{"gene":"TRMU","run_date":"2026-06-10T10:51:56","timeline":{"discoveries":[{"year":2004,"finding":"Mouse TRMU protein localizes to mitochondria, as demonstrated by immunofluorescence of NIH3T3 cells expressing TRMU-GFP fusion protein, establishing it as a mitochondrial tRNA-modifying enzyme homologous to bacterial TrmU.","method":"Immunofluorescence microscopy of TRMU-GFP fusion protein in NIH3T3 cells","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct localization experiment with GFP fusion, replicated in human cells (PMID:16513084), single lab","pmids":["14746906"],"is_preprint":false},{"year":2006,"finding":"Human TRMU protein localizes to mitochondria, demonstrated by immunofluorescence of human 143B cells expressing TRMU-GFP fusion protein.","method":"Immunofluorescence microscopy of TRMU-GFP fusion protein in human 143B cells","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct localization experiment, consistent with mouse data (PMID:14746906), single lab","pmids":["16513084"],"is_preprint":false},{"year":2006,"finding":"A homozygous missense mutation (A10S) in TRMU reduces steady-state levels of mitochondrial tRNAs and impairs mitochondrial protein synthesis, acting as a nuclear modifier that aggravates mitochondrial dysfunction associated with the 12S rRNA A1555G mutation to cause deafness. The A10S mutation does not affect mitochondrial import of TRMU.","method":"Genotyping, functional analysis of mitochondrial tRNA levels and protein synthesis in patient-derived cells, import assay","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal biochemical methods (tRNA quantification, protein synthesis, import assay) in patient cells, replicated and extended by subsequent studies","pmids":["16826519"],"is_preprint":false},{"year":2007,"finding":"In yeast S. cerevisiae, deletion of MTO2 (the yeast ortholog of TRMU) causes marked decreases in steady-state levels of mitochondrial tRNAs (tRNALys, tRNAGlu, tRNAGln, tRNALeu, tRNAGly, tRNAMet), impairs aminoacylation of tRNALys and tRNALeu, and reduces steady-state levels of mitochondrial mRNAs (CYTB, COX1, COX2, COX3, ATP6), demonstrating that tRNA modification by MTO2 is required for mitochondrial RNA stability.","method":"Northern blot analysis of mitochondrial tRNA and mRNA levels; aminoacylation assays in mto2 null yeast strains","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro assays (aminoacylation) plus multiple RNA quantification methods in genetic knockout, single lab but multiple orthogonal methods","pmids":["17706197"],"is_preprint":false},{"year":2009,"finding":"TRMU encodes a mitochondria-specific tRNA-modifying enzyme (tRNA 5-methylaminomethyl-2-thiouridylate methyltransferase) responsible for 2-thiouridylation of mitochondrial tRNAs; mutations in TRMU cause markedly reduced 2-thiouridylation levels of mitochondrial tRNAs and result in acute infantile liver failure with combined respiratory chain deficiency without mtDNA depletion.","method":"Homozygosity mapping, mutation identification, biochemical measurement of 2-thiouridylation levels in patient tissues","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct biochemical measurement of enzymatic product (2-thiouridylation) in patient cells, 13 unrelated patients, replicated across multiple studies","pmids":["19732863"],"is_preprint":false},{"year":2011,"finding":"Loss of MTU1 (TRMU) in patient fibroblasts and HEK293 cells severely reduces 2-thiolation of mitochondrial tRNALys, tRNAGlu, and tRNAGln but does not impair overall mitochondrial translation at normal steady-state tRNA levels, indicating the 2-thiouridylase function is dispensable for translation under these conditions. The only respiratory chain abnormality observed was accumulation of a Complex II assembly intermediate without affecting fully assembled enzyme levels.","method":"Immunoblotting, siRNA knockdown, analysis of mitochondrial translation, respiratory chain enzyme assays in patient fibroblasts and HEK293 cells","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (immunoblot, siRNA KD, translation assay, respiratory chain assay) in two cell systems, single lab; contradicts some prior assumptions","pmids":["21890497"],"is_preprint":false},{"year":2013,"finding":"In yeast, deletion of the nuclear modifier gene MTO2 suppresses aminoglycoside-sensitivity of mitochondrial 15S rRNA C1477G mutation; the double mutant (mto2/C1477G) shows decreased oxygen consumption but compensates through upregulation of glycolytic genes (HXK2, PFK1, PYK1), providing energy via glycolysis.","method":"Genetic epistasis analysis, oxygen consumption measurements, gene expression analysis, glycolytic inhibitor treatment in S. cerevisiae","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with multiple functional readouts, single lab","pmids":["24339937"],"is_preprint":false},{"year":2016,"finding":"Liver-specific knockout of Mtu1 in mice causes loss of 2-thiolation in mitochondrial tRNAs, leading to marked impairment of mitochondrial translation, disruption of mitochondrial membrane integrity, and broad decrease in respiratory complex activities in hepatocytes, demonstrating that Mtu1-dependent 2-thiolation of mt-tRNA is indispensable for mitochondrial translation in vivo.","method":"Liver-specific Mtu1 knockout mouse model, mass spectrometry of tRNA modifications, mitochondrial translation assay, respiratory complex activity assays, electron microscopy","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — genetic knockout in vivo with multiple orthogonal mechanistic readouts; directly demonstrates requirement for translation in vivo","pmids":["27689697"],"is_preprint":false},{"year":2016,"finding":"Reduced TRMU expression in HEI-OC-1 hair-cell-like cells increases mitochondrial dysfunction and reactive oxygen species (ROS) levels after neomycin treatment, leading to increased apoptosis; N-acetylcysteine rescued the mitochondrial dysfunction and apoptosis, indicating TRMU regulates mitochondrial function and ROS levels in this context.","method":"siRNA knockdown of TRMU in HEI-OC-1 cells, ROS measurement, mitochondrial function assays, cell viability/apoptosis assays, N-acetylcysteine rescue experiment","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — siRNA KD with multiple functional readouts and chemical rescue, single lab","pmids":["27405449"],"is_preprint":false},{"year":2017,"finding":"The TRMU A10S mutation introduces a Ser10 dynamic electrostatic interaction with Lys106 in the catalytic domain (shown by molecular dynamics simulations), reduces TRMU protein levels, reduces thermal stability of the TRMU protein, and causes marked decreases in 2-thiouridine modification of U34 of tRNALys, tRNAGlu, and tRNAGln while mildly increasing aminoacylation efficiency of tRNAs. The defective 2-thiouridine modification worsens mitochondrial translation impairment associated with m.1555A>G mutation, reducing respiratory chain activities, ATP production, and elevating ROS.","method":"Molecular dynamics simulation, Western blotting, thermal shift assay, tRNA modification analysis (2-thiouridine levels), aminoacylation assays, mitochondrial translation and respiration measurements","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — multiple orthogonal biochemical and structural methods including in vitro enzymatic assays and mutagenesis analysis, single lab","pmids":["28049726"],"is_preprint":false},{"year":2017,"finding":"Expression of TRMU is regulated by microRNAs induced by retrograde mitochondrial signals (ROS and Ca2+) in cybrid models of mtDNA diseases, altering the modification status of mitochondrial tRNAs as part of a cellular response to OXPHOS dysfunction. miRNA antagonist transfection improved the energetic state of mutant cybrid cells.","method":"cybrid cell models, miRNA expression analysis, miRNA antagonist transfection, OXPHOS measurements","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — multiple cell models with functional rescue, single lab","pmids":["28740091"],"is_preprint":false},{"year":2018,"finding":"Deletion of mtu1 in zebrafish using CRISPR/Cas9 abolishes 2-thiouridine modification of U34 of mitochondrial tRNALys, tRNAGlu, and tRNAGln, causes global decreases in mitochondrial tRNA levels, impairs mitochondrial translation and respiratory function, reduces ATP production, and results in defects in hearing organs including abnormal otolith size, reduced hair cell numbers, and reduced hair bundle densities.","method":"CRISPR/Cas9 knockout in zebrafish, mass spectrometry of tRNA modifications, Northern blot, mitochondrial translation assay, respiratory complex assays, behavioral tests (startle response, swimming), histology of auditory/vestibular organs","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — in vivo genetic knockout with multiple orthogonal mechanistic and phenotypic readouts","pmids":["30137487"],"is_preprint":false},{"year":2021,"finding":"Mtu1 deficiency in bone marrow mesenchymal stem cells reduces 2-thiouridine modification of mitochondrial tRNAGln, tRNAGlu, and tRNALys, causing respiratory deficiencies and reduced mitochondrial ATP production, which suppresses osteogenic differentiation. Mtu1-deficient mice exhibit osteopenia.","method":"In vitro MSC culture with Mtu1 knockdown, tRNA modification analysis, respiratory chain assays, ATP measurement, osteogenic differentiation assays, mouse knockout model with bone phenotype","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — multiple biochemical readouts in vitro plus in vivo mouse phenotype, single lab","pmids":["33431792"],"is_preprint":false},{"year":2024,"finding":"Pathological missense mutations in MTU1 (TRMU) cause partial loss-of-function and lead to accelerated proteolysis of the mutant protein via direct interaction with the mitochondrial chaperone CLPX, followed by degradation by the mitochondrial caseinolytic peptidase CLPP. Knockdown of CLPP significantly increased mutant MTU1 protein levels and restored mt-tRNA 2-thiolation, demonstrating that accelerated CLPP-mediated proteolysis contributes to disease pathogenesis.","method":"In vitro assays of 17 disease mutations, immunoblotting, CLPP knockdown, co-interaction studies with CLPX, mt-tRNA 2-thiolation measurement, molecular dynamics simulations","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — direct interaction with CLPX/CLPP demonstrated, functional rescue by CLPP knockdown, multiple mutations tested with orthogonal methods","pmids":["38113276"],"is_preprint":false},{"year":2025,"finding":"TRMU expression is elevated in vemurafenib-resistant melanoma cells; genetic depletion of TRMU in resistant cells diminishes oxidative phosphorylation and resensitizes cells to vemurafenib, demonstrating that TRMU-mediated τm5s2U modification of mitochondrial tRNAs supports oxidative phosphorylation and contributes to drug resistance.","method":"Proteomics of epitranscriptomic RWE proteins, TRMU genetic depletion in resistant cell line, OXPHOS measurement, vemurafenib sensitivity assay","journal":"Journal of proteome research","confidence":"Medium","confidence_rationale":"Tier 2-3 / Weak — genetic depletion with functional rescue in single cell line, single lab, single study","pmids":["41213009"],"is_preprint":false},{"year":2026,"finding":"TRMU deficiency causes tissue-specific effects on mitochondrial tRNA conformation, stability, and aminoacylation, with liver being most vulnerable; trmu knockout zebrafish show higher severity of tRNA metabolic failures in liver compared to brain, muscle, eye, and ovum. Liver-specific complex I deficiency was linked to liver-preferential electron flow through complex I, manifesting as hepatic steatosis and enlargement.","method":"trmu knockout zebrafish, mass spectrometry of tRNA modifications across tissues, tRNA conformation/stability/aminoacylation assays per tissue, respiratory complex assembly and activity assays, histopathology","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vivo genetic model with multiple orthogonal biochemical assays across five tissues, single lab","pmids":["41580081"],"is_preprint":false}],"current_model":"TRMU (MTU1) is a mitochondrially-localized tRNA-modifying enzyme that catalyzes 2-thiouridylation of the wobble U34 position in mitochondrial tRNALys, tRNAGlu, and tRNAGln; this modification is required for mitochondrial tRNA stability, efficient aminoacylation, and mitochondrial translation (especially in the liver and hearing organs), and disease-causing mutations lead to accelerated CLPP-mediated proteolysis of the mutant protein, with the degree of residual 2-thiolation correlating with clinical severity."},"narrative":{"mechanistic_narrative":"TRMU (MTU1) is a mitochondrially-localized, mitochondria-specific tRNA-modifying enzyme that catalyzes 2-thiouridylation of the wobble U34 position of mitochondrial tRNALys, tRNAGlu, and tRNAGln [PMID:16513084, PMID:19732863, PMID:21890497]. This modification supports mitochondrial tRNA stability and aminoacylation and is required for efficient mitochondrial translation, as shown by yeast ortholog deletion that destabilizes mitochondrial tRNAs and mRNAs and impairs aminoacylation [PMID:17706197], and by in vivo liver-specific knockout in mouse and CRISPR knockout in zebrafish that abolish 2-thiolation, impair mitochondrial translation and respiratory complex activity, and reduce ATP production [PMID:27689697, PMID:30137487]. The translational requirement is tissue-selective, with the liver being most vulnerable: trmu loss in zebrafish produces the most severe tRNA conformational, stability, and aminoacylation defects in liver, manifesting as complex I deficiency and hepatic steatosis [PMID:41580081]. Loss of TRMU function also elevates reactive oxygen species and triggers apoptosis in hair-cell-like cells [PMID:27405449], and underlies hearing organ defects in zebrafish [PMID:30137487]. Disease-causing missense mutations act as partial loss-of-function alleles: a homozygous A10S variant reduces protein stability and 2-thiouridylation and functions as a nuclear modifier that aggravates the deafness-associated 12S rRNA m.1555A>G mutation [PMID:16826519, PMID:28049726], while a broader set of pathological mutations are subject to accelerated proteolysis through direct interaction with the mitochondrial chaperone CLPX followed by degradation by the CLPP peptidase—CLPP knockdown restores mutant protein levels and tRNA 2-thiolation [PMID:38113276]. TRMU mutations cause acute infantile liver failure with combined respiratory chain deficiency [PMID:19732863].","teleology":[{"year":2006,"claim":"Establishing where TRMU acts and that its loss perturbs the mitochondrial translation apparatus, defining it as a mitochondrial tRNA-modifying enzyme and a disease modifier.","evidence":"GFP-fusion immunofluorescence in mouse and human cells plus genotyping and functional tRNA/protein-synthesis analysis of an A10S modifier of m.1555A>G deafness in patient cells","pmids":["14746906","16513084","16826519"],"confidence":"High","gaps":["Did not define the precise chemical modification catalyzed","Mechanism by which A10S reduces tRNA levels not resolved at the protein-stability level"]},{"year":2009,"claim":"Identifying the enzymatic product and a primary disease phenotype, defining TRMU as the mitochondrial 2-thiouridylase whose deficiency causes infantile liver failure.","evidence":"Homozygosity mapping, mutation identification, and biochemical measurement of 2-thiouridylation in patient tissues","pmids":["19732863"],"confidence":"High","gaps":["Did not establish the in vivo translational consequences of reduced 2-thiolation","Tissue specificity of liver vulnerability not mechanistically explained"]},{"year":2007,"claim":"Resolving whether the modification is required for tRNA integrity, showing that the yeast ortholog is needed for mitochondrial tRNA/mRNA stability and aminoacylation.","evidence":"Northern blots and aminoacylation assays in mto2-null S. cerevisiae","pmids":["17706197"],"confidence":"High","gaps":["Yeast ortholog substrate set may differ from human","Did not address respiratory phenotype severity in vertebrate tissues"]},{"year":2011,"claim":"Testing whether 2-thiolation is strictly required for translation in human cells, finding the function dispensable under normal steady-state tRNA levels with only a Complex II assembly intermediate accumulating.","evidence":"siRNA knockdown, immunoblotting, mitochondrial translation and respiratory chain assays in patient fibroblasts and HEK293 cells","pmids":["21890497"],"confidence":"High","gaps":["Contradicted by in vivo knockout phenotypes, leaving context-dependence unresolved","Did not test conditions of tRNA scarcity or tissue stress"]},{"year":2016,"claim":"Demonstrating in vivo that 2-thiolation is indispensable for mitochondrial translation, resolving the earlier dispensability ambiguity in the liver.","evidence":"Liver-specific Mtu1 knockout mice with mass spectrometry of tRNA modifications, translation and respiratory assays, and electron microscopy","pmids":["27689697"],"confidence":"High","gaps":["Why liver is preferentially affected not mechanistically resolved","Did not address non-hepatic tissues"]},{"year":2016,"claim":"Linking TRMU loss to oxidative stress and cell death in a hearing-relevant cell type, connecting the modification defect to ROS-driven apoptosis.","evidence":"siRNA knockdown in HEI-OC-1 hair-cell-like cells with ROS, mitochondrial function, apoptosis assays, and N-acetylcysteine rescue","pmids":["27405449"],"confidence":"Medium","gaps":["Single cell line, not in vivo","Causal chain from tRNA modification loss to ROS not fully delineated"]},{"year":2017,"claim":"Defining the molecular basis of the A10S modifier allele as a protein-destabilizing mutation in the catalytic domain that lowers 2-thiouridylation.","evidence":"Molecular dynamics, thermal shift, Western blotting, 2-thiouridine and aminoacylation assays, respiration measurements","pmids":["28049726"],"confidence":"High","gaps":["No experimental crystal structure of the enzyme","Mild increase in aminoacylation efficiency unexplained mechanistically"]},{"year":2017,"claim":"Showing TRMU is a regulated node in mitochondrial retrograde signaling, with ROS/Ca2+-induced microRNAs tuning its expression in response to OXPHOS dysfunction.","evidence":"Cybrid models with miRNA expression analysis, antagonist transfection, and OXPHOS measurements","pmids":["28740091"],"confidence":"Medium","gaps":["Specific miRNAs and direct targeting not fully validated","Physiological relevance beyond cybrid models unclear"]},{"year":2018,"claim":"Establishing the vertebrate phenotypic spectrum in vivo, linking 2-thiolation loss to hearing organ defects.","evidence":"CRISPR/Cas9 mtu1 knockout zebrafish with mass spectrometry, Northern blot, translation and respiratory assays, behavioral and histological analysis of auditory/vestibular organs","pmids":["30137487"],"confidence":"High","gaps":["Cell-type basis of hair cell vulnerability not isolated","Did not address tissue-specific severity differences"]},{"year":2021,"claim":"Extending the functional reach of TRMU to skeletal biology, showing its deficiency impairs osteogenic differentiation via mitochondrial energy failure.","evidence":"Mtu1 knockdown in bone marrow MSCs with tRNA modification, respiratory and ATP assays, osteogenic differentiation, and a mouse osteopenia phenotype","pmids":["33431792"],"confidence":"Medium","gaps":["Single lab, partial in vivo characterization","Link between ATP reduction and differentiation block not mechanistically detailed"]},{"year":2024,"claim":"Resolving how missense mutations cause partial loss-of-function, identifying a CLPX-dependent recognition and CLPP-mediated degradation pathway whose inhibition rescues mutant protein and tRNA modification.","evidence":"In vitro analysis of 17 disease mutations, immunoblotting, CLPP knockdown, CLPX co-interaction studies, 2-thiolation measurement, and molecular dynamics","pmids":["38113276"],"confidence":"High","gaps":["Structural basis of CLPX recognition of mutant TRMU unknown","Therapeutic feasibility of CLPP modulation untested in vivo"]},{"year":2025,"claim":"Implicating TRMU in cancer drug resistance, showing its modification activity sustains OXPHOS and vemurafenib resistance in melanoma.","evidence":"Epitranscriptomic proteomics, TRMU genetic depletion in resistant cells, OXPHOS and drug-sensitivity assays","pmids":["41213009"],"confidence":"Medium","gaps":["Single resistant cell line, single study","Mechanism linking modification to resistance metabolism not fully resolved"]},{"year":2026,"claim":"Explaining the longstanding liver-preferential vulnerability by showing tissue-specific failures in tRNA conformation, stability, and aminoacylation, with liver-preferential complex I electron flow driving hepatic complex I deficiency.","evidence":"trmu knockout zebrafish with cross-tissue mass spectrometry, tRNA conformation/stability/aminoacylation assays, respiratory complex assembly/activity assays, and histopathology","pmids":["41580081"],"confidence":"High","gaps":["Molecular determinant of tissue-specific tRNA vulnerability not identified","Whether human tissue specificity follows the same logic untested"]},{"year":null,"claim":"How residual 2-thiolation levels quantitatively dictate clinical severity across tissues, and whether CLPP-pathway or chemical interventions can restore mutant TRMU function therapeutically, remains open.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No high-resolution structure of human TRMU or its substrate complex","Tissue-specific severity determinants not molecularly defined","Therapeutic modulation of CLPP-mediated degradation untested in animals"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140098","term_label":"catalytic activity, acting on RNA","supporting_discovery_ids":[4,5,7,9,11]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[4]},{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[3,5,11]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[0,1,2]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[3,4,5,11]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[7,11]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[2,4,13]}],"complexes":[],"partners":["CLPX","CLPP"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O75648","full_name":"Mitochondrial tRNA-specific 2-thiouridylase 1","aliases":["MTO2 homolog"],"length_aa":421,"mass_kda":47.7,"function":"Catalyzes the 2-thiolation of uridine at the wobble position (U34) of mitochondrial tRNA(Lys), tRNA(Glu) and tRNA(Gln). Required for the formation of 5-taurinomethyl-2-thiouridine (tm5s2U) of mitochondrial tRNA(Lys), tRNA(Glu), and tRNA(Gln) at the wobble position. ATP is required to activate the C2 atom of the wobble base","subcellular_location":"Mitochondrion","url":"https://www.uniprot.org/uniprotkb/O75648/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TRMU","classification":"Not Classified","n_dependent_lines":31,"n_total_lines":1208,"dependency_fraction":0.02566225165562914},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/TRMU","total_profiled":1310},"omim":[{"mim_id":"615438","title":"INFANTILE LIVER FAILURE SYNDROME 1; ILFS1","url":"https://www.omim.org/entry/615438"},{"mim_id":"614667","title":"MITOCHONDRIAL tRNA TRANSLATION OPTIMIZATION 1; MTO1","url":"https://www.omim.org/entry/614667"},{"mim_id":"613070","title":"LIVER FAILURE, INFANTILE, TRANSIENT; LFIT","url":"https://www.omim.org/entry/613070"},{"mim_id":"610957","title":"TYROSYL-tRNA SYNTHETASE 2; YARS2","url":"https://www.omim.org/entry/610957"},{"mim_id":"610230","title":"tRNA 5-METHYLAMINOMETHYL-2-THIOURIDYLATE METHYLTRANSFERASE; TRMU","url":"https://www.omim.org/entry/610230"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Mitochondria","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/TRMU"},"hgnc":{"alias_symbol":["FLJ10140","MTO2","MTU1"],"prev_symbol":["TRMT"]},"alphafold":{"accession":"O75648","domains":[{"cath_id":"3.40.50.620","chopping":"7-143_161-215","consensus_level":"high","plddt":93.2561,"start":7,"end":215},{"cath_id":"2.30.30.280","chopping":"239-296","consensus_level":"high","plddt":95.42,"start":239,"end":296},{"cath_id":"2.40.30.10","chopping":"300-401","consensus_level":"high","plddt":95.8157,"start":300,"end":401}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O75648","model_url":"https://alphafold.ebi.ac.uk/files/AF-O75648-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O75648-F1-predicted_aligned_error_v6.png","plddt_mean":89.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TRMU","jax_strain_url":"https://www.jax.org/strain/search?query=TRMU"},"sequence":{"accession":"O75648","fasta_url":"https://rest.uniprot.org/uniprotkb/O75648.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O75648/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O75648"}},"corpus_meta":[{"pmid":"16826519","id":"PMC_16826519","title":"Mutation in TRMU related to transfer RNA modification modulates the phenotypic expression of the deafness-associated mitochondrial 12S ribosomal RNA mutations.","date":"2006","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/16826519","citation_count":197,"is_preprint":false},{"pmid":"19732863","id":"PMC_19732863","title":"Acute infantile liver failure due to mutations in the TRMU gene.","date":"2009","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/19732863","citation_count":182,"is_preprint":false},{"pmid":"21153446","id":"PMC_21153446","title":"Acute liver failure with subsequent cirrhosis as the primary manifestation of TRMU mutations.","date":"2010","source":"Journal of inherited metabolic disease","url":"https://pubmed.ncbi.nlm.nih.gov/21153446","citation_count":55,"is_preprint":false},{"pmid":"27405449","id":"PMC_27405449","title":"Reduced TRMU expression increases the sensitivity of hair-cell-like HEI-OC-1 cells to neomycin damage in vitro.","date":"2016","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/27405449","citation_count":52,"is_preprint":false},{"pmid":"21890497","id":"PMC_21890497","title":"The 2-thiouridylase function of the human MTU1 (TRMU) enzyme is dispensable for mitochondrial translation.","date":"2011","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/21890497","citation_count":48,"is_preprint":false},{"pmid":"28049726","id":"PMC_28049726","title":"Biochemical Evidence for a Nuclear Modifier Allele (A10S) in TRMU (Methylaminomethyl-2-thiouridylate-methyltransferase) Related to Mitochondrial tRNA Modification in the Phenotypic Manifestation of Deafness-associated 12S rRNA Mutation.","date":"2017","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/28049726","citation_count":47,"is_preprint":false},{"pmid":"27689697","id":"PMC_27689697","title":"Mtu1-Mediated Thiouridine Formation of Mitochondrial tRNAs 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phenotypic expression of the deafness-associated 12S rRNA mutations.","date":"2006","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/16513084","citation_count":30,"is_preprint":false},{"pmid":"33485800","id":"PMC_33485800","title":"TRMU deficiency: A broad clinical spectrum responsive to cysteine supplementation.","date":"2021","source":"Molecular genetics and metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/33485800","citation_count":21,"is_preprint":false},{"pmid":"14746906","id":"PMC_14746906","title":"Identification and characterization of mouse TRMU gene encoding the mitochondrial 5-methylaminomethyl-2-thiouridylate-methyltransferase.","date":"2004","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/14746906","citation_count":20,"is_preprint":false},{"pmid":"35467742","id":"PMC_35467742","title":"Genetic correction of TRMU allele restored the mitochondrial dysfunction-induced deficiencies in iPSCs-derived hair cells of hearing-impaired patients.","date":"2022","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/35467742","citation_count":19,"is_preprint":false},{"pmid":"26243668","id":"PMC_26243668","title":"Mto2 multisite phosphorylation inactivates non-spindle microtubule nucleation complexes during mitosis.","date":"2015","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/26243668","citation_count":19,"is_preprint":false},{"pmid":"17706197","id":"PMC_17706197","title":"Deletion of the MTO2 gene related to tRNA modification causes a failure in mitochondrial RNA metabolism in the yeast Saccharomyces cerevisiae.","date":"2007","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/17706197","citation_count":15,"is_preprint":false},{"pmid":"30740308","id":"PMC_30740308","title":"L-Cysteine supplementation prevents liver transplantation in a patient with TRMU deficiency.","date":"2019","source":"Molecular genetics and metabolism reports","url":"https://pubmed.ncbi.nlm.nih.gov/30740308","citation_count":15,"is_preprint":false},{"pmid":"24339937","id":"PMC_24339937","title":"Nuclear modifier MTO2 modulates the aminoglycoside-sensitivity of mitochondrial 15S rRNA C1477G mutation in Saccharomyces cerevisiae.","date":"2013","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/24339937","citation_count":11,"is_preprint":false},{"pmid":"25665837","id":"PMC_25665837","title":"Hepatic Copper Accumulation: A Novel Feature in Transient Infantile Liver Failure Due to TRMU Mutations?","date":"2015","source":"JIMD reports","url":"https://pubmed.ncbi.nlm.nih.gov/25665837","citation_count":10,"is_preprint":false},{"pmid":"38113276","id":"PMC_38113276","title":"Pathological mutations promote proteolysis of mitochondrial tRNA-specific 2-thiouridylase 1 (MTU1) via mitochondrial caseinolytic peptidase (CLPP).","date":"2024","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/38113276","citation_count":9,"is_preprint":false},{"pmid":"28740091","id":"PMC_28740091","title":"microRNA-mediated differential expression of TRMU, GTPBP3 and MTO1 in cell models of mitochondrial-DNA diseases.","date":"2017","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/28740091","citation_count":9,"is_preprint":false},{"pmid":"33431792","id":"PMC_33431792","title":"Mtu1 defects are correlated with reduced osteogenic differentiation.","date":"2021","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/33431792","citation_count":9,"is_preprint":false},{"pmid":"33365252","id":"PMC_33365252","title":"Leigh syndrome associated with TRMU gene mutations.","date":"2020","source":"Molecular genetics and metabolism reports","url":"https://pubmed.ncbi.nlm.nih.gov/33365252","citation_count":8,"is_preprint":false},{"pmid":"32520628","id":"PMC_32520628","title":"Microtubule nucleation promoters Mto1 and Mto2 regulate cytokinesis in fission yeast.","date":"2020","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/32520628","citation_count":7,"is_preprint":false},{"pmid":"29374875","id":"PMC_29374875","title":"[TRMU MUTATIONS - REVERSIBLE INFANTILE LIVER FAILURE OR MULTISYSTEM DISORDER?].","date":"2018","source":"Harefuah","url":"https://pubmed.ncbi.nlm.nih.gov/29374875","citation_count":6,"is_preprint":false},{"pmid":"41580081","id":"PMC_41580081","title":"Deficient mitochondrial tRNA modifications arising from TRMU mutation led to the liver-specific failure.","date":"2026","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/41580081","citation_count":0,"is_preprint":false},{"pmid":"41213009","id":"PMC_41213009","title":"TRMU Confers Resistance of Melanoma Cells to Vemurafenib through Modulating Mitochondrial Activities.","date":"2025","source":"Journal of proteome research","url":"https://pubmed.ncbi.nlm.nih.gov/41213009","citation_count":0,"is_preprint":false},{"pmid":"41989917","id":"PMC_41989917","title":"The endoplasmic reticulum protein Erg28 restrains Mto1-Mto2-γ-TuSC-mediated microtubule assembly.","date":"2026","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/41989917","citation_count":0,"is_preprint":false},{"pmid":"35867014","id":"PMC_35867014","title":"Perioperative Management of Liver Retransplant in an Adult With a History of TRMU Alteration.","date":"2022","source":"Experimental and clinical transplantation : official journal of the Middle East Society for Organ Transplantation","url":"https://pubmed.ncbi.nlm.nih.gov/35867014","citation_count":0,"is_preprint":false},{"pmid":"41939582","id":"PMC_41939582","title":"Fatal Infantile Hepatic Dysfunction Associated With TRMU Gene Mutation and Aggravated by Cytomegalovirus Infection: A Unique Case.","date":"2026","source":"Cureus","url":"https://pubmed.ncbi.nlm.nih.gov/41939582","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":15090,"output_tokens":4121,"usd":0.053542,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12214,"output_tokens":4186,"usd":0.08286,"stage2_stop_reason":"end_turn"},"total_usd":0.136402,"stage1_batch_id":"msgbatch_017qqVz33Ga63SCDwzb35XPb","stage2_batch_id":"msgbatch_01Scr2Ei9x4HJMiRGxwrmvLK","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2004,\n      \"finding\": \"Mouse TRMU protein localizes to mitochondria, as demonstrated by immunofluorescence of NIH3T3 cells expressing TRMU-GFP fusion protein, establishing it as a mitochondrial tRNA-modifying enzyme homologous to bacterial TrmU.\",\n      \"method\": \"Immunofluorescence microscopy of TRMU-GFP fusion protein in NIH3T3 cells\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct localization experiment with GFP fusion, replicated in human cells (PMID:16513084), single lab\",\n      \"pmids\": [\"14746906\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Human TRMU protein localizes to mitochondria, demonstrated by immunofluorescence of human 143B cells expressing TRMU-GFP fusion protein.\",\n      \"method\": \"Immunofluorescence microscopy of TRMU-GFP fusion protein in human 143B cells\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct localization experiment, consistent with mouse data (PMID:14746906), single lab\",\n      \"pmids\": [\"16513084\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"A homozygous missense mutation (A10S) in TRMU reduces steady-state levels of mitochondrial tRNAs and impairs mitochondrial protein synthesis, acting as a nuclear modifier that aggravates mitochondrial dysfunction associated with the 12S rRNA A1555G mutation to cause deafness. The A10S mutation does not affect mitochondrial import of TRMU.\",\n      \"method\": \"Genotyping, functional analysis of mitochondrial tRNA levels and protein synthesis in patient-derived cells, import assay\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal biochemical methods (tRNA quantification, protein synthesis, import assay) in patient cells, replicated and extended by subsequent studies\",\n      \"pmids\": [\"16826519\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"In yeast S. cerevisiae, deletion of MTO2 (the yeast ortholog of TRMU) causes marked decreases in steady-state levels of mitochondrial tRNAs (tRNALys, tRNAGlu, tRNAGln, tRNALeu, tRNAGly, tRNAMet), impairs aminoacylation of tRNALys and tRNALeu, and reduces steady-state levels of mitochondrial mRNAs (CYTB, COX1, COX2, COX3, ATP6), demonstrating that tRNA modification by MTO2 is required for mitochondrial RNA stability.\",\n      \"method\": \"Northern blot analysis of mitochondrial tRNA and mRNA levels; aminoacylation assays in mto2 null yeast strains\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro assays (aminoacylation) plus multiple RNA quantification methods in genetic knockout, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"17706197\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"TRMU encodes a mitochondria-specific tRNA-modifying enzyme (tRNA 5-methylaminomethyl-2-thiouridylate methyltransferase) responsible for 2-thiouridylation of mitochondrial tRNAs; mutations in TRMU cause markedly reduced 2-thiouridylation levels of mitochondrial tRNAs and result in acute infantile liver failure with combined respiratory chain deficiency without mtDNA depletion.\",\n      \"method\": \"Homozygosity mapping, mutation identification, biochemical measurement of 2-thiouridylation levels in patient tissues\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct biochemical measurement of enzymatic product (2-thiouridylation) in patient cells, 13 unrelated patients, replicated across multiple studies\",\n      \"pmids\": [\"19732863\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Loss of MTU1 (TRMU) in patient fibroblasts and HEK293 cells severely reduces 2-thiolation of mitochondrial tRNALys, tRNAGlu, and tRNAGln but does not impair overall mitochondrial translation at normal steady-state tRNA levels, indicating the 2-thiouridylase function is dispensable for translation under these conditions. The only respiratory chain abnormality observed was accumulation of a Complex II assembly intermediate without affecting fully assembled enzyme levels.\",\n      \"method\": \"Immunoblotting, siRNA knockdown, analysis of mitochondrial translation, respiratory chain enzyme assays in patient fibroblasts and HEK293 cells\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (immunoblot, siRNA KD, translation assay, respiratory chain assay) in two cell systems, single lab; contradicts some prior assumptions\",\n      \"pmids\": [\"21890497\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"In yeast, deletion of the nuclear modifier gene MTO2 suppresses aminoglycoside-sensitivity of mitochondrial 15S rRNA C1477G mutation; the double mutant (mto2/C1477G) shows decreased oxygen consumption but compensates through upregulation of glycolytic genes (HXK2, PFK1, PYK1), providing energy via glycolysis.\",\n      \"method\": \"Genetic epistasis analysis, oxygen consumption measurements, gene expression analysis, glycolytic inhibitor treatment in S. cerevisiae\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with multiple functional readouts, single lab\",\n      \"pmids\": [\"24339937\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Liver-specific knockout of Mtu1 in mice causes loss of 2-thiolation in mitochondrial tRNAs, leading to marked impairment of mitochondrial translation, disruption of mitochondrial membrane integrity, and broad decrease in respiratory complex activities in hepatocytes, demonstrating that Mtu1-dependent 2-thiolation of mt-tRNA is indispensable for mitochondrial translation in vivo.\",\n      \"method\": \"Liver-specific Mtu1 knockout mouse model, mass spectrometry of tRNA modifications, mitochondrial translation assay, respiratory complex activity assays, electron microscopy\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — genetic knockout in vivo with multiple orthogonal mechanistic readouts; directly demonstrates requirement for translation in vivo\",\n      \"pmids\": [\"27689697\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Reduced TRMU expression in HEI-OC-1 hair-cell-like cells increases mitochondrial dysfunction and reactive oxygen species (ROS) levels after neomycin treatment, leading to increased apoptosis; N-acetylcysteine rescued the mitochondrial dysfunction and apoptosis, indicating TRMU regulates mitochondrial function and ROS levels in this context.\",\n      \"method\": \"siRNA knockdown of TRMU in HEI-OC-1 cells, ROS measurement, mitochondrial function assays, cell viability/apoptosis assays, N-acetylcysteine rescue experiment\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — siRNA KD with multiple functional readouts and chemical rescue, single lab\",\n      \"pmids\": [\"27405449\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The TRMU A10S mutation introduces a Ser10 dynamic electrostatic interaction with Lys106 in the catalytic domain (shown by molecular dynamics simulations), reduces TRMU protein levels, reduces thermal stability of the TRMU protein, and causes marked decreases in 2-thiouridine modification of U34 of tRNALys, tRNAGlu, and tRNAGln while mildly increasing aminoacylation efficiency of tRNAs. The defective 2-thiouridine modification worsens mitochondrial translation impairment associated with m.1555A>G mutation, reducing respiratory chain activities, ATP production, and elevating ROS.\",\n      \"method\": \"Molecular dynamics simulation, Western blotting, thermal shift assay, tRNA modification analysis (2-thiouridine levels), aminoacylation assays, mitochondrial translation and respiration measurements\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — multiple orthogonal biochemical and structural methods including in vitro enzymatic assays and mutagenesis analysis, single lab\",\n      \"pmids\": [\"28049726\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Expression of TRMU is regulated by microRNAs induced by retrograde mitochondrial signals (ROS and Ca2+) in cybrid models of mtDNA diseases, altering the modification status of mitochondrial tRNAs as part of a cellular response to OXPHOS dysfunction. miRNA antagonist transfection improved the energetic state of mutant cybrid cells.\",\n      \"method\": \"cybrid cell models, miRNA expression analysis, miRNA antagonist transfection, OXPHOS measurements\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — multiple cell models with functional rescue, single lab\",\n      \"pmids\": [\"28740091\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Deletion of mtu1 in zebrafish using CRISPR/Cas9 abolishes 2-thiouridine modification of U34 of mitochondrial tRNALys, tRNAGlu, and tRNAGln, causes global decreases in mitochondrial tRNA levels, impairs mitochondrial translation and respiratory function, reduces ATP production, and results in defects in hearing organs including abnormal otolith size, reduced hair cell numbers, and reduced hair bundle densities.\",\n      \"method\": \"CRISPR/Cas9 knockout in zebrafish, mass spectrometry of tRNA modifications, Northern blot, mitochondrial translation assay, respiratory complex assays, behavioral tests (startle response, swimming), histology of auditory/vestibular organs\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — in vivo genetic knockout with multiple orthogonal mechanistic and phenotypic readouts\",\n      \"pmids\": [\"30137487\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Mtu1 deficiency in bone marrow mesenchymal stem cells reduces 2-thiouridine modification of mitochondrial tRNAGln, tRNAGlu, and tRNALys, causing respiratory deficiencies and reduced mitochondrial ATP production, which suppresses osteogenic differentiation. Mtu1-deficient mice exhibit osteopenia.\",\n      \"method\": \"In vitro MSC culture with Mtu1 knockdown, tRNA modification analysis, respiratory chain assays, ATP measurement, osteogenic differentiation assays, mouse knockout model with bone phenotype\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — multiple biochemical readouts in vitro plus in vivo mouse phenotype, single lab\",\n      \"pmids\": [\"33431792\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Pathological missense mutations in MTU1 (TRMU) cause partial loss-of-function and lead to accelerated proteolysis of the mutant protein via direct interaction with the mitochondrial chaperone CLPX, followed by degradation by the mitochondrial caseinolytic peptidase CLPP. Knockdown of CLPP significantly increased mutant MTU1 protein levels and restored mt-tRNA 2-thiolation, demonstrating that accelerated CLPP-mediated proteolysis contributes to disease pathogenesis.\",\n      \"method\": \"In vitro assays of 17 disease mutations, immunoblotting, CLPP knockdown, co-interaction studies with CLPX, mt-tRNA 2-thiolation measurement, molecular dynamics simulations\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — direct interaction with CLPX/CLPP demonstrated, functional rescue by CLPP knockdown, multiple mutations tested with orthogonal methods\",\n      \"pmids\": [\"38113276\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"TRMU expression is elevated in vemurafenib-resistant melanoma cells; genetic depletion of TRMU in resistant cells diminishes oxidative phosphorylation and resensitizes cells to vemurafenib, demonstrating that TRMU-mediated τm5s2U modification of mitochondrial tRNAs supports oxidative phosphorylation and contributes to drug resistance.\",\n      \"method\": \"Proteomics of epitranscriptomic RWE proteins, TRMU genetic depletion in resistant cell line, OXPHOS measurement, vemurafenib sensitivity assay\",\n      \"journal\": \"Journal of proteome research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Weak — genetic depletion with functional rescue in single cell line, single lab, single study\",\n      \"pmids\": [\"41213009\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"TRMU deficiency causes tissue-specific effects on mitochondrial tRNA conformation, stability, and aminoacylation, with liver being most vulnerable; trmu knockout zebrafish show higher severity of tRNA metabolic failures in liver compared to brain, muscle, eye, and ovum. Liver-specific complex I deficiency was linked to liver-preferential electron flow through complex I, manifesting as hepatic steatosis and enlargement.\",\n      \"method\": \"trmu knockout zebrafish, mass spectrometry of tRNA modifications across tissues, tRNA conformation/stability/aminoacylation assays per tissue, respiratory complex assembly and activity assays, histopathology\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vivo genetic model with multiple orthogonal biochemical assays across five tissues, single lab\",\n      \"pmids\": [\"41580081\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TRMU (MTU1) is a mitochondrially-localized tRNA-modifying enzyme that catalyzes 2-thiouridylation of the wobble U34 position in mitochondrial tRNALys, tRNAGlu, and tRNAGln; this modification is required for mitochondrial tRNA stability, efficient aminoacylation, and mitochondrial translation (especially in the liver and hearing organs), and disease-causing mutations lead to accelerated CLPP-mediated proteolysis of the mutant protein, with the degree of residual 2-thiolation correlating with clinical severity.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TRMU (MTU1) is a mitochondrially-localized, mitochondria-specific tRNA-modifying enzyme that catalyzes 2-thiouridylation of the wobble U34 position of mitochondrial tRNALys, tRNAGlu, and tRNAGln [#1, #4, #5]. This modification supports mitochondrial tRNA stability and aminoacylation and is required for efficient mitochondrial translation, as shown by yeast ortholog deletion that destabilizes mitochondrial tRNAs and mRNAs and impairs aminoacylation [#3], and by in vivo liver-specific knockout in mouse and CRISPR knockout in zebrafish that abolish 2-thiolation, impair mitochondrial translation and respiratory complex activity, and reduce ATP production [#7, #11]. The translational requirement is tissue-selective, with the liver being most vulnerable: trmu loss in zebrafish produces the most severe tRNA conformational, stability, and aminoacylation defects in liver, manifesting as complex I deficiency and hepatic steatosis [#15]. Loss of TRMU function also elevates reactive oxygen species and triggers apoptosis in hair-cell-like cells [#8], and underlies hearing organ defects in zebrafish [#11]. Disease-causing missense mutations act as partial loss-of-function alleles: a homozygous A10S variant reduces protein stability and 2-thiouridylation and functions as a nuclear modifier that aggravates the deafness-associated 12S rRNA m.1555A>G mutation [#2, #9], while a broader set of pathological mutations are subject to accelerated proteolysis through direct interaction with the mitochondrial chaperone CLPX followed by degradation by the CLPP peptidase—CLPP knockdown restores mutant protein levels and tRNA 2-thiolation [#13]. TRMU mutations cause acute infantile liver failure with combined respiratory chain deficiency [#4].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Establishing where TRMU acts and that its loss perturbs the mitochondrial translation apparatus, defining it as a mitochondrial tRNA-modifying enzyme and a disease modifier.\",\n      \"evidence\": \"GFP-fusion immunofluorescence in mouse and human cells plus genotyping and functional tRNA/protein-synthesis analysis of an A10S modifier of m.1555A>G deafness in patient cells\",\n      \"pmids\": [\"14746906\", \"16513084\", \"16826519\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the precise chemical modification catalyzed\", \"Mechanism by which A10S reduces tRNA levels not resolved at the protein-stability level\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identifying the enzymatic product and a primary disease phenotype, defining TRMU as the mitochondrial 2-thiouridylase whose deficiency causes infantile liver failure.\",\n      \"evidence\": \"Homozygosity mapping, mutation identification, and biochemical measurement of 2-thiouridylation in patient tissues\",\n      \"pmids\": [\"19732863\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish the in vivo translational consequences of reduced 2-thiolation\", \"Tissue specificity of liver vulnerability not mechanistically explained\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Resolving whether the modification is required for tRNA integrity, showing that the yeast ortholog is needed for mitochondrial tRNA/mRNA stability and aminoacylation.\",\n      \"evidence\": \"Northern blots and aminoacylation assays in mto2-null S. cerevisiae\",\n      \"pmids\": [\"17706197\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Yeast ortholog substrate set may differ from human\", \"Did not address respiratory phenotype severity in vertebrate tissues\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Testing whether 2-thiolation is strictly required for translation in human cells, finding the function dispensable under normal steady-state tRNA levels with only a Complex II assembly intermediate accumulating.\",\n      \"evidence\": \"siRNA knockdown, immunoblotting, mitochondrial translation and respiratory chain assays in patient fibroblasts and HEK293 cells\",\n      \"pmids\": [\"21890497\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Contradicted by in vivo knockout phenotypes, leaving context-dependence unresolved\", \"Did not test conditions of tRNA scarcity or tissue stress\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Demonstrating in vivo that 2-thiolation is indispensable for mitochondrial translation, resolving the earlier dispensability ambiguity in the liver.\",\n      \"evidence\": \"Liver-specific Mtu1 knockout mice with mass spectrometry of tRNA modifications, translation and respiratory assays, and electron microscopy\",\n      \"pmids\": [\"27689697\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why liver is preferentially affected not mechanistically resolved\", \"Did not address non-hepatic tissues\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Linking TRMU loss to oxidative stress and cell death in a hearing-relevant cell type, connecting the modification defect to ROS-driven apoptosis.\",\n      \"evidence\": \"siRNA knockdown in HEI-OC-1 hair-cell-like cells with ROS, mitochondrial function, apoptosis assays, and N-acetylcysteine rescue\",\n      \"pmids\": [\"27405449\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single cell line, not in vivo\", \"Causal chain from tRNA modification loss to ROS not fully delineated\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Defining the molecular basis of the A10S modifier allele as a protein-destabilizing mutation in the catalytic domain that lowers 2-thiouridylation.\",\n      \"evidence\": \"Molecular dynamics, thermal shift, Western blotting, 2-thiouridine and aminoacylation assays, respiration measurements\",\n      \"pmids\": [\"28049726\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No experimental crystal structure of the enzyme\", \"Mild increase in aminoacylation efficiency unexplained mechanistically\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Showing TRMU is a regulated node in mitochondrial retrograde signaling, with ROS/Ca2+-induced microRNAs tuning its expression in response to OXPHOS dysfunction.\",\n      \"evidence\": \"Cybrid models with miRNA expression analysis, antagonist transfection, and OXPHOS measurements\",\n      \"pmids\": [\"28740091\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific miRNAs and direct targeting not fully validated\", \"Physiological relevance beyond cybrid models unclear\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Establishing the vertebrate phenotypic spectrum in vivo, linking 2-thiolation loss to hearing organ defects.\",\n      \"evidence\": \"CRISPR/Cas9 mtu1 knockout zebrafish with mass spectrometry, Northern blot, translation and respiratory assays, behavioral and histological analysis of auditory/vestibular organs\",\n      \"pmids\": [\"30137487\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cell-type basis of hair cell vulnerability not isolated\", \"Did not address tissue-specific severity differences\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Extending the functional reach of TRMU to skeletal biology, showing its deficiency impairs osteogenic differentiation via mitochondrial energy failure.\",\n      \"evidence\": \"Mtu1 knockdown in bone marrow MSCs with tRNA modification, respiratory and ATP assays, osteogenic differentiation, and a mouse osteopenia phenotype\",\n      \"pmids\": [\"33431792\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab, partial in vivo characterization\", \"Link between ATP reduction and differentiation block not mechanistically detailed\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Resolving how missense mutations cause partial loss-of-function, identifying a CLPX-dependent recognition and CLPP-mediated degradation pathway whose inhibition rescues mutant protein and tRNA modification.\",\n      \"evidence\": \"In vitro analysis of 17 disease mutations, immunoblotting, CLPP knockdown, CLPX co-interaction studies, 2-thiolation measurement, and molecular dynamics\",\n      \"pmids\": [\"38113276\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of CLPX recognition of mutant TRMU unknown\", \"Therapeutic feasibility of CLPP modulation untested in vivo\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Implicating TRMU in cancer drug resistance, showing its modification activity sustains OXPHOS and vemurafenib resistance in melanoma.\",\n      \"evidence\": \"Epitranscriptomic proteomics, TRMU genetic depletion in resistant cells, OXPHOS and drug-sensitivity assays\",\n      \"pmids\": [\"41213009\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single resistant cell line, single study\", \"Mechanism linking modification to resistance metabolism not fully resolved\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Explaining the longstanding liver-preferential vulnerability by showing tissue-specific failures in tRNA conformation, stability, and aminoacylation, with liver-preferential complex I electron flow driving hepatic complex I deficiency.\",\n      \"evidence\": \"trmu knockout zebrafish with cross-tissue mass spectrometry, tRNA conformation/stability/aminoacylation assays, respiratory complex assembly/activity assays, and histopathology\",\n      \"pmids\": [\"41580081\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular determinant of tissue-specific tRNA vulnerability not identified\", \"Whether human tissue specificity follows the same logic untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How residual 2-thiolation levels quantitatively dictate clinical severity across tissues, and whether CLPP-pathway or chemical interventions can restore mutant TRMU function therapeutically, remains open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No high-resolution structure of human TRMU or its substrate complex\", \"Tissue-specific severity determinants not molecularly defined\", \"Therapeutic modulation of CLPP-mediated degradation untested in animals\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140098\", \"supporting_discovery_ids\": [4, 5, 7, 9, 11]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [3, 5, 11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0, 1, 2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [3, 4, 5, 11]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [7, 11]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [2, 4, 13]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"CLPX\", \"CLPP\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}