{"gene":"TRNAU1AP","run_date":"2026-04-28T21:43:00","timeline":{"discoveries":[{"year":1999,"finding":"SECp43 (TRNAU1AP) was identified as a novel RNA-binding protein that specifically associates with mammalian selenocysteine tRNA (tRNA[Ser]Sec), as demonstrated by affinity purification of tRNA(Sec) from HeLa cell extracts using anti-SECp43 antibody columns, and a 48-kDa interacting protein partner was also co-purified.","method":"Affinity purification with anti-SECp43 antibody column from native HeLa cell extracts, direct RNA sequencing and Northern blot analysis; degenerate PCR cloning; recombinant protein pulldown","journal":"RNA (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 2 — original discovery paper with multiple orthogonal methods (antibody column purification, sequencing, Northern blot, recombinant protein pulldown)","pmids":["10606267"],"is_preprint":false},{"year":2005,"finding":"SECp43 (TRNAU1AP) is required for the 2'-O-methylation at the wobble position (Um34) of tRNA[Ser]Sec; knockdown of SECp43 in NIH3T3 or TCMK-1 cells reduced Um34 methylation and consequently reduced glutathione peroxidase 1 expression. SECp43 forms a ternary complex with tRNA[Ser]Sec and SLA/LP, and removal of either protein affects the other's binding to tRNA[Ser]Sec. SECp43 (nuclear) promotes nuclear translocation of SLA (cytoplasmic) upon co-transfection.","method":"RNA interference knockdown, double knockdown, co-immunoprecipitation, subcellular fractionation, Northern/Western blot analysis, tRNA methylation assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (RNAi, co-IP, fractionation, methylation assay) in a single rigorous study with clear functional readouts","pmids":["16230358"],"is_preprint":false},{"year":2006,"finding":"SECp43 (TRNAU1AP) interacts with the selenocysteyl-tRNA[Ser]Sec–EFsec complex in vitro, promotes interaction between EFsec and SBP2 in vivo, increases selenocysteine incorporation and selenoprotein mRNA levels, and upon co-transfection with SLA/LP and SPS1, redistributes all three proteins to a predominantly nuclear localization, suggesting SECp43 orchestrates supramolecular complex assembly for selenoprotein biosynthesis.","method":"In vitro binding assay, co-immunoprecipitation in vivo, co-transfection with subcellular localization by immunofluorescence, selenoprotein expression assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — reciprocal in vitro and in vivo co-IP, localization experiments, and functional selenocysteine incorporation assay with multiple factors","pmids":["16508009"],"is_preprint":false},{"year":2017,"finding":"SECp43 (TRNAU1AP) is a globular protein comprising two RNA-binding domains, as revealed by small-angle X-ray scattering (SAXS). Two residues (K166 and P167) are required for SECp43 dimerization, identified via phage display. Additionally, BRET assays in mammalian cells showed that SECp43 forms oligomers and interacts with SEPSECS, SEPHS1, and SEPHS2 in the selenocysteine biosynthesis pathway; these interactions were confirmed by co-immunoprecipitation.","method":"Small-angle X-ray scattering (SAXS), bioluminescence resonance energy transfer (BRET) assay, co-immunoprecipitation, phage display, site-directed mutagenesis","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1-2 — SAXS structural analysis, mutagenesis identifying dimerization residues, and co-IP confirmation of interactions in a single study","pmids":["28414460"],"is_preprint":false},{"year":2015,"finding":"Conditional deletion of SECp43 (TRNAU1AP) exons 7+8 in mouse hepatocytes did not significantly alter selenoprotein expression, tRNA[Ser]Sec methylation (Um34), or liver histology; however, neuron-specific deletion of exons 7+8 impaired motor performance without affecting cerebellar development or cerebral selenoprotein expression. Constitutive deletion of exons 7+8 was embryonic lethal. Truncated Secp43 Δ7,8 mRNA was upregulated in mutant livers, suggesting auto-regulation of Secp43 mRNA abundance.","method":"Conditional knockout mouse models (Cre-lox), 75Se metabolic labeling, Western blot, enzymatic activity assay, tRNA methylation analysis, behavioral motor testing","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 — in vivo conditional knockout with multiple biochemical and functional readouts, including embryonic lethality of full deletion","pmids":["26043259"],"is_preprint":false},{"year":2018,"finding":"Knockdown of Trnau1ap (TRNAU1AP/SECp43) in NIH3T3, JEG-3, and Bewo cells reduced selenoprotein expression and inhibited cell proliferation and migration, with attenuation of Akt phosphorylation in the PI3K/Akt signaling pathway.","method":"Lentiviral shRNA knockdown, CCK-8 proliferation assay, wound scratch migration assay, Western blot for PI3K/Akt pathway components","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 — single lab, loss-of-function with phenotypic readout and pathway placement, but limited mechanistic depth","pmids":["29758194"],"is_preprint":false},{"year":2016,"finding":"Knockdown of Trnau1ap (TRNAU1AP/SECp43) in cardiomyocyte-like H9c2 cells reduced expression of selenoproteins (glutathione peroxidase, thioredoxin reductase, selenoprotein K), inhibited proliferation, and induced apoptosis with increased Bax and decreased Bcl-2 expression and activation of the PI3K/Akt pathway; overexpression had opposite effects.","method":"siRNA knockdown, overexpression plasmid, MTT assay, PCNA detection, annexin V assay, caspase-3 activity assay, Western blot","journal":"Molecular medicine reports","confidence":"Medium","confidence_rationale":"Tier 3 — single lab with both gain- and loss-of-function and multiple readouts, but pathway placement is correlative","pmids":["28101579"],"is_preprint":false},{"year":2024,"finding":"TRNAU1AP was found to modulate hundreds of endogenous alternative splicing events when tethered to splicing reporters; enhanced CLIP and affinity purification-mass spectrometry confirmed its direct RNA-binding activity and splicing regulatory role, establishing an unexpected function for TRNAU1AP as a splicing regulator beyond its known role in selenocysteine incorporation.","method":"Tethered function luciferase-based splicing reporter assay, enhanced CLIP (eCLIP), RNA-seq, affinity purification-mass spectrometry (AP-MS)","journal":"Nature biotechnology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods (tethering assay, eCLIP, RNA-seq, AP-MS) with endogenous splicing validation","pmids":["38168984"],"is_preprint":false}],"current_model":"TRNAU1AP (SECp43) is an RNA-binding protein with two RNA recognition motifs that specifically binds tRNA[Ser]Sec, forms oligomers and supramolecular complexes with SLA/LP, EFsec, SBP2, SEPSECS, SEPHS1, and SEPHS2 to orchestrate selenocysteine biosynthesis and incorporation at UGA codons, promotes Um34 methylation of tRNA[Ser]Sec, regulates nuclear-cytoplasmic shuttling of selenocysteine synthesis factors, is essential for embryonic viability, and—unexpectedly—also directly modulates hundreds of endogenous alternative splicing events as an RNA-binding protein."},"narrative":{"teleology":[{"year":1999,"claim":"The identification of TRNAU1AP as a specific tRNA[Ser]Sec-binding protein established the existence of a dedicated accessory factor for selenocysteine biology beyond the core translation machinery.","evidence":"Affinity purification with anti-SECp43 antibody from HeLa extracts followed by RNA sequencing and Northern blot","pmids":["10606267"],"confidence":"High","gaps":["Identity of the co-purified 48-kDa partner was not determined","Direct vs. indirect RNA binding not resolved","No functional assay for selenoprotein synthesis included"]},{"year":2005,"claim":"Demonstrating that TRNAU1AP is required for Um34 methylation of tRNA[Ser]Sec and forms a ternary complex with SLA/LP revealed its mechanistic role in tRNA maturation and factor recruitment, explaining how it controls stress-related selenoprotein expression.","evidence":"RNAi knockdown in NIH3T3 and TCMK-1 cells with tRNA methylation assay, co-IP, and subcellular fractionation","pmids":["16230358"],"confidence":"High","gaps":["The methyltransferase catalyzing Um34 was not identified in this context","Whether TRNAU1AP directly contacts the methyltransferase is unknown","Mechanism of nuclear import promotion for SLA/LP not defined"]},{"year":2006,"claim":"Showing that TRNAU1AP promotes EFsec–SBP2 interaction and increases selenocysteine incorporation established it as a scaffold that organizes the selenoprotein translation machinery and controls subcellular distribution of pathway components.","evidence":"In vitro binding assay, co-IP in vivo, co-transfection with immunofluorescence, selenoprotein expression assays","pmids":["16508009"],"confidence":"High","gaps":["Stoichiometry of the supramolecular complex not determined","Whether scaffold function requires RNA binding is unclear","No reconstitution of selenocysteine incorporation with purified components"]},{"year":2015,"claim":"Conditional knockout studies revealed that constitutive loss of TRNAU1AP is embryonic lethal and neuron-specific deletion impairs motor function, yet hepatocyte-specific deletion does not alter selenoprotein levels, exposing unexplained tissue-specific dependencies.","evidence":"Cre-lox conditional knockout mice with 75Se metabolic labeling, Western blot, tRNA methylation analysis, behavioral testing","pmids":["26043259"],"confidence":"High","gaps":["Truncated Δ7,8 protein product may retain partial function, confounding interpretation of liver results","Molecular basis of neuronal vulnerability not identified","Cause of embryonic lethality (selenoprotein-dependent or independent) not resolved"]},{"year":2016,"claim":"Loss- and gain-of-function experiments in cardiomyocyte-like cells linked TRNAU1AP to cell survival via selenoprotein-dependent anti-apoptotic signaling, extending its functional relevance beyond hepatocytes and neurons.","evidence":"siRNA knockdown and overexpression in H9c2 cells with annexin V apoptosis assay, caspase-3 activity, and Western blot for PI3K/Akt and Bcl-2 family","pmids":["28101579"],"confidence":"Medium","gaps":["PI3K/Akt pathway activation is correlative; direct mechanism linking TRNAU1AP to Akt not shown","Effects not distinguished from general selenoprotein deficiency","Single cell line and single lab"]},{"year":2017,"claim":"SAXS and mutagenesis defined TRNAU1AP as a two-RRM globular protein that dimerizes via K166/P167 and interacts with SEPSECS, SEPHS1, and SEPHS2, providing the first structural framework for its scaffold function.","evidence":"SAXS, phage display for dimerization interface, BRET in mammalian cells, co-IP","pmids":["28414460"],"confidence":"High","gaps":["No high-resolution structure of the full-length protein or its RNA-bound state","Functional consequence of dimerization disruption on selenoprotein synthesis not tested in cells","Whether dimerization is required for splicing function is unknown"]},{"year":2024,"claim":"The discovery that TRNAU1AP modulates hundreds of alternative splicing events via direct RNA binding fundamentally expanded its functional repertoire beyond selenocysteine biology.","evidence":"Tethered-function splicing reporters, eCLIP, RNA-seq, and AP-MS in human cells","pmids":["38168984"],"confidence":"High","gaps":["RNA sequence/structure determinants of splicing targets not defined","Whether splicing and selenocysteine functions are coordinated or independent is unknown","Physiological significance of splicing regulation in vivo not tested"]},{"year":null,"claim":"It remains unknown how TRNAU1AP's dual functions in selenocysteine biosynthesis and alternative splicing are coordinated, what determines its tissue-specific essentiality, and what its high-resolution RNA-bound structure looks like.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution co-crystal or cryo-EM structure with tRNA[Ser]Sec or mRNA substrates","Mechanistic basis of embryonic lethality (selenoprotein vs. splicing vs. both) unresolved","Whether splicing regulation contributes to neuronal motor phenotype is untested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[0,1,7]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[2,3]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[1,2]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[1,2]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[1,2,3]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[7]}],"complexes":["selenocysteine biosynthesis complex"],"partners":["SECP43-SLA/LP (SLA)","EEFSEC","SECISBP2","SEPSECS","SEPHS1","SEPHS2"],"other_free_text":[]},"mechanistic_narrative":"TRNAU1AP (SECp43) is an RNA-binding protein that orchestrates selenocysteine biosynthesis and incorporation by assembling supramolecular complexes of selenocysteine pathway factors and regulating their subcellular localization. It specifically binds tRNA[Ser]Sec and forms ternary and higher-order complexes with SLA/LP, EFsec, SBP2, SEPSECS, SEPHS1, and SEPHS2, promoting the 2'-O-methylation (Um34) of tRNA[Ser]Sec required for stress-related selenoprotein expression and facilitating nuclear-cytoplasmic shuttling of pathway components [PMID:10606267, PMID:16230358, PMID:16508009, PMID:28414460]. Constitutive deletion in mice is embryonic lethal and neuron-specific loss impairs motor function, establishing essential roles in development and neuronal physiology [PMID:26043259]. Beyond selenoprotein synthesis, TRNAU1AP directly modulates hundreds of endogenous alternative splicing events, as demonstrated by eCLIP, tethered-function assays, and RNA-seq [PMID:38168984]."},"prefetch_data":{"uniprot":{"accession":"Q9NX07","full_name":"tRNA selenocysteine 1-associated protein 1","aliases":["SECp43","tRNA selenocysteine-associated protein 1"],"length_aa":287,"mass_kda":32.5,"function":"Involved in the early steps of selenocysteine biosynthesis and tRNA(Sec) charging to the later steps resulting in the cotranslational incorporation of selenocysteine into selenoproteins (PubMed:16508009). Stabilizes the SECISBP2, EEFSEC and tRNA(Sec) complex (PubMed:16508009). May be involved in the methylation of tRNA(Sec) (PubMed:16508009). Enhances efficiency of selenoproteins synthesis (PubMed:16508009)","subcellular_location":"Nucleus; Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q9NX07/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TRNAU1AP","classification":"Not Classified","n_dependent_lines":352,"n_total_lines":1208,"dependency_fraction":0.2913907284768212},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/TRNAU1AP","total_profiled":1310},"omim":[{"mim_id":"619597","title":"tRNA SELENOCYSTEINE 1-ASSOCIATED PROTEIN 1; TRNAU1AP","url":"https://www.omim.org/entry/619597"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/TRNAU1AP"},"hgnc":{"alias_symbol":["SECP43","FLJ20503"],"prev_symbol":["TRSPAP1"]},"alphafold":{"accession":"Q9NX07","domains":[{"cath_id":"3.30.70.330","chopping":"2-82","consensus_level":"high","plddt":94.0532,"start":2,"end":82},{"cath_id":"3.30.70.330","chopping":"95-173","consensus_level":"high","plddt":93.8489,"start":95,"end":173}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NX07","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NX07-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NX07-F1-predicted_aligned_error_v6.png","plddt_mean":75.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TRNAU1AP","jax_strain_url":"https://www.jax.org/strain/search?query=TRNAU1AP"},"sequence":{"accession":"Q9NX07","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9NX07.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9NX07/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NX07"}},"corpus_meta":[{"pmid":"17553827","id":"PMC_17553827","title":"The selenoproteome exhibits widely varying, tissue-specific dependence on selenoprotein P for selenium supply.","date":"2007","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/17553827","citation_count":145,"is_preprint":false},{"pmid":"16508009","id":"PMC_16508009","title":"Supramolecular complexes mediate selenocysteine incorporation in vivo.","date":"2006","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/16508009","citation_count":119,"is_preprint":false},{"pmid":"28977470","id":"PMC_28977470","title":"The PRMT5/WDR77 complex regulates alternative splicing through ZNF326 in breast cancer.","date":"2017","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/28977470","citation_count":72,"is_preprint":false},{"pmid":"16230358","id":"PMC_16230358","title":"Evidence for direct roles of two additional factors, SECp43 and soluble liver antigen, in the selenoprotein synthesis machinery.","date":"2005","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16230358","citation_count":66,"is_preprint":false},{"pmid":"10606267","id":"PMC_10606267","title":"Identification of a protein component of a mammalian tRNA(Sec) complex implicated in the decoding of UGA as selenocysteine.","date":"1999","source":"RNA (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/10606267","citation_count":34,"is_preprint":false},{"pmid":"16766053","id":"PMC_16766053","title":"Identification of Leishmania selenoproteins and SECIS element.","date":"2006","source":"Molecular and biochemical parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/16766053","citation_count":32,"is_preprint":false},{"pmid":"20659579","id":"PMC_20659579","title":"Zebrafish (Danio rerio) vary by strain and sex in their behavioral and transcriptional responses to selenium supplementation.","date":"2010","source":"Comparative biochemistry and physiology. Part A, Molecular & integrative physiology","url":"https://pubmed.ncbi.nlm.nih.gov/20659579","citation_count":30,"is_preprint":false},{"pmid":"32172502","id":"PMC_32172502","title":"Selenium Deficiency-Induced Damage and Altered Expression of Mitochondrial Biogenesis Markers in the Kidneys of Mice.","date":"2020","source":"Biological trace element research","url":"https://pubmed.ncbi.nlm.nih.gov/32172502","citation_count":25,"is_preprint":false},{"pmid":"28414460","id":"PMC_28414460","title":"Analysis of Novel Interactions between Components of the Selenocysteine Biosynthesis Pathway, SEPHS1, SEPHS2, SEPSECS, and SECp43.","date":"2017","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/28414460","citation_count":18,"is_preprint":false},{"pmid":"24817701","id":"PMC_24817701","title":"Adjustments, extinction, and remains of selenocysteine incorporation machinery in the nematode lineage.","date":"2014","source":"RNA (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/24817701","citation_count":18,"is_preprint":false},{"pmid":"38168984","id":"PMC_38168984","title":"Large-scale evaluation of the ability of RNA-binding proteins to activate exon inclusion.","date":"2024","source":"Nature biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/38168984","citation_count":18,"is_preprint":false},{"pmid":"32065787","id":"PMC_32065787","title":"Novel somatic alterations underlie Chinese papillary thyroid carcinoma.","date":"2020","source":"Cancer biomarkers : section A of Disease markers","url":"https://pubmed.ncbi.nlm.nih.gov/32065787","citation_count":18,"is_preprint":false},{"pmid":"33895963","id":"PMC_33895963","title":"Selenium Deficiency Leads to Changes in Renal Fibrosis Marker Proteins and Wnt/β-Catenin Signaling Pathway Components.","date":"2021","source":"Biological trace element research","url":"https://pubmed.ncbi.nlm.nih.gov/33895963","citation_count":14,"is_preprint":false},{"pmid":"26043259","id":"PMC_26043259","title":"Expression of Selenoproteins Is Maintained in Mice Carrying Mutations in SECp43, the tRNA Selenocysteine 1 Associated Protein (Trnau1ap).","date":"2015","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/26043259","citation_count":12,"is_preprint":false},{"pmid":"24854764","id":"PMC_24854764","title":"Effects of acclimation salinity on the expression of selenoproteins in the tilapia, Oreochromis mossambicus.","date":"2014","source":"Journal of trace elements in medicine and biology : organ of the Society for Minerals and Trace Elements (GMS)","url":"https://pubmed.ncbi.nlm.nih.gov/24854764","citation_count":11,"is_preprint":false},{"pmid":"29758194","id":"PMC_29758194","title":"Knockdown of Trnau1ap inhibits the proliferation and migration of NIH3T3, JEG-3 and Bewo cells via the PI3K/Akt signaling pathway.","date":"2018","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/29758194","citation_count":8,"is_preprint":false},{"pmid":"28101579","id":"PMC_28101579","title":"Role of tRNA selenocysteine 1 associated protein 1 in the proliferation and apoptosis of cardiomyocyte‑like H9c2 cells.","date":"2016","source":"Molecular medicine reports","url":"https://pubmed.ncbi.nlm.nih.gov/28101579","citation_count":8,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":9722,"output_tokens":2391,"usd":0.032516},"stage2":{"model":"claude-opus-4-6","input_tokens":5673,"output_tokens":2132,"usd":0.122497},"total_usd":0.155013,"stage1_batch_id":"msgbatch_01RPbVc9PDH9zQmYK5Hs6srm","stage2_batch_id":"msgbatch_01JVbVLzeKN2yVrsGp3zC8aM","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1999,\n      \"finding\": \"SECp43 (TRNAU1AP) was identified as a novel RNA-binding protein that specifically associates with mammalian selenocysteine tRNA (tRNA[Ser]Sec), as demonstrated by affinity purification of tRNA(Sec) from HeLa cell extracts using anti-SECp43 antibody columns, and a 48-kDa interacting protein partner was also co-purified.\",\n      \"method\": \"Affinity purification with anti-SECp43 antibody column from native HeLa cell extracts, direct RNA sequencing and Northern blot analysis; degenerate PCR cloning; recombinant protein pulldown\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — original discovery paper with multiple orthogonal methods (antibody column purification, sequencing, Northern blot, recombinant protein pulldown)\",\n      \"pmids\": [\"10606267\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"SECp43 (TRNAU1AP) is required for the 2'-O-methylation at the wobble position (Um34) of tRNA[Ser]Sec; knockdown of SECp43 in NIH3T3 or TCMK-1 cells reduced Um34 methylation and consequently reduced glutathione peroxidase 1 expression. SECp43 forms a ternary complex with tRNA[Ser]Sec and SLA/LP, and removal of either protein affects the other's binding to tRNA[Ser]Sec. SECp43 (nuclear) promotes nuclear translocation of SLA (cytoplasmic) upon co-transfection.\",\n      \"method\": \"RNA interference knockdown, double knockdown, co-immunoprecipitation, subcellular fractionation, Northern/Western blot analysis, tRNA methylation assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (RNAi, co-IP, fractionation, methylation assay) in a single rigorous study with clear functional readouts\",\n      \"pmids\": [\"16230358\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"SECp43 (TRNAU1AP) interacts with the selenocysteyl-tRNA[Ser]Sec–EFsec complex in vitro, promotes interaction between EFsec and SBP2 in vivo, increases selenocysteine incorporation and selenoprotein mRNA levels, and upon co-transfection with SLA/LP and SPS1, redistributes all three proteins to a predominantly nuclear localization, suggesting SECp43 orchestrates supramolecular complex assembly for selenoprotein biosynthesis.\",\n      \"method\": \"In vitro binding assay, co-immunoprecipitation in vivo, co-transfection with subcellular localization by immunofluorescence, selenoprotein expression assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal in vitro and in vivo co-IP, localization experiments, and functional selenocysteine incorporation assay with multiple factors\",\n      \"pmids\": [\"16508009\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SECp43 (TRNAU1AP) is a globular protein comprising two RNA-binding domains, as revealed by small-angle X-ray scattering (SAXS). Two residues (K166 and P167) are required for SECp43 dimerization, identified via phage display. Additionally, BRET assays in mammalian cells showed that SECp43 forms oligomers and interacts with SEPSECS, SEPHS1, and SEPHS2 in the selenocysteine biosynthesis pathway; these interactions were confirmed by co-immunoprecipitation.\",\n      \"method\": \"Small-angle X-ray scattering (SAXS), bioluminescence resonance energy transfer (BRET) assay, co-immunoprecipitation, phage display, site-directed mutagenesis\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — SAXS structural analysis, mutagenesis identifying dimerization residues, and co-IP confirmation of interactions in a single study\",\n      \"pmids\": [\"28414460\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Conditional deletion of SECp43 (TRNAU1AP) exons 7+8 in mouse hepatocytes did not significantly alter selenoprotein expression, tRNA[Ser]Sec methylation (Um34), or liver histology; however, neuron-specific deletion of exons 7+8 impaired motor performance without affecting cerebellar development or cerebral selenoprotein expression. Constitutive deletion of exons 7+8 was embryonic lethal. Truncated Secp43 Δ7,8 mRNA was upregulated in mutant livers, suggesting auto-regulation of Secp43 mRNA abundance.\",\n      \"method\": \"Conditional knockout mouse models (Cre-lox), 75Se metabolic labeling, Western blot, enzymatic activity assay, tRNA methylation analysis, behavioral motor testing\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo conditional knockout with multiple biochemical and functional readouts, including embryonic lethality of full deletion\",\n      \"pmids\": [\"26043259\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Knockdown of Trnau1ap (TRNAU1AP/SECp43) in NIH3T3, JEG-3, and Bewo cells reduced selenoprotein expression and inhibited cell proliferation and migration, with attenuation of Akt phosphorylation in the PI3K/Akt signaling pathway.\",\n      \"method\": \"Lentiviral shRNA knockdown, CCK-8 proliferation assay, wound scratch migration assay, Western blot for PI3K/Akt pathway components\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single lab, loss-of-function with phenotypic readout and pathway placement, but limited mechanistic depth\",\n      \"pmids\": [\"29758194\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Knockdown of Trnau1ap (TRNAU1AP/SECp43) in cardiomyocyte-like H9c2 cells reduced expression of selenoproteins (glutathione peroxidase, thioredoxin reductase, selenoprotein K), inhibited proliferation, and induced apoptosis with increased Bax and decreased Bcl-2 expression and activation of the PI3K/Akt pathway; overexpression had opposite effects.\",\n      \"method\": \"siRNA knockdown, overexpression plasmid, MTT assay, PCNA detection, annexin V assay, caspase-3 activity assay, Western blot\",\n      \"journal\": \"Molecular medicine reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single lab with both gain- and loss-of-function and multiple readouts, but pathway placement is correlative\",\n      \"pmids\": [\"28101579\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"TRNAU1AP was found to modulate hundreds of endogenous alternative splicing events when tethered to splicing reporters; enhanced CLIP and affinity purification-mass spectrometry confirmed its direct RNA-binding activity and splicing regulatory role, establishing an unexpected function for TRNAU1AP as a splicing regulator beyond its known role in selenocysteine incorporation.\",\n      \"method\": \"Tethered function luciferase-based splicing reporter assay, enhanced CLIP (eCLIP), RNA-seq, affinity purification-mass spectrometry (AP-MS)\",\n      \"journal\": \"Nature biotechnology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (tethering assay, eCLIP, RNA-seq, AP-MS) with endogenous splicing validation\",\n      \"pmids\": [\"38168984\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TRNAU1AP (SECp43) is an RNA-binding protein with two RNA recognition motifs that specifically binds tRNA[Ser]Sec, forms oligomers and supramolecular complexes with SLA/LP, EFsec, SBP2, SEPSECS, SEPHS1, and SEPHS2 to orchestrate selenocysteine biosynthesis and incorporation at UGA codons, promotes Um34 methylation of tRNA[Ser]Sec, regulates nuclear-cytoplasmic shuttling of selenocysteine synthesis factors, is essential for embryonic viability, and—unexpectedly—also directly modulates hundreds of endogenous alternative splicing events as an RNA-binding protein.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"TRNAU1AP (SECp43) is an RNA-binding protein that orchestrates selenocysteine biosynthesis and incorporation by assembling supramolecular complexes of selenocysteine pathway factors and regulating their subcellular localization. It specifically binds tRNA[Ser]Sec and forms ternary and higher-order complexes with SLA/LP, EFsec, SBP2, SEPSECS, SEPHS1, and SEPHS2, promoting the 2'-O-methylation (Um34) of tRNA[Ser]Sec required for stress-related selenoprotein expression and facilitating nuclear-cytoplasmic shuttling of pathway components [PMID:10606267, PMID:16230358, PMID:16508009, PMID:28414460]. Constitutive deletion in mice is embryonic lethal and neuron-specific loss impairs motor function, establishing essential roles in development and neuronal physiology [PMID:26043259]. Beyond selenoprotein synthesis, TRNAU1AP directly modulates hundreds of endogenous alternative splicing events, as demonstrated by eCLIP, tethered-function assays, and RNA-seq [PMID:38168984].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"The identification of TRNAU1AP as a specific tRNA[Ser]Sec-binding protein established the existence of a dedicated accessory factor for selenocysteine biology beyond the core translation machinery.\",\n      \"evidence\": \"Affinity purification with anti-SECp43 antibody from HeLa extracts followed by RNA sequencing and Northern blot\",\n      \"pmids\": [\"10606267\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the co-purified 48-kDa partner was not determined\", \"Direct vs. indirect RNA binding not resolved\", \"No functional assay for selenoprotein synthesis included\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Demonstrating that TRNAU1AP is required for Um34 methylation of tRNA[Ser]Sec and forms a ternary complex with SLA/LP revealed its mechanistic role in tRNA maturation and factor recruitment, explaining how it controls stress-related selenoprotein expression.\",\n      \"evidence\": \"RNAi knockdown in NIH3T3 and TCMK-1 cells with tRNA methylation assay, co-IP, and subcellular fractionation\",\n      \"pmids\": [\"16230358\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The methyltransferase catalyzing Um34 was not identified in this context\", \"Whether TRNAU1AP directly contacts the methyltransferase is unknown\", \"Mechanism of nuclear import promotion for SLA/LP not defined\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Showing that TRNAU1AP promotes EFsec–SBP2 interaction and increases selenocysteine incorporation established it as a scaffold that organizes the selenoprotein translation machinery and controls subcellular distribution of pathway components.\",\n      \"evidence\": \"In vitro binding assay, co-IP in vivo, co-transfection with immunofluorescence, selenoprotein expression assays\",\n      \"pmids\": [\"16508009\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of the supramolecular complex not determined\", \"Whether scaffold function requires RNA binding is unclear\", \"No reconstitution of selenocysteine incorporation with purified components\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Conditional knockout studies revealed that constitutive loss of TRNAU1AP is embryonic lethal and neuron-specific deletion impairs motor function, yet hepatocyte-specific deletion does not alter selenoprotein levels, exposing unexplained tissue-specific dependencies.\",\n      \"evidence\": \"Cre-lox conditional knockout mice with 75Se metabolic labeling, Western blot, tRNA methylation analysis, behavioral testing\",\n      \"pmids\": [\"26043259\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Truncated Δ7,8 protein product may retain partial function, confounding interpretation of liver results\", \"Molecular basis of neuronal vulnerability not identified\", \"Cause of embryonic lethality (selenoprotein-dependent or independent) not resolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Loss- and gain-of-function experiments in cardiomyocyte-like cells linked TRNAU1AP to cell survival via selenoprotein-dependent anti-apoptotic signaling, extending its functional relevance beyond hepatocytes and neurons.\",\n      \"evidence\": \"siRNA knockdown and overexpression in H9c2 cells with annexin V apoptosis assay, caspase-3 activity, and Western blot for PI3K/Akt and Bcl-2 family\",\n      \"pmids\": [\"28101579\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"PI3K/Akt pathway activation is correlative; direct mechanism linking TRNAU1AP to Akt not shown\", \"Effects not distinguished from general selenoprotein deficiency\", \"Single cell line and single lab\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"SAXS and mutagenesis defined TRNAU1AP as a two-RRM globular protein that dimerizes via K166/P167 and interacts with SEPSECS, SEPHS1, and SEPHS2, providing the first structural framework for its scaffold function.\",\n      \"evidence\": \"SAXS, phage display for dimerization interface, BRET in mammalian cells, co-IP\",\n      \"pmids\": [\"28414460\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No high-resolution structure of the full-length protein or its RNA-bound state\", \"Functional consequence of dimerization disruption on selenoprotein synthesis not tested in cells\", \"Whether dimerization is required for splicing function is unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"The discovery that TRNAU1AP modulates hundreds of alternative splicing events via direct RNA binding fundamentally expanded its functional repertoire beyond selenocysteine biology.\",\n      \"evidence\": \"Tethered-function splicing reporters, eCLIP, RNA-seq, and AP-MS in human cells\",\n      \"pmids\": [\"38168984\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"RNA sequence/structure determinants of splicing targets not defined\", \"Whether splicing and selenocysteine functions are coordinated or independent is unknown\", \"Physiological significance of splicing regulation in vivo not tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unknown how TRNAU1AP's dual functions in selenocysteine biosynthesis and alternative splicing are coordinated, what determines its tissue-specific essentiality, and what its high-resolution RNA-bound structure looks like.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution co-crystal or cryo-EM structure with tRNA[Ser]Sec or mRNA substrates\", \"Mechanistic basis of embryonic lethality (selenoprotein vs. splicing vs. both) unresolved\", \"Whether splicing regulation contributes to neuronal motor phenotype is untested\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [0, 1, 7]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [2, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [1, 2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [1, 2, 3]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [7]}\n    ],\n    \"complexes\": [\n      \"selenocysteine biosynthesis complex\"\n    ],\n    \"partners\": [\n      \"SECP43-SLA/LP (SLA)\",\n      \"EEFSEC\",\n      \"SECISBP2\",\n      \"SEPSECS\",\n      \"SEPHS1\",\n      \"SEPHS2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}