{"gene":"RRN3","run_date":"2026-04-28T20:42:06","timeline":{"discoveries":[{"year":1985,"finding":"TIF-IA (RRN3 mammalian homolog) is a growth-dependent transcription initiation factor that co-purifies with RNA polymerase I and is required for accurate and efficient rRNA transcription initiation in vitro; its amount or activity is absent in quiescent cells.","method":"Biochemical fractionation, in vitro transcription reconstitution","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with purified factor; foundational study replicated by subsequent work","pmids":["4070001"],"is_preprint":false},{"year":1990,"finding":"TIF-IA physically associates with RNA polymerase I, converting it into a transcriptionally active holoenzyme capable of specific rDNA promoter initiation; dephosphorylation of Pol I abolishes in vitro transcription initiation without affecting non-specific polymerizing activity.","method":"Biochemical co-purification, in vitro transcription, phosphatase treatment","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — in vitro biochemical reconstitution with multiple functional readouts","pmids":["2390974"],"is_preprint":false},{"year":1993,"finding":"TIF-IA is a 75 kDa monomeric polypeptide that interacts with RNA polymerase I; preinitiation complexes can form without TIF-IA but cannot initiate transcription (form first phosphodiester bonds) without it; after initiation, TIF-IA is liberated from the initiation complex.","method":"Purification, reconstituted transcription system with purified factors, template commitment assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 — reconstituted in vitro system with purified components","pmids":["8413268"],"is_preprint":false},{"year":1996,"finding":"Yeast Rrn3p is an essential RNA polymerase I transcription factor that interacts directly with Pol I independently of DNA template, stimulating Pol I recruitment to the promoter and formation of a Sarkosyl-resistant preinitiation complex; Rrn3p is not stably part of the preinitiation complex through multiple rounds of transcription.","method":"Immunoaffinity purification, in vitro transcription complementation, template commitment assays, single-round transcription with Sarkosyl","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — purified factor reconstitution with mechanistic assays in yeast","pmids":["8670901"],"is_preprint":false},{"year":1997,"finding":"Yeast Cbf5p genetically interacts with RRN3; RRN3 was identified as a multicopy suppressor of cbf5-1 temperature-sensitive mutant deficient in rRNA biosynthesis.","method":"Genetic suppressor screen, multicopy suppression","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis by suppressor screen in yeast","pmids":["9315678"],"is_preprint":false},{"year":2000,"finding":"Yeast Rrn3 interacts with Pol I subunit A43 to form a transcriptionally competent Pol I-Rrn3 complex; conditional mutations in A43 disrupt this complex, the two proteins form a stable complex when co-expressed in E. coli, overexpression of Rrn3 suppresses A43 mutant phenotype, and A43/Rrn3 mutants show synthetic lethality. Rrn3 also contacts the C-terminus of Rrn6 (core factor subunit), bridging Pol I to the core factor at the rDNA promoter.","method":"Genetic suppression, synthetic lethality, co-expression in E. coli, affinity chromatography, two-hybrid screen, immunoelectron microscopy","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods including reconstitution, genetics, and structural localization","pmids":["11032814"],"is_preprint":false},{"year":2000,"finding":"TIF-IA is the mammalian homolog of yeast Rrn3p; recombinant TIF-IA interacts with Pol I in the absence of template DNA, augments Pol I transcription in vivo, and rescues transcription in extracts from growth-arrested cells in vitro.","method":"Molecular cloning, sequence homology, in vitro transcription complementation, in vivo overexpression","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 1-2 — functional conservation demonstrated by in vitro and in vivo assays","pmids":["11265758"],"is_preprint":false},{"year":2000,"finding":"Human Rrn3 can rescue a yeast strain with disrupted RRN3 gene in vivo; a conserved point mutation compromises function in both yeast and human, confirming functional conservation.","method":"Yeast complementation assay, point mutagenesis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — functional rescue with mutagenesis validation","pmids":["10758157"],"is_preprint":false},{"year":2002,"finding":"TIF-IA interacts with Pol I subunits RPA43 and PAF67 via amino acids 512–609, and with TIF-IB/SL1 subunits TAF(I)95 and TAF(I)68 via a conserved LARAK motif (amino acids 411–415); nutrient starvation, density arrest, and protein synthesis inhibitors inactivate TIF-IA and impair its association with Pol I.","method":"Deletion mutant mapping, co-immunoprecipitation, in vitro interaction assays","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 1-2 — domain mapping with deletion mutants and multiple binding partner validations","pmids":["12393749"],"is_preprint":false},{"year":2002,"finding":"Phosphorylation state of Rrn3 regulates its interaction with the rpa43 subunit of RNA polymerase I; cycloheximide inhibits Rrn3 phosphorylation and causes dissociation from Pol I; dephosphorylated Rrn3 or bacterially-expressed Rrn3 (unphosphorylated) cannot restore transcription or interact with rpa43 in vitro.","method":"Co-immunoprecipitation in vivo, in vitro interaction assays with Sf9-expressed vs. E. coli-expressed Rrn3, transcription complementation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — biochemical assay with phosphorylation-dependent reconstitution","pmids":["12015311"],"is_preprint":false},{"year":2003,"finding":"Mammalian Rrn3 becomes inactivated (unable to form stable complex with Pol I) during the course of transcription; Rrn3 functions stoichiometrically rather than catalytically in rDNA transcription.","method":"In vitro transcription reactions, reuse assay of Rrn3 isolated post-transcription, co-immunoprecipitation","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro functional assays from single lab","pmids":["12646563"],"is_preprint":false},{"year":2003,"finding":"ERK and RSK kinases phosphorylate TIF-IA at Ser633 and Ser649; replacement of Ser649 with alanine inactivates TIF-IA, inhibits pre-rRNA synthesis, and retards cell growth, linking growth factor MAPK signaling to rDNA transcription.","method":"Phosphopeptide mapping, site-directed mutagenesis, in vivo rRNA synthesis assay, cell growth assay, kinase inhibitor (PD98059) treatment","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1-2 — phosphopeptide mapping combined with mutagenesis and multiple functional readouts","pmids":["12620228"],"is_preprint":false},{"year":2004,"finding":"mTOR signaling regulates Pol I transcription through TIF-IA; rapamycin-mediated mTOR inhibition causes hypophosphorylation of Ser44 (activating site) and hyperphosphorylation of Ser199 (inactivating site) of TIF-IA, impairs initiation complex formation, and causes TIF-IA translocation from nucleus to cytoplasm.","method":"Rapamycin treatment, phosphomutant analysis, transcription initiation complex assays, subcellular fractionation/localization","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods; replicated across multiple studies","pmids":["15004009"],"is_preprint":false},{"year":2005,"finding":"Genetic inactivation of TIF-IA leads to nucleolar disruption, cell cycle arrest, upregulation of p53 via increased binding of ribosomal protein L11 to MDM2 (reducing MDM2-p53 interaction), and p53-mediated apoptosis; RNAi-mediated loss of p53 rescues proliferation arrest.","method":"Homologous recombination knockout, Cre-mediated depletion in MEFs, co-immunoprecipitation (L11-MDM2), RNAi rescue, nucleolar morphology","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with mechanistic pathway placement and multiple orthogonal readouts","pmids":["15989966"],"is_preprint":false},{"year":2005,"finding":"JNK2 phosphorylates TIF-IA at Thr200 upon stress, impairing TIF-IA interaction with both Pol I and TIF-IB/SL1, thereby abrogating initiation complex formation and causing TIF-IA translocation from nucleolus to nucleoplasm; Thr200Val substitution or Jnk2 knockout prevents inactivation.","method":"Kinase assay, site-directed mutagenesis, co-immunoprecipitation, subcellular localization, Jnk2 knockout cells, initiation complex assay","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1-2 — kinase identification with mutagenesis and genetic confirmation in KO cells","pmids":["15805466"],"is_preprint":false},{"year":2007,"finding":"In Drosophila, TIF-IA (RRN3 ortholog) is required for rRNA synthesis and cell growth in vivo; TOR pathway regulates TIF-IA recruitment to rDNA, and TIF-IA overexpression can maintain rRNA transcription when TOR activity is reduced.","method":"Drosophila genetics (Tif-IA mutants), ChIP, epistasis with TOR pathway, overexpression rescue","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with multiple in vivo readouts in a multicellular model organism","pmids":["18086911"],"is_preprint":false},{"year":2007,"finding":"Pol I subunits Rpa34 and Rpa49 (yeast) regulate both the recruitment of Rrn3 to the rDNA promoter and its release during elongation; rpa49 mutants partially impair Rrn3 promoter recruitment (bypassed by N-terminal deletion of Rpa43) and strongly reduce release of Rrn3 during elongation.","method":"Yeast genetics, two-hybrid assay, ChIP, polymerase occupancy assay, drug sensitivity assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — genetic and ChIP-based epistasis in yeast with multiple mechanistic readouts","pmids":["18086878"],"is_preprint":false},{"year":2008,"finding":"CK2 phosphorylates TIF-IA at Ser170/172, triggering release of TIF-IA from the RPA43 subunit of Pol I after transcription initiation; blocking this phosphorylation (or tethering TIF-IA to RPA43) inhibits rDNA transcription elongation. FCP1 phosphatase dephosphorylates Ser170/172 to allow TIF-IA reassociation with Pol I for new transcription rounds.","method":"In vitro kinase assay, site-directed mutagenesis, FRAP, ChIP, co-immunoprecipitation, covalent tethering experiment","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods including kinase assay, mutagenesis, FRAP, and ChIP","pmids":["18559419"],"is_preprint":false},{"year":2008,"finding":"Rrn3 must be present during committed template complex formation for transcription to occur; the functional preinitiation complex (assembled with active Rrn3) is approximately 5-fold more resistant to heparin than the non-functional complex assembled without Rrn3, though Pol I can be recruited to template even without active Rrn3.","method":"Novel template recruitment assay (ChIP-like), heparin resistance assay, in vitro transcription","journal":"Gene expression","confidence":"Medium","confidence_rationale":"Tier 2 — biochemical assays from single lab with functional readouts","pmids":["18590050"],"is_preprint":false},{"year":2009,"finding":"TIF-IA rapidly shuttles between cytoplasm, nucleoplasm, and nucleolus with mean nucleolar residence time of ~30 s; upon ribotoxic stress (JNK2 activation), TIF-IA is released from nucleoli with a half-time of ~24 min, slower than its normal exchange rate, identifying JNK2 activation as the rate-limiting step for stress-induced relocalization.","method":"Live-cell fluorescence microscopy (FRAP), kinetic modeling, GFP-tagging, subcellular compartment analysis","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 — FRAP with kinetic modeling provides quantitative localization and dynamics data","pmids":["19450626"],"is_preprint":false},{"year":2011,"finding":"Crystal structure of Rrn3 reveals a unique HEAT repeat fold with a surface serine patch; phosphorylation of this serine patch represses human Pol I transcription; phospho-mimetic mutation prevents Rrn3 binding to Pol I in vitro, reduces cell growth and Pol I gene occupancy in vivo. Cross-linking shows Rrn3 binds between Pol I subcomplexes AC40/19 and A14/43.","method":"X-ray crystallography, cross-linking mass spectrometry, mutagenesis, in vitro binding assay, ChIP, cell growth assay","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with mutagenesis, in vitro binding, and in vivo validation","pmids":["21940764"],"is_preprint":false},{"year":2013,"finding":"Rrn3 is a DNA-binding protein; a domain (amino acids 382-400) with similarity to the HSF2 DNA-binding domain is essential for DNA binding; randomization or deletion of this domain abolishes DNA binding and abolishes rDNA transcription in vitro and yeast complementation, while preserving interactions with rpa43 and SL1.","method":"DNA binding assay, site-directed mutagenesis, in vitro transcription, yeast complementation, co-immunoprecipitation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — domain mutagenesis with multiple functional readouts including yeast complementation","pmids":["23393135"],"is_preprint":false},{"year":2013,"finding":"Activated Akt enhances rRNA synthesis by phosphorylating CK2α, which in turn phosphorylates TIF-IA; activated Akt also stabilizes TIF-IA protein, induces its translocation to the nucleolus, and enhances its interaction with Pol I.","method":"Co-immunoprecipitation, subcellular fractionation, kinase assays, pharmacological inhibitors (AZD8055, rapamycin), in vivo transcription assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 — multiple biochemical assays from single lab","pmids":["24297901"],"is_preprint":false},{"year":2014,"finding":"A 22 amino acid peptide within rpa43 is necessary and sufficient to mediate the rpa43-Rrn3 interaction interface; this peptide inhibits rDNA transcription in vitro and in cells, and blocks Pol I transcription and cell division.","method":"In silico analysis, in vitro transcription inhibition assay, cell transduction with TAT-coupled peptide, cell proliferation assay","journal":"Molecular cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro and cell-based validation of defined interaction domain","pmids":["25033839"],"is_preprint":false},{"year":2016,"finding":"Cryo-EM structure of the Pol I-Rrn3 complex at 4.8 Å resolution reveals how Rrn3 binding converts an inactive Pol I dimer into an initiation-competent monomeric complex.","method":"Cryo-electron microscopy structural determination","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM structure with mechanistic interpretation","pmids":["27418309"],"is_preprint":false},{"year":2016,"finding":"Heat shock inactivates TIF-IA by inhibiting CK2-dependent phosphorylation at Ser170/172; this is accompanied by upregulation of lncRNA PAPAS, which interacts with CHD4 (NuRD ATPase subunit) to deacetylate histones and reposition the promoter nucleosome to repress rDNA transcription.","method":"In vivo phosphorylation assay, RNAi knockdown, RNA-protein interaction assay, nucleosome positioning assay, ChIP","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods linking TIF-IA phosphorylation to chromatin and transcription","pmids":["27257073"],"is_preprint":false},{"year":2016,"finding":"LKB1 kinase activity promotes TIF-IA nuclear accumulation; in the presence of wild-type LKB1 (but not a kinase-dead mutant), TIF-IA quickly accumulates in the nucleus, maintaining pre-rRNA synthesis under AICAR-induced stress conditions.","method":"Cellular fractionation, wild-type vs. kinase-dead LKB1 expression, RNAi knockdown, TIF-IA phosphomutant analysis","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2-3 — kinase-dead comparison with subcellular fractionation, single lab","pmids":["26506235"],"is_preprint":false},{"year":2017,"finding":"ChIP-Seq after conditional inactivation of Rrn3 shows that preinitiation complex formation at rDNA is driven by UBF (UBTF) independently of transcription; loss of Rrn3 causes loss of Pol I from rDNA but an Enhancer Boundary Complex (CTCF/Cohesin) is stably maintained.","method":"High-resolution ChIP-Seq, conditional gene inactivation","journal":"PLoS genetics","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP-Seq with conditional KO; Rrn3 inactivation used as tool to define chromatin architecture","pmids":["28715449"],"is_preprint":false},{"year":2018,"finding":"TIF-IA degradation by specific NF-κB stress stimuli is dependent on UBF/p14ARF and Ser44 of TIF-IA, and precedes NF-κB activation; blocking TIF-IA degradation blocks stress effects on nucleolar size and NF-κB signaling, defining a TIF-IA-NF-κB nucleolar stress response pathway. CDK4 inhibition mimics TIF-IA degradation.","method":"RNAi knockdown, TIF-IA mutant (S44) analysis, CDK4 inhibitor treatment, co-immunoprecipitation, NF-κB reporter assay, ex vivo tissue analysis","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2-3 — multiple mechanistic assays but pathway partially defined, single lab","pmids":["29873780"],"is_preprint":false},{"year":2025,"finding":"Under nutrient deprivation, phosphorylation of RRN3 at Ser199 causes its translocation from nucleolus to nuclear plasma, where it regulates alternative polyadenylation (APA) of autophagy-related mRNAs (e.g., OPTN), enhancing their stability and promoting autophagy.","method":"Long-read RNA sequencing, PAR-CLIP, cellular fractionation, phosphomutant analysis, in vivo tumor xenograft","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 — multiple methods including PAR-CLIP and phosphomutant analysis from single lab","pmids":["41271632"],"is_preprint":false},{"year":2026,"finding":"In proliferating cells, TIF-IA binds to the cargo receptor p62 (SQSTM1); ATM activation during senescence disrupts this interaction, causing TIF-IA accumulation in the nucleus/nucleolus, which is essential for nucleolar phenotypic changes, SASP establishment, and increased ROS levels in senescence.","method":"Co-immunoprecipitation, ATM inhibition, multiple senescence models (OIS and TIS), mouse models, ROS measurement","journal":"Aging cell","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP with ATM-dependent mechanism validated in multiple models","pmids":["41466483"],"is_preprint":false},{"year":2026,"finding":"EGR1 activates RRN3 gene transcription by binding to the RRN3 promoter, and also directly interacts with Pol I transcription machinery components via its DNA-binding domain to enhance their recruitment to the rDNA promoter.","method":"ChIP, promoter reporter assay, co-immunoprecipitation, RNAi knockdown, in vivo tumor model","journal":"Communications biology","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP and co-IP from single lab","pmids":["41507426"],"is_preprint":false}],"current_model":"RRN3/TIF-IA is a conserved, growth-regulated RNA polymerase I initiation factor with a HEAT repeat fold that directly binds Pol I (via the A43/RPA43 subunit interface) and the core promoter factor (SL1/CF), bridging Pol I to the rDNA promoter; its activity is controlled by a phosphorylation code involving multiple kinases (ERK/RSK at S633/S649, mTOR-dependent S44, JNK2 at T200, CK2 at S170/172) and a phosphatase (FCP1), which regulate its association with Pol I, its nucleolar localization, and its release after initiation; it also has intrinsic DNA-binding activity essential for transcription, functions stoichiometrically (becoming inactivated after each round), and under stress conditions can redistribute to the nucleoplasm to regulate alternative polyadenylation of autophagy mRNAs."},"narrative":{"teleology":[{"year":1985,"claim":"Identification of TIF-IA as a growth-dependent factor required for Pol I transcription initiation established that rRNA synthesis is regulated at the level of a dissociable initiation factor whose activity is lost in quiescent cells.","evidence":"Biochemical fractionation and in vitro transcription reconstitution from mouse cell extracts","pmids":["4070001"],"confidence":"High","gaps":["Molecular identity of TIF-IA unknown","No phosphorylation data","Mechanism of growth regulation unresolved"]},{"year":1993,"claim":"Demonstration that TIF-IA is a 75 kDa monomer that associates with Pol I, is required for the first phosphodiester bond but not preinitiation complex assembly, and is released after initiation revealed its stoichiometric, single-use nature in transcription.","evidence":"Purified reconstituted transcription system with template commitment assays","pmids":["8413268","2390974"],"confidence":"High","gaps":["Gene identity not yet cloned","Mechanism of post-initiation release unknown","No structural information"]},{"year":1996,"claim":"Cloning of yeast RRN3 and demonstration that Rrn3p directly binds Pol I independently of DNA and stimulates promoter recruitment established RRN3 as the yeast counterpart of TIF-IA and a universal Pol I initiation factor.","evidence":"Immunoaffinity purification, in vitro transcription complementation, and Sarkosyl-resistant complex assays in yeast","pmids":["8670901"],"confidence":"High","gaps":["Mammalian gene not yet cloned","Binding interface on Pol I unresolved","Phospho-regulatory mechanism unknown"]},{"year":2000,"claim":"Identification of the RPA43 subunit as the direct Rrn3 binding partner on Pol I, and Rrn6 (core factor) as the promoter-side contact, established the bridging model whereby Rrn3 physically connects Pol I to the promoter-bound core factor; concurrent cloning of mammalian TIF-IA as the RRN3 homolog confirmed functional conservation across eukaryotes.","evidence":"Genetic suppression, synthetic lethality, co-expression in E. coli, two-hybrid, yeast complementation with human RRN3","pmids":["11032814","11265758","10758157"],"confidence":"High","gaps":["Detailed binding interface unresolved at atomic level","Phosphorylation sites not yet mapped in mammals","Mechanism of growth-dependent regulation still unclear"]},{"year":2002,"claim":"Mapping of TIF-IA interaction domains (aa 512–609 for Pol I, LARAK motif for SL1) and demonstration that phosphorylation state controls the Rrn3–Pol I interaction resolved how growth signals converge on TIF-IA at the molecular level.","evidence":"Deletion mutant mapping, co-immunoprecipitation, phosphatase treatment, comparison of phosphorylated vs. unphosphorylated recombinant Rrn3","pmids":["12393749","12015311"],"confidence":"High","gaps":["Specific kinases not yet identified","Stoichiometric versus catalytic action still debated","Structural basis of phospho-regulation unknown"]},{"year":2003,"claim":"Identification of ERK/RSK phosphorylation at Ser633/649 as activating modifications directly linked MAPK growth factor signaling to Pol I transcription via TIF-IA, while demonstration that Rrn3 functions stoichiometrically (becoming inactivated after each round) explained why its continual reactivation is required.","evidence":"Phosphopeptide mapping, site-directed mutagenesis, kinase inhibitor treatment, in vivo rRNA synthesis assays, post-transcription reuse assays","pmids":["12620228","12646563"],"confidence":"High","gaps":["Other regulatory kinases not yet identified","Mechanism of inactivation after initiation unclear","No structural data"]},{"year":2004,"claim":"Discovery that mTOR regulates TIF-IA via opposing phosphorylations at Ser44 (activating) and Ser199 (inactivating) established a second major signaling axis controlling Pol I transcription and showed that mTOR inhibition causes cytoplasmic translocation of TIF-IA.","evidence":"Rapamycin treatment, phosphomutant analysis, subcellular fractionation in mammalian cells","pmids":["15004009"],"confidence":"High","gaps":["Direct mTOR kinase activity on TIF-IA not demonstrated","Relationship between mTOR and ERK/RSK inputs unclear","In vivo physiological relevance in whole organism not tested"]},{"year":2005,"claim":"Identification of JNK2-mediated Thr200 phosphorylation as a stress-responsive inactivating modification that disrupts both Pol I and SL1 interactions, and genetic demonstration that TIF-IA loss activates p53 via the RPL11-MDM2 pathway, placed TIF-IA at the nexus of nucleolar stress sensing.","evidence":"JNK2 kinase assays, site-directed mutagenesis, Jnk2-KO cells, TIF-IA conditional knockout in MEFs, co-IP of L11-MDM2","pmids":["15805466","15989966"],"confidence":"High","gaps":["Whether JNK2 directly phosphorylates TIF-IA in vivo or acts through intermediary unclear","Full spectrum of stress signals converging on TIF-IA not mapped","Drosophila TOR-TIF-IA axis not yet confirmed"]},{"year":2007,"claim":"Conservation of TOR-dependent TIF-IA regulation in Drosophila and discovery that Pol I subunits Rpa34/Rpa49 regulate both Rrn3 recruitment and its post-initiation release broadened the mechanistic picture to include polymerase-intrinsic control of the Rrn3 cycle.","evidence":"Drosophila TIF-IA mutants with ChIP and TOR epistasis; yeast rpa49 mutant ChIP and polymerase occupancy assays","pmids":["18086911","18086878"],"confidence":"High","gaps":["Structural basis of Rpa49-mediated Rrn3 release unknown","Whether mammalian PAF53/CAST ortholog has equivalent role not tested"]},{"year":2008,"claim":"Identification of CK2-mediated Ser170/172 phosphorylation as the trigger for TIF-IA release from RPA43 after initiation, and FCP1 phosphatase as the recycling enzyme, completed the phosphorylation cycle model explaining how TIF-IA is used stoichiometrically yet continuously recycled.","evidence":"In vitro kinase assay, site-directed mutagenesis, FRAP, ChIP, covalent tethering of TIF-IA to RPA43","pmids":["18559419"],"confidence":"High","gaps":["Whether CK2 acts co-transcriptionally or post-initiation not resolved","Interplay between CK2 Ser170/172 and other phospho-sites unclear","Structural view of phospho-dependent release absent"]},{"year":2011,"claim":"The crystal structure of Rrn3 revealed a HEAT repeat fold with a surface serine patch whose phosphorylation blocks Pol I binding, providing the first atomic-level explanation for how phosphorylation acts as an on/off switch for Pol I initiation.","evidence":"X-ray crystallography, cross-linking mass spectrometry, phosphomimetic mutagenesis, ChIP, cell growth assays","pmids":["21940764"],"confidence":"High","gaps":["No structure of the Pol I–Rrn3 complex at this point","How the serine patch integrates signals from multiple kinases structurally unresolved"]},{"year":2013,"claim":"Discovery that Rrn3 possesses intrinsic DNA-binding activity via an HSF2-like domain (aa 382–400) essential for transcription but dispensable for Pol I/SL1 binding revealed a previously unsuspected direct contact with the rDNA template.","evidence":"DNA-binding assays, domain mutagenesis, in vitro transcription, yeast complementation","pmids":["23393135"],"confidence":"High","gaps":["Target DNA sequence specificity not defined","How DNA binding cooperates with Pol I/SL1 contacts structurally unknown","Whether DNA binding is regulated by phosphorylation untested"]},{"year":2016,"claim":"The cryo-EM structure of the Pol I–Rrn3 complex at 4.8 Å revealed that Rrn3 binding converts the inactive Pol I dimer into a monomeric initiation-competent form, providing the structural basis for the activation mechanism.","evidence":"Cryo-electron microscopy structural determination","pmids":["27418309"],"confidence":"High","gaps":["Resolution insufficient for side-chain detail at interface","Ternary complex with promoter factors and DNA not captured","Mechanism of dimer disruption not fully resolved"]},{"year":2025,"claim":"Discovery that Ser199-phosphorylated RRN3 translocates to the nucleoplasm under nutrient deprivation and regulates alternative polyadenylation of autophagy mRNAs (e.g., OPTN) established a non-canonical, Pol I-independent function in mRNA metabolism and autophagy.","evidence":"Long-read RNA sequencing, PAR-CLIP, cellular fractionation, phosphomutant analysis, in vivo tumor xenograft","pmids":["41271632"],"confidence":"Medium","gaps":["Mechanism of APA regulation (direct RNA binding vs. cofactor recruitment) not fully defined","Not independently replicated","Scope of target mRNAs beyond autophagy genes unclear"]},{"year":2026,"claim":"Identification of ATM-dependent disruption of the TIF-IA–SQSTM1/p62 interaction during senescence, leading to nuclear TIF-IA accumulation essential for SASP and nucleolar remodeling, extended TIF-IA function to senescence biology beyond its canonical Pol I role.","evidence":"Co-immunoprecipitation, ATM inhibition, oncogene- and therapy-induced senescence models, mouse models","pmids":["41466483"],"confidence":"Medium","gaps":["ATM phosphorylation site on TIF-IA or p62 not mapped","Whether nuclear TIF-IA drives senescence phenotypes through Pol I activity or other mechanisms unclear","Not independently replicated"]},{"year":null,"claim":"Key unresolved questions include how RRN3's DNA-binding, Pol I-bridging, and newly discovered mRNA-regulatory functions are coordinated; how the multisite phosphorylation code is integrated at the structural level; and whether non-canonical nucleoplasmic functions of RRN3 operate independently of its role in Pol I transcription.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution ternary complex structure with promoter DNA and SL1","Phosphorylation code integration across kinases not modeled structurally","Non-canonical mRNA regulatory mechanism needs independent replication and full target identification"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[21]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[0,2,3,6]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[1,5,17,24]}],"localization":[{"term_id":"GO:0005730","term_label":"nucleolus","supporting_discovery_ids":[19,22,30]},{"term_id":"GO:0005654","term_label":"nucleoplasm","supporting_discovery_ids":[14,19,29]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[12,19]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,2,3,5,6,11,17,24]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[11,12,14,22]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[29]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[13,14,25,28]}],"complexes":["Pol I–Rrn3 initiation complex"],"partners":["RPA43","POLR1A","TAF1A","TAF1B","SQSTM1","CTDP1","CSNK2A1"],"other_free_text":[]},"mechanistic_narrative":"RRN3 (TIF-IA) is a conserved, growth-regulated RNA polymerase I transcription initiation factor that bridges Pol I to the rDNA promoter and couples nutrient/growth factor signaling to ribosome biogenesis. It adopts a HEAT repeat fold and directly engages the Pol I subunit RPA43 (via a phosphorylation-dependent interface) and the promoter selectivity factor SL1/TIF-IB (via a LARAK motif), converting inactive Pol I dimers into initiation-competent monomers; it also possesses intrinsic DNA-binding activity essential for transcription and functions stoichiometrically, becoming inactivated after each initiation round through CK2-mediated phosphorylation at Ser170/172, with FCP1 phosphatase recycling it for subsequent rounds [PMID:8413268, PMID:20, PMID:18559419, PMID:23393135]. A multisite phosphorylation code integrates signals from ERK/RSK (Ser633/649), mTOR (Ser44/Ser199), JNK2 (Thr200), CK2, and Akt to control RRN3 activity, Pol I association, and nucleolar versus nucleoplasmic localization; genetic inactivation of RRN3 triggers nucleolar disruption, ribosomal protein L11-MDM2-dependent p53 stabilization, and apoptosis [PMID:12620228, PMID:15004009, PMID:15805466, PMID:15989966]. Beyond canonical Pol I transcription, nutrient deprivation-induced Ser199 phosphorylation relocates RRN3 to the nucleoplasm where it regulates alternative polyadenylation of autophagy mRNAs, and during senescence ATM-dependent disruption of its interaction with SQSTM1/p62 drives nucleolar remodeling and SASP establishment [PMID:41271632, PMID:41466483]."},"prefetch_data":{"uniprot":{"accession":"Q9NYV6","full_name":"RNA polymerase I-specific transcription initiation factor RRN3","aliases":["Transcription initiation factor IA","TIF-IA"],"length_aa":651,"mass_kda":74.1,"function":"Required for efficient transcription initiation by RNA polymerase I (Pol I). Required for the formation of the competent pre-initiation complex (PIC)","subcellular_location":"Nucleus, nucleolus","url":"https://www.uniprot.org/uniprotkb/Q9NYV6/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/RRN3","classification":"Common Essential","n_dependent_lines":380,"n_total_lines":380,"dependency_fraction":1.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/RRN3","total_profiled":1310},"omim":[{"mim_id":"621031","title":"POLYMERASE I, RNA, SUBUNIT E; POLR1E","url":"https://www.omim.org/entry/621031"},{"mim_id":"605121","title":"RRN3 HOMOLOG, RNA POLYMERASE I TRANSCRIPTION FACTOR; RRN3","url":"https://www.omim.org/entry/605121"},{"mim_id":"602896","title":"MITOGEN-ACTIVATED PROTEIN KINASE 9; MAPK9","url":"https://www.omim.org/entry/602896"},{"mim_id":"107325","title":"POLYMERASE I, RNA, SUBUNIT G; POLR1G","url":"https://www.omim.org/entry/107325"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoli rim","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/RRN3"},"hgnc":{"alias_symbol":["DKFZp566E104","TIF-IA"],"prev_symbol":[]},"alphafold":{"accession":"Q9NYV6","domains":[{"cath_id":"-","chopping":"398-564","consensus_level":"medium","plddt":86.3275,"start":398,"end":564},{"cath_id":"1.25.40","chopping":"52-163_175-209","consensus_level":"medium","plddt":89.5634,"start":52,"end":209}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NYV6","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NYV6-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NYV6-F1-predicted_aligned_error_v6.png","plddt_mean":77.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=RRN3","jax_strain_url":"https://www.jax.org/strain/search?query=RRN3"},"sequence":{"accession":"Q9NYV6","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9NYV6.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9NYV6/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NYV6"}},"corpus_meta":[{"pmid":"15004009","id":"PMC_15004009","title":"mTOR-dependent activation of the transcription factor TIF-IA links rRNA synthesis to nutrient availability.","date":"2004","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/15004009","citation_count":382,"is_preprint":false},{"pmid":"15989966","id":"PMC_15989966","title":"Genetic inactivation of the transcription factor TIF-IA leads to nucleolar disruption, cell cycle arrest, and p53-mediated apoptosis.","date":"2005","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/15989966","citation_count":219,"is_preprint":false},{"pmid":"12620228","id":"PMC_12620228","title":"ERK-dependent phosphorylation of the transcription initiation factor TIF-IA is required for RNA polymerase I transcription and cell growth.","date":"2003","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/12620228","citation_count":219,"is_preprint":false},{"pmid":"15805466","id":"PMC_15805466","title":"The nucleolus as a stress sensor: JNK2 inactivates the transcription factor TIF-IA and down-regulates rRNA synthesis.","date":"2005","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/15805466","citation_count":175,"is_preprint":false},{"pmid":"11032814","id":"PMC_11032814","title":"The recruitment of RNA polymerase I on rDNA is mediated by the interaction of the A43 subunit with Rrn3.","date":"2000","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/11032814","citation_count":146,"is_preprint":false},{"pmid":"2390974","id":"PMC_2390974","title":"A growth-dependent transcription initiation factor (TIF-IA) interacting with RNA polymerase I regulates mouse ribosomal RNA synthesis.","date":"1990","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/2390974","citation_count":114,"is_preprint":false},{"pmid":"11265758","id":"PMC_11265758","title":"TIF-IA, the factor mediating growth-dependent control of ribosomal RNA synthesis, is the mammalian homolog of yeast Rrn3p.","date":"2000","source":"EMBO reports","url":"https://pubmed.ncbi.nlm.nih.gov/11265758","citation_count":113,"is_preprint":false},{"pmid":"8670901","id":"PMC_8670901","title":"RRN3 gene of Saccharomyces cerevisiae encodes an essential RNA polymerase I transcription factor which interacts with the polymerase independently of DNA template.","date":"1996","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/8670901","citation_count":108,"is_preprint":false},{"pmid":"4070001","id":"PMC_4070001","title":"Growth-dependent regulation of rRNA synthesis is mediated by a transcription initiation factor (TIF-IA).","date":"1985","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/4070001","citation_count":94,"is_preprint":false},{"pmid":"9315678","id":"PMC_9315678","title":"The yeast nucleolar protein Cbf5p is involved in rRNA biosynthesis and interacts genetically with the RNA polymerase I transcription factor RRN3.","date":"1997","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/9315678","citation_count":92,"is_preprint":false},{"pmid":"10758157","id":"PMC_10758157","title":"RNA polymerase I transcription factor Rrn3 is functionally conserved between yeast and human.","date":"2000","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/10758157","citation_count":91,"is_preprint":false},{"pmid":"21940764","id":"PMC_21940764","title":"Molecular basis of Rrn3-regulated RNA polymerase I initiation and cell growth.","date":"2011","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/21940764","citation_count":88,"is_preprint":false},{"pmid":"18086911","id":"PMC_18086911","title":"Drosophila TIF-IA is required for ribosome synthesis and cell growth and is regulated by the TOR pathway.","date":"2007","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/18086911","citation_count":81,"is_preprint":false},{"pmid":"12393749","id":"PMC_12393749","title":"Multiple interactions between RNA polymerase I, TIF-IA and TAF(I) subunits regulate preinitiation complex assembly at the ribosomal gene promoter.","date":"2002","source":"EMBO reports","url":"https://pubmed.ncbi.nlm.nih.gov/12393749","citation_count":81,"is_preprint":false},{"pmid":"12015311","id":"PMC_12015311","title":"Rrn3 phosphorylation is a regulatory checkpoint for ribosome biogenesis.","date":"2002","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12015311","citation_count":75,"is_preprint":false},{"pmid":"18086878","id":"PMC_18086878","title":"Two RNA polymerase I subunits control the binding and release of Rrn3 during transcription.","date":"2007","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/18086878","citation_count":71,"is_preprint":false},{"pmid":"8413268","id":"PMC_8413268","title":"Function of the growth-regulated transcription initiation factor TIF-IA in initiation complex formation at the murine ribosomal gene promoter.","date":"1993","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/8413268","citation_count":70,"is_preprint":false},{"pmid":"18559419","id":"PMC_18559419","title":"Phosphorylation by casein kinase 2 facilitates rRNA gene transcription by promoting dissociation of TIF-IA from elongating RNA polymerase I.","date":"2008","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/18559419","citation_count":66,"is_preprint":false},{"pmid":"24297901","id":"PMC_24297901","title":"Akt activation enhances ribosomal RNA synthesis through casein kinase II and TIF-IA.","date":"2013","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/24297901","citation_count":65,"is_preprint":false},{"pmid":"28715449","id":"PMC_28715449","title":"A unique enhancer boundary complex on the mouse ribosomal RNA genes persists after loss of Rrn3 or UBF and the inactivation of RNA polymerase I transcription.","date":"2017","source":"PLoS genetics","url":"https://pubmed.ncbi.nlm.nih.gov/28715449","citation_count":63,"is_preprint":false},{"pmid":"27257073","id":"PMC_27257073","title":"Heat shock represses rRNA synthesis by inactivation of TIF-IA and lncRNA-dependent changes in nucleosome positioning.","date":"2016","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/27257073","citation_count":55,"is_preprint":false},{"pmid":"27418309","id":"PMC_27418309","title":"RNA polymerase I-Rrn3 complex at 4.8 Å resolution.","date":"2016","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/27418309","citation_count":54,"is_preprint":false},{"pmid":"23393135","id":"PMC_23393135","title":"DNA binding by the ribosomal DNA transcription factor rrn3 is essential for ribosomal DNA transcription.","date":"2013","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/23393135","citation_count":33,"is_preprint":false},{"pmid":"12646563","id":"PMC_12646563","title":"Rrn3 becomes inactivated in the process of ribosomal DNA transcription.","date":"2003","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12646563","citation_count":29,"is_preprint":false},{"pmid":"27641688","id":"PMC_27641688","title":"TIF-IA: An oncogenic target of pre-ribosomal RNA synthesis.","date":"2016","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/27641688","citation_count":22,"is_preprint":false},{"pmid":"29873780","id":"PMC_29873780","title":"Identification of a novel TIF-IA-NF-κB nucleolar stress response pathway.","date":"2018","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/29873780","citation_count":22,"is_preprint":false},{"pmid":"25356674","id":"PMC_25356674","title":"TIF-IA-dependent regulation of ribosome synthesis in drosophila muscle is required to maintain systemic insulin signaling and larval growth.","date":"2014","source":"PLoS genetics","url":"https://pubmed.ncbi.nlm.nih.gov/25356674","citation_count":22,"is_preprint":false},{"pmid":"25033839","id":"PMC_25033839","title":"Selective inhibition of rDNA transcription by a small-molecule peptide that targets the interface between RNA polymerase I and Rrn3.","date":"2014","source":"Molecular cancer research : MCR","url":"https://pubmed.ncbi.nlm.nih.gov/25033839","citation_count":20,"is_preprint":false},{"pmid":"18590050","id":"PMC_18590050","title":"Mammalian Rrn3 is required for the formation of a transcription competent preinitiation complex containing RNA polymerase I.","date":"2008","source":"Gene expression","url":"https://pubmed.ncbi.nlm.nih.gov/18590050","citation_count":20,"is_preprint":false},{"pmid":"18047649","id":"PMC_18047649","title":"Biased exonization of transposed elements in duplicated genes: A lesson from the TIF-IA gene.","date":"2007","source":"BMC molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/18047649","citation_count":19,"is_preprint":false},{"pmid":"19450626","id":"PMC_19450626","title":"Dynamic subcellular partitioning of the nucleolar transcription factor TIF-IA under ribotoxic stress.","date":"2009","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/19450626","citation_count":13,"is_preprint":false},{"pmid":"26506235","id":"PMC_26506235","title":"LKB1 promotes cell survival by modulating TIF-IA-mediated pre-ribosomal RNA synthesis under uridine downregulated conditions.","date":"2016","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/26506235","citation_count":9,"is_preprint":false},{"pmid":"35006303","id":"PMC_35006303","title":"Rrn3 gene knockout affects ethanol-induced locomotion in adult heterozygous zebrafish.","date":"2022","source":"Psychopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/35006303","citation_count":4,"is_preprint":false},{"pmid":"25883228","id":"PMC_25883228","title":"TIF-IA and Ebp1 regulate RNA synthesis in T cells.","date":"2015","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/25883228","citation_count":2,"is_preprint":false},{"pmid":"16358415","id":"PMC_16358415","title":"The association of TIF-IA and polymerase I mediates promoter recruitment and regulation of ribosomal RNA transcription in Acanthamoeba castellanii.","date":"2005","source":"Gene expression","url":"https://pubmed.ncbi.nlm.nih.gov/16358415","citation_count":1,"is_preprint":false},{"pmid":"41271632","id":"PMC_41271632","title":"Nutrient stress diverts RRN3 from rRNA transcription to alternative polyadenylation of autophagy mRNAs in ovarian cancer.","date":"2025","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/41271632","citation_count":0,"is_preprint":false},{"pmid":"41116164","id":"PMC_41116164","title":"NSH76: a selective inhibitor of RRN3 and RNA polymerase I transcription with potential for cancer therapy.","date":"2025","source":"Journal of translational medicine","url":"https://pubmed.ncbi.nlm.nih.gov/41116164","citation_count":0,"is_preprint":false},{"pmid":"41466483","id":"PMC_41466483","title":"Loss of p62 Binding Allows TIF-IA Accumulation in Senescence, Which Promotes Phenotypic Changes to Nucleoli and the Senescence Associated Secretory Phenotype.","date":"2026","source":"Aging cell","url":"https://pubmed.ncbi.nlm.nih.gov/41466483","citation_count":0,"is_preprint":false},{"pmid":"41507426","id":"PMC_41507426","title":"Early growth response 1 promotes RNA polymerase I-directed transcription and cancer growth by activating RRN3 expression.","date":"2026","source":"Communications biology","url":"https://pubmed.ncbi.nlm.nih.gov/41507426","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2024.10.30.621142","title":"Determinants of transcription initiation efficiency and start site selection by RNA polymerase I","date":"2024-10-30","source":"bioRxiv","url":"https://doi.org/10.1101/2024.10.30.621142","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":18523,"output_tokens":6997,"usd":0.080262},"stage2":{"model":"claude-opus-4-6","input_tokens":10729,"output_tokens":4120,"usd":0.234967},"total_usd":0.315229,"stage1_batch_id":"msgbatch_011rkcQdVV1RaFq9XhcG6df6","stage2_batch_id":"msgbatch_01RzgrJafdF4EWHhj5mNi6dh","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1985,\n      \"finding\": \"TIF-IA (RRN3 mammalian homolog) is a growth-dependent transcription initiation factor that co-purifies with RNA polymerase I and is required for accurate and efficient rRNA transcription initiation in vitro; its amount or activity is absent in quiescent cells.\",\n      \"method\": \"Biochemical fractionation, in vitro transcription reconstitution\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with purified factor; foundational study replicated by subsequent work\",\n      \"pmids\": [\"4070001\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"TIF-IA physically associates with RNA polymerase I, converting it into a transcriptionally active holoenzyme capable of specific rDNA promoter initiation; dephosphorylation of Pol I abolishes in vitro transcription initiation without affecting non-specific polymerizing activity.\",\n      \"method\": \"Biochemical co-purification, in vitro transcription, phosphatase treatment\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro biochemical reconstitution with multiple functional readouts\",\n      \"pmids\": [\"2390974\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"TIF-IA is a 75 kDa monomeric polypeptide that interacts with RNA polymerase I; preinitiation complexes can form without TIF-IA but cannot initiate transcription (form first phosphodiester bonds) without it; after initiation, TIF-IA is liberated from the initiation complex.\",\n      \"method\": \"Purification, reconstituted transcription system with purified factors, template commitment assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro system with purified components\",\n      \"pmids\": [\"8413268\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Yeast Rrn3p is an essential RNA polymerase I transcription factor that interacts directly with Pol I independently of DNA template, stimulating Pol I recruitment to the promoter and formation of a Sarkosyl-resistant preinitiation complex; Rrn3p is not stably part of the preinitiation complex through multiple rounds of transcription.\",\n      \"method\": \"Immunoaffinity purification, in vitro transcription complementation, template commitment assays, single-round transcription with Sarkosyl\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — purified factor reconstitution with mechanistic assays in yeast\",\n      \"pmids\": [\"8670901\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Yeast Cbf5p genetically interacts with RRN3; RRN3 was identified as a multicopy suppressor of cbf5-1 temperature-sensitive mutant deficient in rRNA biosynthesis.\",\n      \"method\": \"Genetic suppressor screen, multicopy suppression\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis by suppressor screen in yeast\",\n      \"pmids\": [\"9315678\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Yeast Rrn3 interacts with Pol I subunit A43 to form a transcriptionally competent Pol I-Rrn3 complex; conditional mutations in A43 disrupt this complex, the two proteins form a stable complex when co-expressed in E. coli, overexpression of Rrn3 suppresses A43 mutant phenotype, and A43/Rrn3 mutants show synthetic lethality. Rrn3 also contacts the C-terminus of Rrn6 (core factor subunit), bridging Pol I to the core factor at the rDNA promoter.\",\n      \"method\": \"Genetic suppression, synthetic lethality, co-expression in E. coli, affinity chromatography, two-hybrid screen, immunoelectron microscopy\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including reconstitution, genetics, and structural localization\",\n      \"pmids\": [\"11032814\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"TIF-IA is the mammalian homolog of yeast Rrn3p; recombinant TIF-IA interacts with Pol I in the absence of template DNA, augments Pol I transcription in vivo, and rescues transcription in extracts from growth-arrested cells in vitro.\",\n      \"method\": \"Molecular cloning, sequence homology, in vitro transcription complementation, in vivo overexpression\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — functional conservation demonstrated by in vitro and in vivo assays\",\n      \"pmids\": [\"11265758\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Human Rrn3 can rescue a yeast strain with disrupted RRN3 gene in vivo; a conserved point mutation compromises function in both yeast and human, confirming functional conservation.\",\n      \"method\": \"Yeast complementation assay, point mutagenesis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional rescue with mutagenesis validation\",\n      \"pmids\": [\"10758157\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"TIF-IA interacts with Pol I subunits RPA43 and PAF67 via amino acids 512–609, and with TIF-IB/SL1 subunits TAF(I)95 and TAF(I)68 via a conserved LARAK motif (amino acids 411–415); nutrient starvation, density arrest, and protein synthesis inhibitors inactivate TIF-IA and impair its association with Pol I.\",\n      \"method\": \"Deletion mutant mapping, co-immunoprecipitation, in vitro interaction assays\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — domain mapping with deletion mutants and multiple binding partner validations\",\n      \"pmids\": [\"12393749\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Phosphorylation state of Rrn3 regulates its interaction with the rpa43 subunit of RNA polymerase I; cycloheximide inhibits Rrn3 phosphorylation and causes dissociation from Pol I; dephosphorylated Rrn3 or bacterially-expressed Rrn3 (unphosphorylated) cannot restore transcription or interact with rpa43 in vitro.\",\n      \"method\": \"Co-immunoprecipitation in vivo, in vitro interaction assays with Sf9-expressed vs. E. coli-expressed Rrn3, transcription complementation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — biochemical assay with phosphorylation-dependent reconstitution\",\n      \"pmids\": [\"12015311\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Mammalian Rrn3 becomes inactivated (unable to form stable complex with Pol I) during the course of transcription; Rrn3 functions stoichiometrically rather than catalytically in rDNA transcription.\",\n      \"method\": \"In vitro transcription reactions, reuse assay of Rrn3 isolated post-transcription, co-immunoprecipitation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro functional assays from single lab\",\n      \"pmids\": [\"12646563\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"ERK and RSK kinases phosphorylate TIF-IA at Ser633 and Ser649; replacement of Ser649 with alanine inactivates TIF-IA, inhibits pre-rRNA synthesis, and retards cell growth, linking growth factor MAPK signaling to rDNA transcription.\",\n      \"method\": \"Phosphopeptide mapping, site-directed mutagenesis, in vivo rRNA synthesis assay, cell growth assay, kinase inhibitor (PD98059) treatment\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — phosphopeptide mapping combined with mutagenesis and multiple functional readouts\",\n      \"pmids\": [\"12620228\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"mTOR signaling regulates Pol I transcription through TIF-IA; rapamycin-mediated mTOR inhibition causes hypophosphorylation of Ser44 (activating site) and hyperphosphorylation of Ser199 (inactivating site) of TIF-IA, impairs initiation complex formation, and causes TIF-IA translocation from nucleus to cytoplasm.\",\n      \"method\": \"Rapamycin treatment, phosphomutant analysis, transcription initiation complex assays, subcellular fractionation/localization\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods; replicated across multiple studies\",\n      \"pmids\": [\"15004009\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Genetic inactivation of TIF-IA leads to nucleolar disruption, cell cycle arrest, upregulation of p53 via increased binding of ribosomal protein L11 to MDM2 (reducing MDM2-p53 interaction), and p53-mediated apoptosis; RNAi-mediated loss of p53 rescues proliferation arrest.\",\n      \"method\": \"Homologous recombination knockout, Cre-mediated depletion in MEFs, co-immunoprecipitation (L11-MDM2), RNAi rescue, nucleolar morphology\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with mechanistic pathway placement and multiple orthogonal readouts\",\n      \"pmids\": [\"15989966\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"JNK2 phosphorylates TIF-IA at Thr200 upon stress, impairing TIF-IA interaction with both Pol I and TIF-IB/SL1, thereby abrogating initiation complex formation and causing TIF-IA translocation from nucleolus to nucleoplasm; Thr200Val substitution or Jnk2 knockout prevents inactivation.\",\n      \"method\": \"Kinase assay, site-directed mutagenesis, co-immunoprecipitation, subcellular localization, Jnk2 knockout cells, initiation complex assay\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — kinase identification with mutagenesis and genetic confirmation in KO cells\",\n      \"pmids\": [\"15805466\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"In Drosophila, TIF-IA (RRN3 ortholog) is required for rRNA synthesis and cell growth in vivo; TOR pathway regulates TIF-IA recruitment to rDNA, and TIF-IA overexpression can maintain rRNA transcription when TOR activity is reduced.\",\n      \"method\": \"Drosophila genetics (Tif-IA mutants), ChIP, epistasis with TOR pathway, overexpression rescue\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with multiple in vivo readouts in a multicellular model organism\",\n      \"pmids\": [\"18086911\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Pol I subunits Rpa34 and Rpa49 (yeast) regulate both the recruitment of Rrn3 to the rDNA promoter and its release during elongation; rpa49 mutants partially impair Rrn3 promoter recruitment (bypassed by N-terminal deletion of Rpa43) and strongly reduce release of Rrn3 during elongation.\",\n      \"method\": \"Yeast genetics, two-hybrid assay, ChIP, polymerase occupancy assay, drug sensitivity assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic and ChIP-based epistasis in yeast with multiple mechanistic readouts\",\n      \"pmids\": [\"18086878\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"CK2 phosphorylates TIF-IA at Ser170/172, triggering release of TIF-IA from the RPA43 subunit of Pol I after transcription initiation; blocking this phosphorylation (or tethering TIF-IA to RPA43) inhibits rDNA transcription elongation. FCP1 phosphatase dephosphorylates Ser170/172 to allow TIF-IA reassociation with Pol I for new transcription rounds.\",\n      \"method\": \"In vitro kinase assay, site-directed mutagenesis, FRAP, ChIP, co-immunoprecipitation, covalent tethering experiment\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including kinase assay, mutagenesis, FRAP, and ChIP\",\n      \"pmids\": [\"18559419\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Rrn3 must be present during committed template complex formation for transcription to occur; the functional preinitiation complex (assembled with active Rrn3) is approximately 5-fold more resistant to heparin than the non-functional complex assembled without Rrn3, though Pol I can be recruited to template even without active Rrn3.\",\n      \"method\": \"Novel template recruitment assay (ChIP-like), heparin resistance assay, in vitro transcription\",\n      \"journal\": \"Gene expression\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — biochemical assays from single lab with functional readouts\",\n      \"pmids\": [\"18590050\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"TIF-IA rapidly shuttles between cytoplasm, nucleoplasm, and nucleolus with mean nucleolar residence time of ~30 s; upon ribotoxic stress (JNK2 activation), TIF-IA is released from nucleoli with a half-time of ~24 min, slower than its normal exchange rate, identifying JNK2 activation as the rate-limiting step for stress-induced relocalization.\",\n      \"method\": \"Live-cell fluorescence microscopy (FRAP), kinetic modeling, GFP-tagging, subcellular compartment analysis\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — FRAP with kinetic modeling provides quantitative localization and dynamics data\",\n      \"pmids\": [\"19450626\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Crystal structure of Rrn3 reveals a unique HEAT repeat fold with a surface serine patch; phosphorylation of this serine patch represses human Pol I transcription; phospho-mimetic mutation prevents Rrn3 binding to Pol I in vitro, reduces cell growth and Pol I gene occupancy in vivo. Cross-linking shows Rrn3 binds between Pol I subcomplexes AC40/19 and A14/43.\",\n      \"method\": \"X-ray crystallography, cross-linking mass spectrometry, mutagenesis, in vitro binding assay, ChIP, cell growth assay\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with mutagenesis, in vitro binding, and in vivo validation\",\n      \"pmids\": [\"21940764\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Rrn3 is a DNA-binding protein; a domain (amino acids 382-400) with similarity to the HSF2 DNA-binding domain is essential for DNA binding; randomization or deletion of this domain abolishes DNA binding and abolishes rDNA transcription in vitro and yeast complementation, while preserving interactions with rpa43 and SL1.\",\n      \"method\": \"DNA binding assay, site-directed mutagenesis, in vitro transcription, yeast complementation, co-immunoprecipitation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — domain mutagenesis with multiple functional readouts including yeast complementation\",\n      \"pmids\": [\"23393135\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Activated Akt enhances rRNA synthesis by phosphorylating CK2α, which in turn phosphorylates TIF-IA; activated Akt also stabilizes TIF-IA protein, induces its translocation to the nucleolus, and enhances its interaction with Pol I.\",\n      \"method\": \"Co-immunoprecipitation, subcellular fractionation, kinase assays, pharmacological inhibitors (AZD8055, rapamycin), in vivo transcription assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple biochemical assays from single lab\",\n      \"pmids\": [\"24297901\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"A 22 amino acid peptide within rpa43 is necessary and sufficient to mediate the rpa43-Rrn3 interaction interface; this peptide inhibits rDNA transcription in vitro and in cells, and blocks Pol I transcription and cell division.\",\n      \"method\": \"In silico analysis, in vitro transcription inhibition assay, cell transduction with TAT-coupled peptide, cell proliferation assay\",\n      \"journal\": \"Molecular cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro and cell-based validation of defined interaction domain\",\n      \"pmids\": [\"25033839\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Cryo-EM structure of the Pol I-Rrn3 complex at 4.8 Å resolution reveals how Rrn3 binding converts an inactive Pol I dimer into an initiation-competent monomeric complex.\",\n      \"method\": \"Cryo-electron microscopy structural determination\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structure with mechanistic interpretation\",\n      \"pmids\": [\"27418309\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Heat shock inactivates TIF-IA by inhibiting CK2-dependent phosphorylation at Ser170/172; this is accompanied by upregulation of lncRNA PAPAS, which interacts with CHD4 (NuRD ATPase subunit) to deacetylate histones and reposition the promoter nucleosome to repress rDNA transcription.\",\n      \"method\": \"In vivo phosphorylation assay, RNAi knockdown, RNA-protein interaction assay, nucleosome positioning assay, ChIP\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods linking TIF-IA phosphorylation to chromatin and transcription\",\n      \"pmids\": [\"27257073\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"LKB1 kinase activity promotes TIF-IA nuclear accumulation; in the presence of wild-type LKB1 (but not a kinase-dead mutant), TIF-IA quickly accumulates in the nucleus, maintaining pre-rRNA synthesis under AICAR-induced stress conditions.\",\n      \"method\": \"Cellular fractionation, wild-type vs. kinase-dead LKB1 expression, RNAi knockdown, TIF-IA phosphomutant analysis\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — kinase-dead comparison with subcellular fractionation, single lab\",\n      \"pmids\": [\"26506235\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"ChIP-Seq after conditional inactivation of Rrn3 shows that preinitiation complex formation at rDNA is driven by UBF (UBTF) independently of transcription; loss of Rrn3 causes loss of Pol I from rDNA but an Enhancer Boundary Complex (CTCF/Cohesin) is stably maintained.\",\n      \"method\": \"High-resolution ChIP-Seq, conditional gene inactivation\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP-Seq with conditional KO; Rrn3 inactivation used as tool to define chromatin architecture\",\n      \"pmids\": [\"28715449\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"TIF-IA degradation by specific NF-κB stress stimuli is dependent on UBF/p14ARF and Ser44 of TIF-IA, and precedes NF-κB activation; blocking TIF-IA degradation blocks stress effects on nucleolar size and NF-κB signaling, defining a TIF-IA-NF-κB nucleolar stress response pathway. CDK4 inhibition mimics TIF-IA degradation.\",\n      \"method\": \"RNAi knockdown, TIF-IA mutant (S44) analysis, CDK4 inhibitor treatment, co-immunoprecipitation, NF-κB reporter assay, ex vivo tissue analysis\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — multiple mechanistic assays but pathway partially defined, single lab\",\n      \"pmids\": [\"29873780\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Under nutrient deprivation, phosphorylation of RRN3 at Ser199 causes its translocation from nucleolus to nuclear plasma, where it regulates alternative polyadenylation (APA) of autophagy-related mRNAs (e.g., OPTN), enhancing their stability and promoting autophagy.\",\n      \"method\": \"Long-read RNA sequencing, PAR-CLIP, cellular fractionation, phosphomutant analysis, in vivo tumor xenograft\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple methods including PAR-CLIP and phosphomutant analysis from single lab\",\n      \"pmids\": [\"41271632\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"In proliferating cells, TIF-IA binds to the cargo receptor p62 (SQSTM1); ATM activation during senescence disrupts this interaction, causing TIF-IA accumulation in the nucleus/nucleolus, which is essential for nucleolar phenotypic changes, SASP establishment, and increased ROS levels in senescence.\",\n      \"method\": \"Co-immunoprecipitation, ATM inhibition, multiple senescence models (OIS and TIS), mouse models, ROS measurement\",\n      \"journal\": \"Aging cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP with ATM-dependent mechanism validated in multiple models\",\n      \"pmids\": [\"41466483\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"EGR1 activates RRN3 gene transcription by binding to the RRN3 promoter, and also directly interacts with Pol I transcription machinery components via its DNA-binding domain to enhance their recruitment to the rDNA promoter.\",\n      \"method\": \"ChIP, promoter reporter assay, co-immunoprecipitation, RNAi knockdown, in vivo tumor model\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP and co-IP from single lab\",\n      \"pmids\": [\"41507426\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RRN3/TIF-IA is a conserved, growth-regulated RNA polymerase I initiation factor with a HEAT repeat fold that directly binds Pol I (via the A43/RPA43 subunit interface) and the core promoter factor (SL1/CF), bridging Pol I to the rDNA promoter; its activity is controlled by a phosphorylation code involving multiple kinases (ERK/RSK at S633/S649, mTOR-dependent S44, JNK2 at T200, CK2 at S170/172) and a phosphatase (FCP1), which regulate its association with Pol I, its nucleolar localization, and its release after initiation; it also has intrinsic DNA-binding activity essential for transcription, functions stoichiometrically (becoming inactivated after each round), and under stress conditions can redistribute to the nucleoplasm to regulate alternative polyadenylation of autophagy mRNAs.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"RRN3 (TIF-IA) is a conserved, growth-regulated RNA polymerase I transcription initiation factor that bridges Pol I to the rDNA promoter and couples nutrient/growth factor signaling to ribosome biogenesis. It adopts a HEAT repeat fold and directly engages the Pol I subunit RPA43 (via a phosphorylation-dependent interface) and the promoter selectivity factor SL1/TIF-IB (via a LARAK motif), converting inactive Pol I dimers into initiation-competent monomers; it also possesses intrinsic DNA-binding activity essential for transcription and functions stoichiometrically, becoming inactivated after each initiation round through CK2-mediated phosphorylation at Ser170/172, with FCP1 phosphatase recycling it for subsequent rounds [PMID:8413268, PMID:20, PMID:18559419, PMID:23393135]. A multisite phosphorylation code integrates signals from ERK/RSK (Ser633/649), mTOR (Ser44/Ser199), JNK2 (Thr200), CK2, and Akt to control RRN3 activity, Pol I association, and nucleolar versus nucleoplasmic localization; genetic inactivation of RRN3 triggers nucleolar disruption, ribosomal protein L11-MDM2-dependent p53 stabilization, and apoptosis [PMID:12620228, PMID:15004009, PMID:15805466, PMID:15989966]. Beyond canonical Pol I transcription, nutrient deprivation-induced Ser199 phosphorylation relocates RRN3 to the nucleoplasm where it regulates alternative polyadenylation of autophagy mRNAs, and during senescence ATM-dependent disruption of its interaction with SQSTM1/p62 drives nucleolar remodeling and SASP establishment [PMID:41271632, PMID:41466483].\",\n  \"teleology\": [\n    {\n      \"year\": 1985,\n      \"claim\": \"Identification of TIF-IA as a growth-dependent factor required for Pol I transcription initiation established that rRNA synthesis is regulated at the level of a dissociable initiation factor whose activity is lost in quiescent cells.\",\n      \"evidence\": \"Biochemical fractionation and in vitro transcription reconstitution from mouse cell extracts\",\n      \"pmids\": [\"4070001\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular identity of TIF-IA unknown\", \"No phosphorylation data\", \"Mechanism of growth regulation unresolved\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Demonstration that TIF-IA is a 75 kDa monomer that associates with Pol I, is required for the first phosphodiester bond but not preinitiation complex assembly, and is released after initiation revealed its stoichiometric, single-use nature in transcription.\",\n      \"evidence\": \"Purified reconstituted transcription system with template commitment assays\",\n      \"pmids\": [\"8413268\", \"2390974\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Gene identity not yet cloned\", \"Mechanism of post-initiation release unknown\", \"No structural information\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Cloning of yeast RRN3 and demonstration that Rrn3p directly binds Pol I independently of DNA and stimulates promoter recruitment established RRN3 as the yeast counterpart of TIF-IA and a universal Pol I initiation factor.\",\n      \"evidence\": \"Immunoaffinity purification, in vitro transcription complementation, and Sarkosyl-resistant complex assays in yeast\",\n      \"pmids\": [\"8670901\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mammalian gene not yet cloned\", \"Binding interface on Pol I unresolved\", \"Phospho-regulatory mechanism unknown\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Identification of the RPA43 subunit as the direct Rrn3 binding partner on Pol I, and Rrn6 (core factor) as the promoter-side contact, established the bridging model whereby Rrn3 physically connects Pol I to the promoter-bound core factor; concurrent cloning of mammalian TIF-IA as the RRN3 homolog confirmed functional conservation across eukaryotes.\",\n      \"evidence\": \"Genetic suppression, synthetic lethality, co-expression in E. coli, two-hybrid, yeast complementation with human RRN3\",\n      \"pmids\": [\"11032814\", \"11265758\", \"10758157\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Detailed binding interface unresolved at atomic level\", \"Phosphorylation sites not yet mapped in mammals\", \"Mechanism of growth-dependent regulation still unclear\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Mapping of TIF-IA interaction domains (aa 512–609 for Pol I, LARAK motif for SL1) and demonstration that phosphorylation state controls the Rrn3–Pol I interaction resolved how growth signals converge on TIF-IA at the molecular level.\",\n      \"evidence\": \"Deletion mutant mapping, co-immunoprecipitation, phosphatase treatment, comparison of phosphorylated vs. unphosphorylated recombinant Rrn3\",\n      \"pmids\": [\"12393749\", \"12015311\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific kinases not yet identified\", \"Stoichiometric versus catalytic action still debated\", \"Structural basis of phospho-regulation unknown\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Identification of ERK/RSK phosphorylation at Ser633/649 as activating modifications directly linked MAPK growth factor signaling to Pol I transcription via TIF-IA, while demonstration that Rrn3 functions stoichiometrically (becoming inactivated after each round) explained why its continual reactivation is required.\",\n      \"evidence\": \"Phosphopeptide mapping, site-directed mutagenesis, kinase inhibitor treatment, in vivo rRNA synthesis assays, post-transcription reuse assays\",\n      \"pmids\": [\"12620228\", \"12646563\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Other regulatory kinases not yet identified\", \"Mechanism of inactivation after initiation unclear\", \"No structural data\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Discovery that mTOR regulates TIF-IA via opposing phosphorylations at Ser44 (activating) and Ser199 (inactivating) established a second major signaling axis controlling Pol I transcription and showed that mTOR inhibition causes cytoplasmic translocation of TIF-IA.\",\n      \"evidence\": \"Rapamycin treatment, phosphomutant analysis, subcellular fractionation in mammalian cells\",\n      \"pmids\": [\"15004009\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct mTOR kinase activity on TIF-IA not demonstrated\", \"Relationship between mTOR and ERK/RSK inputs unclear\", \"In vivo physiological relevance in whole organism not tested\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Identification of JNK2-mediated Thr200 phosphorylation as a stress-responsive inactivating modification that disrupts both Pol I and SL1 interactions, and genetic demonstration that TIF-IA loss activates p53 via the RPL11-MDM2 pathway, placed TIF-IA at the nexus of nucleolar stress sensing.\",\n      \"evidence\": \"JNK2 kinase assays, site-directed mutagenesis, Jnk2-KO cells, TIF-IA conditional knockout in MEFs, co-IP of L11-MDM2\",\n      \"pmids\": [\"15805466\", \"15989966\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether JNK2 directly phosphorylates TIF-IA in vivo or acts through intermediary unclear\", \"Full spectrum of stress signals converging on TIF-IA not mapped\", \"Drosophila TOR-TIF-IA axis not yet confirmed\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Conservation of TOR-dependent TIF-IA regulation in Drosophila and discovery that Pol I subunits Rpa34/Rpa49 regulate both Rrn3 recruitment and its post-initiation release broadened the mechanistic picture to include polymerase-intrinsic control of the Rrn3 cycle.\",\n      \"evidence\": \"Drosophila TIF-IA mutants with ChIP and TOR epistasis; yeast rpa49 mutant ChIP and polymerase occupancy assays\",\n      \"pmids\": [\"18086911\", \"18086878\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of Rpa49-mediated Rrn3 release unknown\", \"Whether mammalian PAF53/CAST ortholog has equivalent role not tested\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identification of CK2-mediated Ser170/172 phosphorylation as the trigger for TIF-IA release from RPA43 after initiation, and FCP1 phosphatase as the recycling enzyme, completed the phosphorylation cycle model explaining how TIF-IA is used stoichiometrically yet continuously recycled.\",\n      \"evidence\": \"In vitro kinase assay, site-directed mutagenesis, FRAP, ChIP, covalent tethering of TIF-IA to RPA43\",\n      \"pmids\": [\"18559419\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CK2 acts co-transcriptionally or post-initiation not resolved\", \"Interplay between CK2 Ser170/172 and other phospho-sites unclear\", \"Structural view of phospho-dependent release absent\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"The crystal structure of Rrn3 revealed a HEAT repeat fold with a surface serine patch whose phosphorylation blocks Pol I binding, providing the first atomic-level explanation for how phosphorylation acts as an on/off switch for Pol I initiation.\",\n      \"evidence\": \"X-ray crystallography, cross-linking mass spectrometry, phosphomimetic mutagenesis, ChIP, cell growth assays\",\n      \"pmids\": [\"21940764\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structure of the Pol I–Rrn3 complex at this point\", \"How the serine patch integrates signals from multiple kinases structurally unresolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Discovery that Rrn3 possesses intrinsic DNA-binding activity via an HSF2-like domain (aa 382–400) essential for transcription but dispensable for Pol I/SL1 binding revealed a previously unsuspected direct contact with the rDNA template.\",\n      \"evidence\": \"DNA-binding assays, domain mutagenesis, in vitro transcription, yeast complementation\",\n      \"pmids\": [\"23393135\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Target DNA sequence specificity not defined\", \"How DNA binding cooperates with Pol I/SL1 contacts structurally unknown\", \"Whether DNA binding is regulated by phosphorylation untested\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"The cryo-EM structure of the Pol I–Rrn3 complex at 4.8 Å revealed that Rrn3 binding converts the inactive Pol I dimer into a monomeric initiation-competent form, providing the structural basis for the activation mechanism.\",\n      \"evidence\": \"Cryo-electron microscopy structural determination\",\n      \"pmids\": [\"27418309\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Resolution insufficient for side-chain detail at interface\", \"Ternary complex with promoter factors and DNA not captured\", \"Mechanism of dimer disruption not fully resolved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Discovery that Ser199-phosphorylated RRN3 translocates to the nucleoplasm under nutrient deprivation and regulates alternative polyadenylation of autophagy mRNAs (e.g., OPTN) established a non-canonical, Pol I-independent function in mRNA metabolism and autophagy.\",\n      \"evidence\": \"Long-read RNA sequencing, PAR-CLIP, cellular fractionation, phosphomutant analysis, in vivo tumor xenograft\",\n      \"pmids\": [\"41271632\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of APA regulation (direct RNA binding vs. cofactor recruitment) not fully defined\", \"Not independently replicated\", \"Scope of target mRNAs beyond autophagy genes unclear\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Identification of ATM-dependent disruption of the TIF-IA–SQSTM1/p62 interaction during senescence, leading to nuclear TIF-IA accumulation essential for SASP and nucleolar remodeling, extended TIF-IA function to senescence biology beyond its canonical Pol I role.\",\n      \"evidence\": \"Co-immunoprecipitation, ATM inhibition, oncogene- and therapy-induced senescence models, mouse models\",\n      \"pmids\": [\"41466483\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"ATM phosphorylation site on TIF-IA or p62 not mapped\", \"Whether nuclear TIF-IA drives senescence phenotypes through Pol I activity or other mechanisms unclear\", \"Not independently replicated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include how RRN3's DNA-binding, Pol I-bridging, and newly discovered mRNA-regulatory functions are coordinated; how the multisite phosphorylation code is integrated at the structural level; and whether non-canonical nucleoplasmic functions of RRN3 operate independently of its role in Pol I transcription.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution ternary complex structure with promoter DNA and SL1\", \"Phosphorylation code integration across kinases not modeled structurally\", \"Non-canonical mRNA regulatory mechanism needs independent replication and full target identification\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [21]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 2, 3, 6]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1, 5, 17, 24]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [19, 22, 30]},\n      {\"term_id\": \"GO:0005654\", \"supporting_discovery_ids\": [14, 19, 29]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [12, 19]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 2, 3, 5, 6, 11, 17, 24]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [11, 12, 14, 22]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [29]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [13, 14, 25, 28]}\n    ],\n    \"complexes\": [\n      \"Pol I–Rrn3 initiation complex\"\n    ],\n    \"partners\": [\n      \"RPA43\",\n      \"POLR1A\",\n      \"TAF1A\",\n      \"TAF1B\",\n      \"SQSTM1\",\n      \"CTDP1\",\n      \"CSNK2A1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}