{"gene":"TXNL4A","run_date":"2026-06-10T10:51:56","timeline":{"discoveries":[{"year":1999,"finding":"Fission yeast dim1p is required for entry into mitosis and chromosome segregation; deletion causes lethal G2 arrest, and this lethality is rescued by overexpression of the mouse dim1 homolog (mdim1), demonstrating functional conservation. dim1-35 temperature-sensitive cells arrest with low histone H1 kinase activity and show sensitivity to the microtubule-destabilizing drug thiabendazole.","method":"Genetic deletion, temperature-sensitive mutant analysis, heterologous complementation, histone H1 kinase assay, drug sensitivity assay","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with defined cellular phenotype (G2 arrest, failed chromosome segregation), heterologous complementation across species, replicated in multiple genetic backgrounds","pmids":["9182666"],"is_preprint":false},{"year":1999,"finding":"S. pombe dim1p maintains the steady-state level of the APC/C component lid1p. In dim1 mutants, lid1p abundance and the 20S APC/C complex decline significantly, and ubiquitination of the APC/C target cut2p is abolished. Genetic synthetic-lethal interaction places dim1 upstream of APC/C function.","method":"Synthetic lethal screen, co-immunoprecipitation, sucrose gradient sedimentation, ubiquitination assay, epitope tagging","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, biochemical complex analysis, functional ubiquitination assay, genetic epistasis, multiple orthogonal methods in one study","pmids":["10082519"],"is_preprint":false},{"year":1999,"finding":"Human Dim1 (hDim1/U5-15kD/TXNL4A) adopts a thioredoxin fold structure as determined by NMR and molecular modeling. The ~125 of 142 amino acids define a novel sixth branch of the thioredoxin superfamily. Removal of the C-terminal extension (residues 129–142) generates a dominant-negative form that induces G2 cell cycle arrest when overproduced, via altered interactions with partner molecules.","method":"NMR structural analysis, molecular modeling, alanine scanning mutagenesis, cell cycle analysis by overexpression","journal":"Physiological genomics","confidence":"High","confidence_rationale":"Tier 1 / Moderate — NMR structure combined with mutagenesis and functional cell-cycle assay in a single study, single lab but multiple orthogonal methods","pmids":["11015569"],"is_preprint":false},{"year":2000,"finding":"Human U5-15kD (TXNL4A) interacts with PQBP-1 (polyglutamine tract-binding protein-1) through PQBP-1's C-terminal domain (CTD), placing TXNL4A in a complex with a protein implicated in splicing and the polyglutamine disease pathway.","method":"Two-hybrid screen, co-immunoprecipitation, domain-deletion mapping","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single Co-IP with domain mapping, replicated in a subsequent independent study (PMID:20307692)","pmids":["10873650"],"is_preprint":false},{"year":2000,"finding":"Dim1 (hDim1/TXNL4A) interacts with pre-mRNA splicing factors hnRNP F and Npw38/PQBP-1. Two-hybrid reiterative screening identified exclusively splicing-related partners. Saturating alanine scanning mutagenesis of Dim1 mapped residues essential for these interactions to a defined surface sector on the thioredoxin fold. Co-expression of one partner induced synthetic growth arrest in mammalian cells.","method":"Yeast two-hybrid screening, alanine scanning mutagenesis, structural mapping, mammalian co-expression phenotypic assay, C. elegans RNAi (embryonic lethality upon DML-1 depletion)","journal":"Gene","confidence":"High","confidence_rationale":"Tier 2 / Moderate — two-hybrid with mutagenesis, structural mapping of interaction interface, in vivo functional validation by RNAi, multiple orthogonal approaches in one study","pmids":["11054566"],"is_preprint":false},{"year":1999,"finding":"Human U5-15kD (TXNL4A) was overexpressed in E. coli, purified, and crystallized in space group P21212, diffracting to at least 3.0 Å, establishing the protein is amenable to crystallographic structure determination.","method":"Recombinant protein expression, purification, X-ray crystallography (preliminary diffraction)","journal":"Acta crystallographica. Section D, Biological crystallography","confidence":"Low","confidence_rationale":"Tier 1 / Weak — preliminary crystallography only, no structure solved yet, single study","pmids":["10089325"],"is_preprint":false},{"year":2010,"finding":"PQBP-1 binds to U5-15kD (TXNL4A) via a continuous 23-residue segment within PQBP-1's C-terminal domain. Frameshift mutations in PQBP-1 associated with X-linked mental retardation truncate this segment and abolish binding to U5-15kD.","method":"Recombinant protein binding assays, NMR, deletion/mutation mapping","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro binding assay with precise residue mapping and NMR confirmation, single lab","pmids":["20307692"],"is_preprint":false},{"year":2014,"finding":"Biallelic mutations in TXNL4A cause Burn-McKeown syndrome (BMKS). Promoter deletions reduce TXNL4A expression (shown by reporter gene and in vivo assays). Depletion of TXNL4A (Dib1) in yeast reduces assembly of the U4/U6·U5 tri-snRNP complex.","method":"Patient genetics, reporter gene assays, in vivo expression assays, yeast Dib1 depletion with tri-snRNP assembly analysis","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — functional promoter assays, direct tri-snRNP assembly readout upon depletion, genetic and biochemical evidence from multiple families and model organism","pmids":["25434003"],"is_preprint":false},{"year":2014,"finding":"Dim1 (TXNL4A) negatively regulates osteoclastogenesis by directly associating with c-Fos and preventing c-Fos from binding to the NFATc1 promoter, thereby repressing NFATc1 transcription. RNAi knockdown of Dim1 enhanced NFATc1 expression and osteoclast differentiation; ectopic Dim1 overexpression suppressed it.","method":"RNAi knockdown, ectopic overexpression, ChIP assay, co-immunoprecipitation, osteoclast differentiation assay (TRAP staining, bone resorption)","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP and Co-IP establish direct protein-DNA and protein-protein interactions, KD/OE with defined functional readout, single lab","pmids":["25023277"],"is_preprint":false},{"year":2016,"finding":"Binding of PQBP-1 to WBP11 (via PQBP-1's WW domain) allosterically reduces the binding affinity of PQBP-1 for U5-15kD (TXNL4A), demonstrating that PQBP-1's interactions with two spliceosomal partners are allosterically coupled.","method":"In vitro binding assays, NMR titration, isothermal titration calorimetry","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — quantitative in vitro binding with NMR and ITC, single lab, direct demonstration of allosteric modulation","pmids":["27314904"],"is_preprint":false},{"year":2018,"finding":"Yeast Dib1 (TXNL4A ortholog) functions to prevent premature spliceosome activation at the B-to-Bact transition. Temperature-sensitive dib1 mutants stall in vitro splicing prior to the first catalytic step and block assembly at the B complex. Dib1 exchanges readily in splicing extracts despite being a U5 snRNP component, indicating dynamic rather than static association.","method":"In vitro splicing assay with temperature-sensitive mutants, spliceosome assembly assay, protein exchange experiments in splicing extracts, circular dichroism","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — in vitro reconstitution splicing assay with defined mutants, assembly checkpoint identified, multiple biochemical approaches, single lab","pmids":["29715471"],"is_preprint":false},{"year":2020,"finding":"TXNL4A lacks a classical nuclear localization signal and relies on PQBP-1 for nuclear import via a piggyback mechanism through the karyopherin β2 receptor. The PQBP-1 P244L missense mutation (X-linked intellectual disability) disrupts the PQBP-1–TXNL4A interaction and mislocalizes TXNL4A.","method":"Recombinant protein expression, in vitro binding assays, immunofluorescence microscopy in HeLa cells, PQBP-1 mutant analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — in vitro binding combined with direct subcellular localization imaging, disease mutation validation, multiple PQBP-1 variants tested, single lab with orthogonal methods","pmids":["32041777"],"is_preprint":false},{"year":2022,"finding":"Knockdown of Txnl4a in Xenopus embryos causes defects in cranial neural crest cell formation, establishing a direct role for TXNL4A in neural crest development underlying mandibulofacial dysostosis (Burn-McKeown syndrome). This parallels phenotypes from EFTUD2 and SNRPB knockdowns, pointing to a common spliceosomopathy mechanism.","method":"Morpholino-mediated knockdown in Xenopus embryos, neural crest marker analysis, craniofacial cartilage staining","journal":"Journal of developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct loss-of-function in vivo with defined developmental phenotype (neural crest depletion), single lab, single model organism","pmids":["35893124"],"is_preprint":false},{"year":2006,"finding":"Human Dim1 (TXNL4A) has peptidase activity with autocleavage, generating a thioredoxin-like core fragment. This truncated form retains peptidase activity. The autocleavage product corresponds to the dominant-negative fragment previously shown to cause G2 arrest.","method":"In vitro biochemical peptidase assay, autocleavage detection by SDS-PAGE/mass spectrometry","journal":"Chemical biology & drug design","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single biochemical assay, single lab, no mutagenesis to identify active-site residues, substrate not identified","pmids":["17177886"],"is_preprint":false},{"year":2017,"finding":"The ATPase Fap7 promotes formation of the rotated state of pre-40S ribosomes and releases Dim1 (TXNL4A ortholog) from nascent 40S subunits during ribosome maturation. This quality-control step links ribosome assembly to translocation competence; bypassing it causes reading-frame maintenance defects.","method":"Genetic epistasis, biochemical ribosome assembly assays, ATPase activity measurements, in vivo translation fidelity assay","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic and biochemical experiments, functional translation assay, mechanistic model validated by multiple orthogonal approaches, published in high-impact journal","pmids":["28890337"],"is_preprint":false}],"current_model":"TXNL4A (U5-15kD/Dib1/Dim1) is an essential, evolutionarily conserved thioredoxin-fold protein that functions as a core component of the U5 snRNP and U4/U6·U5 tri-snRNP: it prevents premature spliceosome activation at the B-to-Bact transition by occupying a position adjacent to U6 snRNA and U5 loop I, is released during the B-to-Bact step, and is required for tri-snRNP assembly; its nuclear import depends on a piggyback mechanism via PQBP-1 and karyopherin β2; PQBP-1 binding to WBP11 allosterically modulates PQBP-1's affinity for TXNL4A; in parallel, TXNL4A binds c-Fos to repress NFATc1 transcription and osteoclastogenesis; in ribosome biogenesis, the Dim1 ortholog is released from pre-40S by the ATPase Fap7 as part of a quality-control translocation-like cycle; and biallelic loss-of-function mutations in TXNL4A—commonly a promoter deletion combined with a coding variant—cause Burn-McKeown syndrome by reducing TXNL4A expression and impairing splicing, with cranial neural crest cell formation as the critical developmental target."},"narrative":{"mechanistic_narrative":"TXNL4A (Dim1/Dib1/U5-15kD) is an essential, evolutionarily conserved thioredoxin-fold protein that functions as a core regulator of pre-mRNA splicing within the U5 snRNP and U4/U6·U5 tri-snRNP, where it acts as a checkpoint preventing premature spliceosome activation [PMID:25434003, PMID:29715471]. As a temperature-sensitive Dib1 mutant stalls in vitro splicing before the first catalytic step and blocks assembly at the B complex, while exchanging dynamically in splicing extracts, TXNL4A gates the B-to-Bact transition rather than serving as a static structural subunit [PMID:29715471]; its depletion reduces U4/U6·U5 tri-snRNP assembly [PMID:25434003]. Structurally, the protein adopts a thioredoxin fold defining a distinct branch of that superfamily, and removal of its C-terminal extension yields a dominant-negative form that arrests cells in G2 [PMID:11015569]. TXNL4A engages the spliceosome-associated factor PQBP-1 through a defined 23-residue segment of PQBP-1's C-terminal domain [PMID:10873650, PMID:20307692], and because TXNL4A lacks a classical nuclear localization signal, it is imported into the nucleus by a piggyback mechanism on PQBP-1 via karyopherin β2; disease mutations in PQBP-1 disrupt this interaction and mislocalize TXNL4A [PMID:32041777]. PQBP-1's affinity for TXNL4A is allosterically reduced when PQBP-1 binds WBP11 through its WW domain, coupling TXNL4A's handling to other spliceosomal interactions [PMID:27314904]. Biallelic loss-of-function mutations in TXNL4A—typically a promoter deletion reducing expression combined with a coding variant—cause Burn-McKeown syndrome by impairing splicing, with cranial neural crest cell formation as the critical developmental target [PMID:25434003, PMID:35893124]. Beyond splicing, TXNL4A directly associates with c-Fos to block its binding to the NFATc1 promoter, repressing NFATc1 transcription and osteoclastogenesis [PMID:25023277], and across species its orthologs are required for mitotic entry, chromosome segregation, and APC/C function [PMID:9182666, PMID:10082519].","teleology":[{"year":1999,"claim":"Established that the Dim1 protein is essential and functionally conserved for cell cycle progression, answering whether a thioredoxin-like protein has a defined in vivo cellular requirement.","evidence":"Fission yeast genetic deletion and temperature-sensitive mutants with heterologous mouse complementation and histone H1 kinase assays","pmids":["9182666"],"confidence":"High","gaps":["Did not define the molecular activity producing G2 arrest","Link to splicing not yet identified"]},{"year":1999,"claim":"Connected dim1 function to APC/C-mediated ubiquitination, framing a possible mechanism for its mitotic phenotype.","evidence":"Synthetic-lethal screen, reciprocal Co-IP, sucrose gradient sedimentation and ubiquitination assays in S. pombe","pmids":["10082519"],"confidence":"High","gaps":["Whether the APC/C link is direct or downstream of a splicing defect was not resolved","No biochemical demonstration that Dim1 acts on APC/C components enzymatically"]},{"year":1999,"claim":"Showed the protein is amenable to crystallographic study, a prerequisite for structural mechanism.","evidence":"Recombinant expression, purification and preliminary X-ray diffraction","pmids":["10089325"],"confidence":"Low","gaps":["Preliminary crystallography only — no structure solved","No functional inference possible"]},{"year":2000,"claim":"Defined the thioredoxin fold and showed that a C-terminally truncated form is dominant-negative, linking structure to the cell cycle phenotype.","evidence":"NMR structural analysis, molecular modeling, alanine scanning, and overexpression cell-cycle assays","pmids":["11015569"],"confidence":"High","gaps":["Redox or catalytic role of the thioredoxin fold not demonstrated","Mechanism by which the dominant-negative fragment arrests cells unresolved"]},{"year":2000,"claim":"Reoriented the protein toward splicing by identifying exclusively splicing-related interaction partners, including PQBP-1 and hnRNP F.","evidence":"Yeast two-hybrid and reiterative screening, alanine scanning with structural interface mapping, mammalian co-expression and C. elegans RNAi","pmids":["10873650","11054566"],"confidence":"High","gaps":["Did not establish where in the splicing cycle TXNL4A acts","Functional consequence of each interaction not dissected"]},{"year":2010,"claim":"Mapped the precise PQBP-1 segment binding TXNL4A and linked its disruption to X-linked mental retardation, giving the interaction disease relevance.","evidence":"Recombinant binding assays, NMR, and deletion/mutation mapping of PQBP-1 frameshift variants","pmids":["20307692"],"confidence":"Medium","gaps":["Functional readout of binding loss in cells not measured here","Did not address nuclear import role"]},{"year":2014,"claim":"Identified TXNL4A loss-of-function as the cause of Burn-McKeown syndrome and tied reduced expression to impaired tri-snRNP assembly, unifying genetics with splicing mechanism.","evidence":"Patient genetics, promoter reporter and in vivo expression assays, and yeast Dib1 depletion with tri-snRNP assembly analysis","pmids":["25434003"],"confidence":"High","gaps":["Tissue specificity of the splicing defect not explained","Which transcripts are misspliced in patients not defined"]},{"year":2014,"claim":"Revealed a splicing-independent transcriptional role in which TXNL4A represses NFATc1 and osteoclastogenesis by sequestering c-Fos.","evidence":"RNAi knockdown, overexpression, ChIP, Co-IP, and osteoclast differentiation assays","pmids":["25023277"],"confidence":"Medium","gaps":["Single lab; reciprocal validation of the c-Fos interaction limited","Relationship between nuclear splicing pool and c-Fos-bound pool unclear"]},{"year":2016,"claim":"Demonstrated that PQBP-1's two spliceosomal interactions are allosterically coupled, refining how TXNL4A handling is regulated.","evidence":"In vitro binding assays, NMR titration, and isothermal titration calorimetry","pmids":["27314904"],"confidence":"Medium","gaps":["Physiological consequence of the allosteric coupling in cells not shown","Single lab in vitro system"]},{"year":2017,"claim":"Uncovered a role for the Dim1 ortholog in ribosome biogenesis, showing its release from pre-40S by the ATPase Fap7 is a translation-fidelity quality-control step.","evidence":"Genetic epistasis, biochemical ribosome assembly assays, ATPase measurements, and in vivo translation fidelity assays in yeast","pmids":["28890337"],"confidence":"High","gaps":["Whether human TXNL4A participates in ribosome biogenesis not tested","Note: this ortholog activity may reflect a paralog (Dim1/DIMT1) rather than TXNL4A itself"]},{"year":2018,"claim":"Defined the precise step of action: Dib1 prevents premature spliceosome activation at the B-to-Bact transition and associates dynamically rather than statically.","evidence":"In vitro splicing with temperature-sensitive mutants, assembly assays, protein exchange experiments, and circular dichroism","pmids":["29715471"],"confidence":"High","gaps":["Molecular trigger for Dib1 release not identified","Whether the thioredoxin fold has catalytic involvement in the checkpoint unresolved"]},{"year":2020,"claim":"Explained how TXNL4A reaches the nucleus, showing a piggyback import mechanism on PQBP-1 via karyopherin β2 disrupted by disease mutations.","evidence":"Recombinant binding assays, immunofluorescence in HeLa cells, and analysis of PQBP-1 P244L and other variants","pmids":["32041777"],"confidence":"High","gaps":["Whether alternative import routes exist not addressed","Quantitative contribution of import defect to disease phenotypes not measured"]},{"year":2022,"claim":"Connected TXNL4A loss to the developmental target of Burn-McKeown syndrome by demonstrating a requirement in cranial neural crest formation.","evidence":"Morpholino knockdown in Xenopus embryos with neural crest marker and craniofacial cartilage analysis","pmids":["35893124"],"confidence":"Medium","gaps":["Specific misspliced transcripts driving the neural crest defect not identified","Single model organism"]},{"year":null,"claim":"It remains unknown whether the thioredoxin fold of TXNL4A carries an enzymatic activity relevant to its splicing checkpoint role, and what molecular signal triggers its release at the B-to-Bact transition.","evidence":"","pmids":[],"confidence":"Low","gaps":["No active-site mutagenesis tying putative catalytic residues to splicing","Reported peptidase/autocleavage activity remains a single unconfirmed observation","Trigger for Dib1 release during activation undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[8]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[11]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[7,10]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[12]}],"complexes":["U5 snRNP","U4/U6·U5 tri-snRNP"],"partners":["PQBP-1","WBP11","HNRNP F","C-FOS"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P83876","full_name":"Thioredoxin-like protein 4A","aliases":["DIM1 protein homolog","Spliceosomal U5 snRNP-specific 15 kDa protein","Thioredoxin-like U5 snRNP protein U5-15kD"],"length_aa":142,"mass_kda":16.8,"function":"Plays a role in pre-mRNA splicing as component of the U5 snRNP and U4/U6-U5 tri-snRNP complexes that are involved in spliceosome assembly, and as component of the precatalytic spliceosome (spliceosome B complex)","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/P83876/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/TXNL4A","classification":"Common Essential","n_dependent_lines":1207,"n_total_lines":1208,"dependency_fraction":0.9991721854304636},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"EFTUD2","stoichiometry":4.0},{"gene":"PRPF4B","stoichiometry":4.0},{"gene":"PRPF8","stoichiometry":4.0},{"gene":"SNRNP40","stoichiometry":4.0},{"gene":"CD2BP2","stoichiometry":0.2},{"gene":"CHMP2A","stoichiometry":0.2},{"gene":"CPSF6","stoichiometry":0.2},{"gene":"RBM39","stoichiometry":0.2},{"gene":"RBM42","stoichiometry":0.2},{"gene":"SF3A1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/TXNL4A","total_profiled":1310},"omim":[{"mim_id":"618083","title":"WW-BINDING PROTEIN 11; WBP11","url":"https://www.omim.org/entry/618083"},{"mim_id":"617722","title":"THIOREDOXIN-LIKE 4B; TXNL4B","url":"https://www.omim.org/entry/617722"},{"mim_id":"616462","title":"ACROFACIAL DYSOSTOSIS, CINCINNATI TYPE; AFDCIN","url":"https://www.omim.org/entry/616462"},{"mim_id":"611595","title":"THIOREDOXIN-LIKE 4A; TXNL4A","url":"https://www.omim.org/entry/611595"},{"mim_id":"608572","title":"BURN-MCKEOWN SYNDROME; BMKS","url":"https://www.omim.org/entry/608572"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/TXNL4A"},"hgnc":{"alias_symbol":["U5-15kD","DIM1","HsT161","DIB1","SNRNP15"],"prev_symbol":["TXNL4"]},"alphafold":{"accession":"P83876","domains":[{"cath_id":"3.40.30.10","chopping":"10-130","consensus_level":"high","plddt":92.8921,"start":10,"end":130}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P83876","model_url":"https://alphafold.ebi.ac.uk/files/AF-P83876-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P83876-F1-predicted_aligned_error_v6.png","plddt_mean":88.56},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TXNL4A","jax_strain_url":"https://www.jax.org/strain/search?query=TXNL4A"},"sequence":{"accession":"P83876","fasta_url":"https://rest.uniprot.org/uniprotkb/P83876.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P83876/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P83876"}},"corpus_meta":[{"pmid":"8064863","id":"PMC_8064863","title":"The DIM1 gene responsible for the conserved m6(2)Am6(2)A dimethylation in the 3'-terminal loop of 18 S rRNA is essential in yeast.","date":"1994","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/8064863","citation_count":144,"is_preprint":false},{"pmid":"10873650","id":"PMC_10873650","title":"PQBP-1/Npw38, a nuclear protein binding to the polyglutamine tract, interacts with U5-15kD/dim1p via the carboxyl-terminal domain.","date":"2000","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/10873650","citation_count":75,"is_preprint":false},{"pmid":"11054566","id":"PMC_11054566","title":"Evidence that dim1 associates with proteins involved in pre-mRNA splicing, and delineation of residues essential for dim1 interactions with hnRNP F and 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In dim1 mutants, lid1p abundance and the 20S APC/C complex decline significantly, and ubiquitination of the APC/C target cut2p is abolished. Genetic synthetic-lethal interaction places dim1 upstream of APC/C function.\",\n      \"method\": \"Synthetic lethal screen, co-immunoprecipitation, sucrose gradient sedimentation, ubiquitination assay, epitope tagging\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, biochemical complex analysis, functional ubiquitination assay, genetic epistasis, multiple orthogonal methods in one study\",\n      \"pmids\": [\"10082519\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Human Dim1 (hDim1/U5-15kD/TXNL4A) adopts a thioredoxin fold structure as determined by NMR and molecular modeling. The ~125 of 142 amino acids define a novel sixth branch of the thioredoxin superfamily. Removal of the C-terminal extension (residues 129–142) generates a dominant-negative form that induces G2 cell cycle arrest when overproduced, via altered interactions with partner molecules.\",\n      \"method\": \"NMR structural analysis, molecular modeling, alanine scanning mutagenesis, cell cycle analysis by overexpression\",\n      \"journal\": \"Physiological genomics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — NMR structure combined with mutagenesis and functional cell-cycle assay in a single study, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"11015569\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Human U5-15kD (TXNL4A) interacts with PQBP-1 (polyglutamine tract-binding protein-1) through PQBP-1's C-terminal domain (CTD), placing TXNL4A in a complex with a protein implicated in splicing and the polyglutamine disease pathway.\",\n      \"method\": \"Two-hybrid screen, co-immunoprecipitation, domain-deletion mapping\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single Co-IP with domain mapping, replicated in a subsequent independent study (PMID:20307692)\",\n      \"pmids\": [\"10873650\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Dim1 (hDim1/TXNL4A) interacts with pre-mRNA splicing factors hnRNP F and Npw38/PQBP-1. Two-hybrid reiterative screening identified exclusively splicing-related partners. Saturating alanine scanning mutagenesis of Dim1 mapped residues essential for these interactions to a defined surface sector on the thioredoxin fold. Co-expression of one partner induced synthetic growth arrest in mammalian cells.\",\n      \"method\": \"Yeast two-hybrid screening, alanine scanning mutagenesis, structural mapping, mammalian co-expression phenotypic assay, C. elegans RNAi (embryonic lethality upon DML-1 depletion)\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two-hybrid with mutagenesis, structural mapping of interaction interface, in vivo functional validation by RNAi, multiple orthogonal approaches in one study\",\n      \"pmids\": [\"11054566\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Human U5-15kD (TXNL4A) was overexpressed in E. coli, purified, and crystallized in space group P21212, diffracting to at least 3.0 Å, establishing the protein is amenable to crystallographic structure determination.\",\n      \"method\": \"Recombinant protein expression, purification, X-ray crystallography (preliminary diffraction)\",\n      \"journal\": \"Acta crystallographica. Section D, Biological crystallography\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 1 / Weak — preliminary crystallography only, no structure solved yet, single study\",\n      \"pmids\": [\"10089325\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PQBP-1 binds to U5-15kD (TXNL4A) via a continuous 23-residue segment within PQBP-1's C-terminal domain. Frameshift mutations in PQBP-1 associated with X-linked mental retardation truncate this segment and abolish binding to U5-15kD.\",\n      \"method\": \"Recombinant protein binding assays, NMR, deletion/mutation mapping\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro binding assay with precise residue mapping and NMR confirmation, single lab\",\n      \"pmids\": [\"20307692\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Biallelic mutations in TXNL4A cause Burn-McKeown syndrome (BMKS). Promoter deletions reduce TXNL4A expression (shown by reporter gene and in vivo assays). Depletion of TXNL4A (Dib1) in yeast reduces assembly of the U4/U6·U5 tri-snRNP complex.\",\n      \"method\": \"Patient genetics, reporter gene assays, in vivo expression assays, yeast Dib1 depletion with tri-snRNP assembly analysis\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — functional promoter assays, direct tri-snRNP assembly readout upon depletion, genetic and biochemical evidence from multiple families and model organism\",\n      \"pmids\": [\"25434003\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Dim1 (TXNL4A) negatively regulates osteoclastogenesis by directly associating with c-Fos and preventing c-Fos from binding to the NFATc1 promoter, thereby repressing NFATc1 transcription. RNAi knockdown of Dim1 enhanced NFATc1 expression and osteoclast differentiation; ectopic Dim1 overexpression suppressed it.\",\n      \"method\": \"RNAi knockdown, ectopic overexpression, ChIP assay, co-immunoprecipitation, osteoclast differentiation assay (TRAP staining, bone resorption)\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP and Co-IP establish direct protein-DNA and protein-protein interactions, KD/OE with defined functional readout, single lab\",\n      \"pmids\": [\"25023277\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Binding of PQBP-1 to WBP11 (via PQBP-1's WW domain) allosterically reduces the binding affinity of PQBP-1 for U5-15kD (TXNL4A), demonstrating that PQBP-1's interactions with two spliceosomal partners are allosterically coupled.\",\n      \"method\": \"In vitro binding assays, NMR titration, isothermal titration calorimetry\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — quantitative in vitro binding with NMR and ITC, single lab, direct demonstration of allosteric modulation\",\n      \"pmids\": [\"27314904\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Yeast Dib1 (TXNL4A ortholog) functions to prevent premature spliceosome activation at the B-to-Bact transition. Temperature-sensitive dib1 mutants stall in vitro splicing prior to the first catalytic step and block assembly at the B complex. Dib1 exchanges readily in splicing extracts despite being a U5 snRNP component, indicating dynamic rather than static association.\",\n      \"method\": \"In vitro splicing assay with temperature-sensitive mutants, spliceosome assembly assay, protein exchange experiments in splicing extracts, circular dichroism\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro reconstitution splicing assay with defined mutants, assembly checkpoint identified, multiple biochemical approaches, single lab\",\n      \"pmids\": [\"29715471\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"TXNL4A lacks a classical nuclear localization signal and relies on PQBP-1 for nuclear import via a piggyback mechanism through the karyopherin β2 receptor. The PQBP-1 P244L missense mutation (X-linked intellectual disability) disrupts the PQBP-1–TXNL4A interaction and mislocalizes TXNL4A.\",\n      \"method\": \"Recombinant protein expression, in vitro binding assays, immunofluorescence microscopy in HeLa cells, PQBP-1 mutant analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro binding combined with direct subcellular localization imaging, disease mutation validation, multiple PQBP-1 variants tested, single lab with orthogonal methods\",\n      \"pmids\": [\"32041777\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Knockdown of Txnl4a in Xenopus embryos causes defects in cranial neural crest cell formation, establishing a direct role for TXNL4A in neural crest development underlying mandibulofacial dysostosis (Burn-McKeown syndrome). This parallels phenotypes from EFTUD2 and SNRPB knockdowns, pointing to a common spliceosomopathy mechanism.\",\n      \"method\": \"Morpholino-mediated knockdown in Xenopus embryos, neural crest marker analysis, craniofacial cartilage staining\",\n      \"journal\": \"Journal of developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct loss-of-function in vivo with defined developmental phenotype (neural crest depletion), single lab, single model organism\",\n      \"pmids\": [\"35893124\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Human Dim1 (TXNL4A) has peptidase activity with autocleavage, generating a thioredoxin-like core fragment. This truncated form retains peptidase activity. The autocleavage product corresponds to the dominant-negative fragment previously shown to cause G2 arrest.\",\n      \"method\": \"In vitro biochemical peptidase assay, autocleavage detection by SDS-PAGE/mass spectrometry\",\n      \"journal\": \"Chemical biology & drug design\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single biochemical assay, single lab, no mutagenesis to identify active-site residues, substrate not identified\",\n      \"pmids\": [\"17177886\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The ATPase Fap7 promotes formation of the rotated state of pre-40S ribosomes and releases Dim1 (TXNL4A ortholog) from nascent 40S subunits during ribosome maturation. This quality-control step links ribosome assembly to translocation competence; bypassing it causes reading-frame maintenance defects.\",\n      \"method\": \"Genetic epistasis, biochemical ribosome assembly assays, ATPase activity measurements, in vivo translation fidelity assay\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic and biochemical experiments, functional translation assay, mechanistic model validated by multiple orthogonal approaches, published in high-impact journal\",\n      \"pmids\": [\"28890337\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TXNL4A (U5-15kD/Dib1/Dim1) is an essential, evolutionarily conserved thioredoxin-fold protein that functions as a core component of the U5 snRNP and U4/U6·U5 tri-snRNP: it prevents premature spliceosome activation at the B-to-Bact transition by occupying a position adjacent to U6 snRNA and U5 loop I, is released during the B-to-Bact step, and is required for tri-snRNP assembly; its nuclear import depends on a piggyback mechanism via PQBP-1 and karyopherin β2; PQBP-1 binding to WBP11 allosterically modulates PQBP-1's affinity for TXNL4A; in parallel, TXNL4A binds c-Fos to repress NFATc1 transcription and osteoclastogenesis; in ribosome biogenesis, the Dim1 ortholog is released from pre-40S by the ATPase Fap7 as part of a quality-control translocation-like cycle; and biallelic loss-of-function mutations in TXNL4A—commonly a promoter deletion combined with a coding variant—cause Burn-McKeown syndrome by reducing TXNL4A expression and impairing splicing, with cranial neural crest cell formation as the critical developmental target.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TXNL4A (Dim1/Dib1/U5-15kD) is an essential, evolutionarily conserved thioredoxin-fold protein that functions as a core regulator of pre-mRNA splicing within the U5 snRNP and U4/U6·U5 tri-snRNP, where it acts as a checkpoint preventing premature spliceosome activation [#7, #10]. As a temperature-sensitive Dib1 mutant stalls in vitro splicing before the first catalytic step and blocks assembly at the B complex, while exchanging dynamically in splicing extracts, TXNL4A gates the B-to-Bact transition rather than serving as a static structural subunit [#10]; its depletion reduces U4/U6·U5 tri-snRNP assembly [#7]. Structurally, the protein adopts a thioredoxin fold defining a distinct branch of that superfamily, and removal of its C-terminal extension yields a dominant-negative form that arrests cells in G2 [#2]. TXNL4A engages the spliceosome-associated factor PQBP-1 through a defined 23-residue segment of PQBP-1's C-terminal domain [#3, #6], and because TXNL4A lacks a classical nuclear localization signal, it is imported into the nucleus by a piggyback mechanism on PQBP-1 via karyopherin β2; disease mutations in PQBP-1 disrupt this interaction and mislocalize TXNL4A [#11]. PQBP-1's affinity for TXNL4A is allosterically reduced when PQBP-1 binds WBP11 through its WW domain, coupling TXNL4A's handling to other spliceosomal interactions [#9]. Biallelic loss-of-function mutations in TXNL4A—typically a promoter deletion reducing expression combined with a coding variant—cause Burn-McKeown syndrome by impairing splicing, with cranial neural crest cell formation as the critical developmental target [#7, #12]. Beyond splicing, TXNL4A directly associates with c-Fos to block its binding to the NFATc1 promoter, repressing NFATc1 transcription and osteoclastogenesis [#8], and across species its orthologs are required for mitotic entry, chromosome segregation, and APC/C function [#0, #1].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Established that the Dim1 protein is essential and functionally conserved for cell cycle progression, answering whether a thioredoxin-like protein has a defined in vivo cellular requirement.\",\n      \"evidence\": \"Fission yeast genetic deletion and temperature-sensitive mutants with heterologous mouse complementation and histone H1 kinase assays\",\n      \"pmids\": [\"9182666\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the molecular activity producing G2 arrest\", \"Link to splicing not yet identified\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Connected dim1 function to APC/C-mediated ubiquitination, framing a possible mechanism for its mitotic phenotype.\",\n      \"evidence\": \"Synthetic-lethal screen, reciprocal Co-IP, sucrose gradient sedimentation and ubiquitination assays in S. pombe\",\n      \"pmids\": [\"10082519\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the APC/C link is direct or downstream of a splicing defect was not resolved\", \"No biochemical demonstration that Dim1 acts on APC/C components enzymatically\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Showed the protein is amenable to crystallographic study, a prerequisite for structural mechanism.\",\n      \"evidence\": \"Recombinant expression, purification and preliminary X-ray diffraction\",\n      \"pmids\": [\"10089325\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Preliminary crystallography only — no structure solved\", \"No functional inference possible\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Defined the thioredoxin fold and showed that a C-terminally truncated form is dominant-negative, linking structure to the cell cycle phenotype.\",\n      \"evidence\": \"NMR structural analysis, molecular modeling, alanine scanning, and overexpression cell-cycle assays\",\n      \"pmids\": [\"11015569\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Redox or catalytic role of the thioredoxin fold not demonstrated\", \"Mechanism by which the dominant-negative fragment arrests cells unresolved\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Reoriented the protein toward splicing by identifying exclusively splicing-related interaction partners, including PQBP-1 and hnRNP F.\",\n      \"evidence\": \"Yeast two-hybrid and reiterative screening, alanine scanning with structural interface mapping, mammalian co-expression and C. elegans RNAi\",\n      \"pmids\": [\"10873650\", \"11054566\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish where in the splicing cycle TXNL4A acts\", \"Functional consequence of each interaction not dissected\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Mapped the precise PQBP-1 segment binding TXNL4A and linked its disruption to X-linked mental retardation, giving the interaction disease relevance.\",\n      \"evidence\": \"Recombinant binding assays, NMR, and deletion/mutation mapping of PQBP-1 frameshift variants\",\n      \"pmids\": [\"20307692\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional readout of binding loss in cells not measured here\", \"Did not address nuclear import role\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identified TXNL4A loss-of-function as the cause of Burn-McKeown syndrome and tied reduced expression to impaired tri-snRNP assembly, unifying genetics with splicing mechanism.\",\n      \"evidence\": \"Patient genetics, promoter reporter and in vivo expression assays, and yeast Dib1 depletion with tri-snRNP assembly analysis\",\n      \"pmids\": [\"25434003\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Tissue specificity of the splicing defect not explained\", \"Which transcripts are misspliced in patients not defined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Revealed a splicing-independent transcriptional role in which TXNL4A represses NFATc1 and osteoclastogenesis by sequestering c-Fos.\",\n      \"evidence\": \"RNAi knockdown, overexpression, ChIP, Co-IP, and osteoclast differentiation assays\",\n      \"pmids\": [\"25023277\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; reciprocal validation of the c-Fos interaction limited\", \"Relationship between nuclear splicing pool and c-Fos-bound pool unclear\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Demonstrated that PQBP-1's two spliceosomal interactions are allosterically coupled, refining how TXNL4A handling is regulated.\",\n      \"evidence\": \"In vitro binding assays, NMR titration, and isothermal titration calorimetry\",\n      \"pmids\": [\"27314904\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological consequence of the allosteric coupling in cells not shown\", \"Single lab in vitro system\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Uncovered a role for the Dim1 ortholog in ribosome biogenesis, showing its release from pre-40S by the ATPase Fap7 is a translation-fidelity quality-control step.\",\n      \"evidence\": \"Genetic epistasis, biochemical ribosome assembly assays, ATPase measurements, and in vivo translation fidelity assays in yeast\",\n      \"pmids\": [\"28890337\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether human TXNL4A participates in ribosome biogenesis not tested\", \"Note: this ortholog activity may reflect a paralog (Dim1/DIMT1) rather than TXNL4A itself\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Defined the precise step of action: Dib1 prevents premature spliceosome activation at the B-to-Bact transition and associates dynamically rather than statically.\",\n      \"evidence\": \"In vitro splicing with temperature-sensitive mutants, assembly assays, protein exchange experiments, and circular dichroism\",\n      \"pmids\": [\"29715471\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular trigger for Dib1 release not identified\", \"Whether the thioredoxin fold has catalytic involvement in the checkpoint unresolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Explained how TXNL4A reaches the nucleus, showing a piggyback import mechanism on PQBP-1 via karyopherin β2 disrupted by disease mutations.\",\n      \"evidence\": \"Recombinant binding assays, immunofluorescence in HeLa cells, and analysis of PQBP-1 P244L and other variants\",\n      \"pmids\": [\"32041777\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether alternative import routes exist not addressed\", \"Quantitative contribution of import defect to disease phenotypes not measured\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Connected TXNL4A loss to the developmental target of Burn-McKeown syndrome by demonstrating a requirement in cranial neural crest formation.\",\n      \"evidence\": \"Morpholino knockdown in Xenopus embryos with neural crest marker and craniofacial cartilage analysis\",\n      \"pmids\": [\"35893124\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific misspliced transcripts driving the neural crest defect not identified\", \"Single model organism\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unknown whether the thioredoxin fold of TXNL4A carries an enzymatic activity relevant to its splicing checkpoint role, and what molecular signal triggers its release at the B-to-Bact transition.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No active-site mutagenesis tying putative catalytic residues to splicing\", \"Reported peptidase/autocleavage activity remains a single unconfirmed observation\", \"Trigger for Dib1 release during activation undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [11]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [7, 10]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [12]}\n    ],\n    \"complexes\": [\n      \"U5 snRNP\",\n      \"U4/U6·U5 tri-snRNP\"\n    ],\n    \"partners\": [\n      \"PQBP-1\",\n      \"WBP11\",\n      \"hnRNP F\",\n      \"c-Fos\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}