \"DNase I footprinting and in vitro transcription reconstitution with purified human factors\",\n      \"pmids\": [\"3413483\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of individual SL1 subunits unknown\", \"Nature of SL1–UBF contacts undefined\"]\n    },\n    {\n      \"year\": 1992,\n      \"claim\": \"Purification and reconstitution of SL1 from TBP plus three novel TAFIs (110, 63, 48) resolved the molecular composition question and demonstrated that Pol I uses a distinct TBP–TAF complex analogous to TFIID for Pol II.\",\n      \"evidence\": \"Chromatographic purification, glycerol gradient sedimentation, antibody depletion, and reconstituted in vitro transcription\",\n      \"pmids\": [\"1547496\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Subunit stoichiometry not determined\", \"Cloning and sequences of individual TAFIs not yet available\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Demonstrating that each TAFI binds TBP independently and that TBP binding by SL1 TAFIs is mutually exclusive with TFIID TAFIIs established the principle that RNA polymerase selectivity arises from competition of distinct TAF sets for TBP, and that all four subunits are necessary and sufficient for transcription.\",\n      \"evidence\": \"Reconstitution with recombinant subunits, binding specificity assays, functional in vitro transcription\",\n      \"pmids\": [\"7801123\", \"7801130\", \"8058785\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Species-specificity determinants unknown\", \"Post-translational regulation not explored\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"In vivo imaging showed SL1/TAF1C co-localizes with UBF and Pol I at nucleolar rDNA sites and remains associated with rDNA during mitosis, confirming the biochemical model in intact cells.\",\n      \"evidence\": \"Immunofluorescence microscopy, co-immunoprecipitation, actinomycin D treatment in HeLa cells\",\n      \"pmids\": [\"8609157\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Dynamics of SL1 loading/unloading in vivo unresolved\", \"Contribution of individual TAFIs to localization not tested\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Cloning of mouse TAFIs and assembly of chimeric human–mouse SL1 complexes showed that species-specific promoter selectivity arises from cumulative sequence differences among all TAFIs rather than a single subunit, and that SV40 large T antigen directly binds TAF1C, TAFI48, and TBP to activate Pol I transcription.\",\n      \"evidence\": \"cDNA cloning, chimeric complex reconstitution, in vitro transcription, co-IP with T-antigen mutants\",\n      \"pmids\": [\"9050847\", \"9203586\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of species selectivity undefined\", \"How T antigen binding stimulates Pol I unknown\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Identification of cdc2/cyclin B-mediated phosphorylation of TAF1C and TBP as the mechanism silencing Pol I at mitosis established a cell-cycle regulatory switch acting directly on the SL1 complex, disrupting its interaction with UBF.\",\n      \"evidence\": \"Phosphorylation assays, cell-free transcription with mitotic HeLa extracts, protein interaction studies\",\n      \"pmids\": [\"9857193\", \"9811537\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific phosphorylation sites on TAF1C not mapped\", \"Phosphatase responsible for reactivation not identified\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Mapping UBF's C-terminal activation domain as the SL1-contact surface and showing that UBF phosphorylation (by CK2 and a T-antigen-associated kinase) is required for productive UBF–SL1 interaction explained how growth signals and viral oncoproteins converge on the SL1–UBF interface to regulate rDNA transcription.\",\n      \"evidence\": \"UBF deletion mutants, alkaline phosphatase treatment, kinase assays, in vitro transcription reconstitution\",\n      \"pmids\": [\"10082553\", \"10082545\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of CK2-specific UBF phosphosites confirmed later but structural detail of the contact lacking\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Discovery that hRRN3 directly contacts TAF1C (TAFI110) and TAFI63 within SL1 to recruit initiation-competent Pol I to the promoter positioned SL1 as the essential bridge between Pol I loading and promoter recognition, while PCAF acetylation of TAFI68 provided an additional activating modification on SL1.\",\n      \"evidence\": \"Co-IP, in vitro interaction and transcription assays, acetyltransferase assays with PCAF and mSir2a\",\n      \"pmids\": [\"11250903\", \"11250901\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of hRRN3–SL1 interface unknown\", \"Acetylation of TAFI68 validated only in vitro\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Showing that SL1 can bind rDNA promoters and direct accurate transcription independently of UBF, while also stabilizing UBF at the promoter, revised the prevailing model: SL1 promoter association rate — not UBF — is the rate-limiting step in pre-initiation complex assembly. Concurrently, PTEN was found to repress Pol I by dissociating SL1 subunits from the promoter.\",\n      \"evidence\": \"Immobilized template assays, DNase I footprinting, in vitro transcription, ChIP with PTEN mutants and siRNA\",\n      \"pmids\": [\"15970593\", \"16055704\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which PTEN dissociates SL1 not fully resolved\", \"Whether PTEN acts directly on SL1 or via lipid signaling unclear\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Identification of TAFI41 as a fourth essential SL1 subunit, whose depletion abolishes SL1 promoter occupancy and Pol I transcription in vivo, completed the subunit inventory of functional SL1.\",\n      \"evidence\": \"Co-purification, co-IP, immunodepletion, siRNA knockdown, ChIP\",\n      \"pmids\": [\"17318177\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"TAFI41 contacts within the complex not mapped\", \"Whether TAFI41 has regulatory modifications unknown\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Demonstrating that all four human TAFIs are necessary and sufficient for species-specific Pol I transcription in mouse cells definitively resolved the species-selectivity problem as a property distributed across all SL1 subunits including TAF1C.\",\n      \"evidence\": \"Reconstitution of human Pol I transcription in mouse cells using a reporter amplified by influenza virus RNA polymerase\",\n      \"pmids\": [\"24928901\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural determinants of species selectivity still undefined at residue level\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"An unexpected role for SL1 in Pol II-dependent transcription emerged: AF4-family proteins recruit SL1 to load TBP onto TATA elements, and MLL–AEP fusions hijack this pathway, broadening SL1 function beyond Pol I.\",\n      \"evidence\": \"ChIP, co-IP, in vitro transcription assays in leukemia cell models\",\n      \"pmids\": [\"26593443\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which TAFIs mediate AF4 contact not defined\", \"Generality of SL1 in Pol II transcription beyond MLL targets unknown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Discovery that homozygous TAF1C missense variants cause a severe neurological syndrome in humans, with reduced TAF1C protein in patient fibroblasts, established TAF1C as a Mendelian disease gene and linked Pol I transcription machinery to neurodegeneration.\",\n      \"evidence\": \"Patient fibroblast analysis with mRNA/protein quantification, clinical and MRI characterization\",\n      \"pmids\": [\"32779182\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No reconstitution or rescue experiment performed\", \"Whether rRNA synthesis is reduced in patient cells not directly measured\", \"Mechanism of neuronal selectivity unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A TAF1C-p.Ser589Leu variant that mislocalizes from nucleoli to nucleoplasmic aggregates despite normal expression levels demonstrated that nucleolar targeting of TAF1C is essential for function, while mouse knockin models confirmed that Taf1c loss-of-function causes embryonic lethality.\",\n      \"evidence\": \"Immunofluorescence in patient cells; CRISPR-Cas9 mouse knockin/deletion with survival analysis\",\n      \"pmids\": [\"40371665\", \"40953792\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mislocalization mechanism (e.g. aggregation-prone sequence) not characterized\", \"Tissue-specific requirements for TAF1C dosage not explored\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"A genome-wide CRISPR screen identified TAF1C as a direct interactor of the H3K4 methyltransferase SETD1A, through which it reprograms enhancer/super-enhancer activity and drives ACSL4-dependent ferroptosis in steatotic hepatocytes — an SL1-independent, chromatin-regulatory function.\",\n      \"evidence\": \"Genome-wide CRISPR screen, co-IP (TAF1C–SETD1A), ATAC-seq, ChIP for H3K4me3/H3K27me3/H3K27ac, knockdown/overexpression in vitro and in vivo\",\n      \"pmids\": [\"42031105\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single study without independent replication\", \"Whether this function requires other SL1 subunits or is TAF1C-autonomous not tested\", \"Structural basis of TAF1C–SETD1A interaction unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"No high-resolution structure of the SL1 complex or of TAF1C exists; the precise cdc2/cyclin B phosphorylation sites on TAF1C, the structural basis of species-specific promoter selectivity at the residue level, the mechanism of PTEN-induced SL1 dissociation, and the basis for neuronal vulnerability to TAF1C loss remain open questions.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No cryo-EM or crystal structure of SL1 or TAF1C\", \"Phosphorylation sites on TAF1C not mapped\", \"Neuronal selectivity mechanism unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 3, 15, 20]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [11, 20]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [8, 25]},\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [8]},\n      {\"term_id\": \"GO:0005654\", \"supporting_discovery_ids\": [25]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 1, 3, 11, 15]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [6, 7]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [27]}\n    ],\n    \"complexes\": [\n      \"SL1 (TIF-IB)\"\n    ],\n    \"partners\": [\n      \"TBP\",\n      \"TAF1B\",\n      \"TAF1A\",\n      \"TAF1D\",\n      \"RRN3\",\n      \"UBTF\",\n      \"SETD1A\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}