{"gene":"NEMF","run_date":"2026-04-29T11:37:56","timeline":{"discoveries":[{"year":2015,"finding":"NEMF is required for Listerin's specificity toward nascent chain-containing 60S subunits. Cryo-EM structure at 3.6 Å of the nascent chain-60S-Listerin-NEMF complex showed that NEMF makes simultaneous contacts with the 60S ribosomal subunit and peptidyl-tRNA to sense nascent chain occupancy, while ribosome-bound NEMF recruits and stabilizes Listerin's N-terminal domain; Listerin's C-terminal RWD domain directly contacts the ribosome to position its ligase domain near the nascent polypeptide exit tunnel.","method":"Cryo-EM structure determination (3.6 Å), structural and mutational analyses, in vitro reconstitution","journal":"Molecular Cell","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM structure plus mutagenesis in a single rigorous study","pmids":["25578875"],"is_preprint":false},{"year":2016,"finding":"Rqc2/Tae2 (NEMF ortholog in yeast) modifies ribosome-stalled nascent polypeptide chains with C-terminal Ala- and Thr-containing extensions ('CAT tails'), and CATylation mediates formation of detergent-insoluble protein aggregates; inefficient ubiquitination by Ltn1 (Listerin) favors this Rqc2-mediated aggregation reaction.","method":"Genetic epistasis (Ltn1 inactivation), biochemical fractionation (detergent-insolubility assay), in vivo labeling of nascent chains in yeast","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal genetic and biochemical methods; highly cited foundational study","pmids":["26943317"],"is_preprint":false},{"year":2019,"finding":"ANKZF1 (yeast Vms1p) releases ubiquitinated nascent proteins from 60S ribosomal subunits during RQC; NEMF-mediated CAT tailing functions upstream of this release step. Cell-free reconstitution showed ANKZF1/Vms1p cleave polypeptidyl-tRNAs at the 3'CCA terminus on RQC complexes, and tRNA recycling requires TRNT1.","method":"Cell-free reconstitution system, biochemical cleavage assays","journal":"Nature Structural & Molecular Biology","confidence":"Medium","confidence_rationale":"Tier 1 in vitro reconstitution but NEMF's role is contextual/upstream rather than directly assayed","pmids":["31011209"],"is_preprint":false},{"year":2020,"finding":"Three independently generated mouse models with mutations in NEMF/Rqc2 develop progressive motor neuron degeneration; equivalent mutations in yeast Rqc2 selectively interfere with C-terminal tail modification of aberrant translation products, implicating defective RQC-mediated protein degradation as the pathomechanism. Human NEMF mutations from seven families presenting juvenile neuromuscular disease were identified.","method":"Mouse genetic models (three independent lines), yeast genetics, human exome sequencing","journal":"Nature Communications","confidence":"High","confidence_rationale":"Tier 2 — three independent mouse models plus yeast functional validation replicated across multiple families","pmids":["32934225"],"is_preprint":false},{"year":2020,"finding":"Knockdown of Nemf in cultured mouse primary cortical neurons impairs axonal outgrowth and synapse development, demonstrating NEMF is required for mammalian neuron development.","method":"siRNA knockdown in primary cortical neurons, immunofluorescence imaging of axonal morphology and synaptic markers","journal":"Human Genetics","confidence":"Medium","confidence_rationale":"Tier 2/3 — KD with defined cellular phenotype in primary neurons, single study","pmids":["33048237"],"is_preprint":false},{"year":2021,"finding":"Mammalian NEMF has a Listerin-independent proteolytic role mediated by tRNA-Ala binding and alanine tailing; Ala tails signal proteolysis indirectly through the C-end rule pathway, with CRL2KLHDC10 E3 ligase complex and Pirh2/Rchy1 identified as E3 ligases that directly bind Ala-tailed ribosome stalling products and target them for degradation.","method":"Biochemical pulldowns, co-immunoprecipitation, in vitro ubiquitination assays, mutational analysis of NEMF tRNA-Ala binding domain, cell-based degradation assays","journal":"Molecular Cell","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal biochemical methods including in vitro ubiquitination reconstitution and mutagenesis","pmids":["33909987"],"is_preprint":false},{"year":2021,"finding":"The nascent polypeptide sequence in the 60S ribosomal exit tunnel determines Rqc2 (NEMF ortholog) dependency for RQC; polytryptophan sequences (≥11 residues) induce Rqc2-independent RQC not coupled with CAT tailing, while eight consecutive tryptophan residues proximal to the peptidyl transferase center inhibit CAT tailing triggered by tandem CGA codons.","method":"Yeast genetics, in vivo reporter assays for CAT tailing and ubiquitination, mutant analysis","journal":"Nucleic Acids Research","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis with multiple reporters but single lab","pmids":["33511411"],"is_preprint":false},{"year":2022,"finding":"NEMF and its orthologs (yeast Rqc2, bacterial RqcH) are central RQC players that sense large ribosomal subunits obstructed with nascent chains, promote nascent-chain proteolysis by stabilizing LTN1/Listerin binding, and mediate C-terminal untemplated polypeptide elongation (CAT/Ala tailing) to expose ribosome-buried lysines for ubiquitination; C-terminal tails also function as extra-ribosomal degrons across evolution.","method":"Review synthesizing structural, biochemical, and genetic data from multiple studies","journal":"Molecular Cell","confidence":"Medium","confidence_rationale":"Tier 2 — synthesis of multiple orthogonal studies, but review article","pmids":["35452614"],"is_preprint":false},{"year":2024,"finding":"NEMF mediates a Listerin-independent, organelle-specific mitochondrial RQC pathway: mitochondrial nascent polypeptides stalled at the ribosome receive NEMF-mediated C-terminal poly-alanine modifications, which are then recognized by cytosolic E3 ligase Pirh2 and the mitochondrial ClpXP protease to coordinately clear the stalled chains; defects in this pathway cause NEMF-mediated protein aggregates and mitochondrial integrity failure.","method":"Co-immunoprecipitation, biochemical fractionation, in vivo reporter assays for mitochondrial RQC, NEMF mutant analysis, protease activity assays","journal":"Cell Reports","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods identifying a novel organelle-specific pathway with functional validation","pmids":["38412092"],"is_preprint":false},{"year":2024,"finding":"A tandem MS/MS protocol using customized spectral database searching was developed to identify NEMF-mediated C-terminal extended sequences (CESs) on ribosome-stalled mitochondrial nascent chains, demonstrating that NEMF appends compositionally diverse C-terminal extensions beyond canonical poly-alanine.","method":"Tandem mass spectrometry (MS/MS) with customized spectral database, sample preparation from mitochondrial fractions","journal":"STAR Protocols","confidence":"Medium","confidence_rationale":"Tier 2 — direct biochemical identification of NEMF-modified peptides by MS, methodological/protocol paper","pmids":["39395174"],"is_preprint":false},{"year":2024,"finding":"NEMF mutant mouse models (NemfR86S and NemfR487G) display an Importin-β-specific nuclear import block, cytoplasmic mislocalization and aggregation of TDP43, Importin-β, RanGAP1, and Ran, and a pathological physical interaction between Importin-β and mutant NEMFR86S protein in cytoplasmic accumulations, suggesting that NEMF mutations cause neurodegeneration partly through disruption of nucleocytoplasmic transport.","method":"Mouse genetic models, co-immunoprecipitation, immunofluorescence localization, pharmacological inhibition of Importin-β in mouse and human cells","journal":"PLoS Genetics","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP and localization with functional consequence in two mouse models plus human cells","pmids":["39312574"],"is_preprint":false},{"year":2024,"finding":"TCF25 (Rqc1 in yeast) interacts with the RING domain of Listerin and the acceptor ubiquitin to impose K48 linkage specificity on Listerin-mediated ubiquitination of nascent chains on 60S RNCs that associate with NEMF; NEMF promotes 60S RNC association with Listerin upstream of this TCF25-dependent step.","method":"Biochemical ubiquitination assays, co-immunoprecipitation, AlphaFold3 modeling","journal":"bioRxiv (preprint)","confidence":"Medium","confidence_rationale":"Tier 1–2 — functional biochemical reconstitution with structural modeling, but preprint only","pmids":["bio_10.1101_2024.10.17.618946"],"is_preprint":true},{"year":2024,"finding":"Selective impairment of NEMF's Ala-tailing activity in mice (homozygous Nemf mutation) causes mild motor defects but synthetic lethality when combined with the lister (Listerin) neurodegeneration mutation; conversely, partial reduction of Ala-tailing capacity (heterozygous Nemf mutation) markedly improves the lister phenotype. RQC substrates that evade degradation form amyloid-like aggregates in an Ala-tail-dependent fashion.","method":"Mouse genetic models, genetic epistasis (double mutant analysis), biochemical aggregation assays (amyloid-like aggregate characterization)","journal":"bioRxiv (preprint)","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis with multiple mouse models and biochemical aggregate characterization, but preprint","pmids":["bio_10.1101_2024.08.24.608776"],"is_preprint":true},{"year":2025,"finding":"NEMF-mediated CAT tailing is required for translocation-associated quality control (TAQC) of nonstop (NS) mRNA-encoded nascent chains stalled during co-translational translocation at the ER. An AT-rich CAT tail functions as a degron directing substrates through an unconventional ERAD mechanism involving ER-to-Golgi trafficking and KDEL-mediated retrieval at the Golgi, while an AG-rich tail directs secretory proteins to the lysosome.","method":"Genome-wide CRISPR screen, live-cell imaging, biochemical degradation assays, CAT-tail mimetic characterization","journal":"Journal of Cell Biology","confidence":"High","confidence_rationale":"Tier 1–2 — genome-wide CRISPR screen combined with live imaging and multiple biochemical assays in peer-reviewed publication","pmids":["40257401"],"is_preprint":false},{"year":2025,"finding":"A cryo-EM structure of the yeast RQC complex revealed how the F340I mutation in Rqc2 (NEMF ortholog) alters its binding to the 60S subunit, disrupting the A-site's ability to bind tRNA in the presence of Ltn1 and thereby limiting CAT tailing; a genetic screen identified this Rqc2 mutant allele as involved in peptide release from stalled ribosomes.","method":"Cryo-EM structure determination, genetic screen, functional assays for peptide release and CAT tailing","journal":"Structure","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM structure with mutagenesis and functional genetic validation","pmids":["40187343"],"is_preprint":false},{"year":2025,"finding":"Canonical RQC factors including NEMF and LTN1 associate with ribosomes stalled at the ER; ribosome splitting is a prerequisite for UFMylation of RPL26 on ER-stalled ribosomes, but UFMylation persists without late RQC components NEMF and LTN1, indicating UFMylation acts in concert with but independently downstream of early RQC steps to clear arrested polypeptides.","method":"Functional cellular assays with ER-targeted stalling reporters, co-immunoprecipitation, genetic epistasis (knockout of RQC factors)","journal":"bioRxiv (preprint)","confidence":"Medium","confidence_rationale":"Tier 2 — epistasis and co-IP with defined reporters, but preprint","pmids":["bio_10.1101_2025.01.17.633636"],"is_preprint":true}],"current_model":"NEMF (nuclear export mediator factor) is the central scaffolding and tRNA-binding component of the eukaryotic ribosome-associated quality control (RQC) complex: it binds obstructed 60S ribosomal subunits by sensing both the ribosome surface and peptidyl-tRNA, recruits and stabilizes the E3 ubiquitin ligase Listerin for nascent-chain ubiquitylation, and independently appends C-terminal poly-alanine (and mixed Ala/Thr) tails to stalled nascent chains via tRNA-Ala binding; these CAT tails expose ribosome-buried lysines for Listerin-dependent ubiquitylation, serve as direct degrons recognized by alternative E3 ligases (CRL2KLHDC10, Pirh2) in a Listerin-independent C-end rule pathway, direct stalled mitochondrial nascent chains to ClpXP-mediated degradation, sort ER-translocon-clogging nonstop substrates through a Golgi-retrieval ERAD route, and—when degradation fails—drive amyloid-like protein aggregation; mutations in NEMF that impair these functions cause progressive motor neuron degeneration in mice and juvenile neuromuscular disease in humans."},"narrative":{"teleology":[{"year":2015,"claim":"Establishing how NEMF senses ribosome-stalled nascent chains and recruits Listerin resolved the fundamental question of how the RQC complex achieves substrate specificity on 60S subunits.","evidence":"Cryo-EM structure at 3.6 Å of the 60S–NEMF–Listerin complex with mutagenesis and in vitro reconstitution","pmids":["25578875"],"confidence":"High","gaps":["Structural basis for tRNA binding by NEMF not resolved in this complex","Mechanism of CAT tailing not yet discovered"]},{"year":2016,"claim":"Discovery that the NEMF ortholog Rqc2 appends untemplated C-terminal Ala/Thr tails to stalled nascent chains revealed a second, Listerin-independent function and linked failed degradation to toxic protein aggregation.","evidence":"Genetic epistasis with Ltn1, detergent-insolubility assays, and in vivo nascent chain labeling in yeast","pmids":["26943317"],"confidence":"High","gaps":["Mammalian CAT tailing not yet demonstrated","E3 ligases recognizing CAT tails as degrons not identified"]},{"year":2020,"claim":"Three independent NEMF-mutant mouse lines developing progressive motor neuron degeneration, together with human family studies, established NEMF as a disease gene and linked impaired CAT tailing to neurodegeneration.","evidence":"Three mouse genetic models, yeast functional validation of orthologous mutations, and exome sequencing of seven human families","pmids":["32934225"],"confidence":"High","gaps":["Cell-type-specific vulnerability of motor neurons not mechanistically explained","Whether aggregation or loss of degradation is the primary toxicity driver remained unclear"]},{"year":2020,"claim":"Demonstrating that NEMF knockdown impairs axonal outgrowth and synapse development in primary neurons provided a cellular correlate for the motor neuron disease phenotype.","evidence":"siRNA knockdown in mouse primary cortical neurons with immunofluorescence imaging","pmids":["33048237"],"confidence":"Medium","gaps":["Single knockdown study without rescue","Downstream molecular pathways linking RQC to axonogenesis not identified"]},{"year":2021,"claim":"Identification of CRL2-KLHDC10 and Pirh2 as E3 ligases that directly bind Ala-tailed substrates established a Listerin-independent, C-end rule degradation pathway downstream of NEMF-mediated CAT tailing.","evidence":"Biochemical pulldowns, in vitro ubiquitination reconstitution, and mutational analysis of the NEMF tRNA-Ala binding domain","pmids":["33909987"],"confidence":"High","gaps":["Relative contributions of C-end rule versus Listerin pathway in different tissues not determined","Whether other C-terminal amino acid compositions engage additional E3 ligases unknown"]},{"year":2021,"claim":"Showing that the nascent polypeptide sequence within the exit tunnel determines NEMF dependency for RQC defined substrate-intrinsic determinants that modulate CAT tailing.","evidence":"Yeast in vivo reporter assays for CAT tailing and ubiquitination with polytryptophan sequence variants","pmids":["33511411"],"confidence":"Medium","gaps":["Rules for mammalian tunnel-sequence effects not tested","Structural basis for tunnel-sequence inhibition of CAT tailing not resolved"]},{"year":2024,"claim":"Discovery that NEMF mediates an organelle-specific mitochondrial RQC pathway, where Ala-tailed mitochondrial nascent chains are cleared by Pirh2 and ClpXP protease, extended the CAT tail degron concept to organelle-targeted substrates.","evidence":"Co-immunoprecipitation, mitochondrial fractionation, in vivo reporters, and NEMF mutant analysis","pmids":["38412092"],"confidence":"High","gaps":["How Ala-tailed substrates are handed off from cytosolic Pirh2 to matrix ClpXP is unclear","Whether other mitochondrial proteases contribute is untested"]},{"year":2024,"claim":"NEMF-mutant mouse models revealed that disease-associated mutations disrupt Importin-β nuclear import and cause cytoplasmic TDP-43 mislocalization, connecting RQC failure to nucleocytoplasmic transport defects seen in other neurodegenerative diseases.","evidence":"Co-immunoprecipitation, immunofluorescence, and pharmacological inhibition of Importin-β in two mouse models and human cells","pmids":["39312574"],"confidence":"Medium","gaps":["Whether nucleocytoplasmic transport disruption is a direct or indirect consequence of RQC failure is unresolved","Causal relationship between TDP-43 mislocalization and motor neuron death not established"]},{"year":2025,"claim":"A genome-wide CRISPR screen revealed that NEMF-mediated CAT tailing is required for translocation-associated quality control at the ER, with AT-rich tails routing nonstop substrates through an unconventional Golgi-retrieval ERAD pathway and AG-rich tails directing substrates to lysosomal degradation.","evidence":"Genome-wide CRISPR screen, live-cell imaging, biochemical degradation assays, and CAT-tail mimetic analysis","pmids":["40257401"],"confidence":"High","gaps":["Receptor(s) that distinguish AT- versus AG-rich tails for routing decisions not identified","Whether this pathway operates on endogenous ER-stalled substrates in vivo is untested"]},{"year":2025,"claim":"A cryo-EM structure of the yeast RQC complex with a disease-relevant Rqc2 mutation elucidated how this mutation disrupts A-site tRNA binding in the presence of Ltn1, mechanistically linking impaired CAT tailing to genetic peptide-release defects.","evidence":"Cryo-EM structure, genetic screen, and functional peptide-release and CAT-tailing assays in yeast","pmids":["40187343"],"confidence":"High","gaps":["Structure of the mammalian NEMF–LTN1 complex at equivalent resolution not yet available","Whether peptide release defects contribute to disease pathology in mammals is untested"]},{"year":null,"claim":"Key unresolved questions include why motor neurons are selectively vulnerable to NEMF loss-of-function, whether aggregation toxicity or degradation failure is the primary driver of neurodegeneration, and how CAT tail composition (Ala, Thr, mixed) is decoded by distinct downstream E3 ligases and trafficking pathways to determine substrate fate.","evidence":"","pmids":[],"confidence":"High","gaps":["Tissue-specific proteomics of NEMF-dependent CAT-tailed substrates not performed","No therapeutic intervention targeting the CAT-tailing or RQC pathway has been reported","Full mammalian structural model of the NEMF–60S–LTN1–TCF25 complex is lacking"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[0,1,5,14]},{"term_id":"GO:0045182","term_label":"translation regulator activity","supporting_discovery_ids":[1,5,7,8,13]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,7,11]}],"localization":[{"term_id":"GO:0005840","term_label":"ribosome","supporting_discovery_ids":[0,7,14,15]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[5,10]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[8,9]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[13,15]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,1,5,7,8,13,14]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[6,7]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[3,10]}],"complexes":["Ribosome quality control (RQC) complex"],"partners":["LTN1","KLHDC10","PIRH2","TCF25","ANKZF1","CLPX","IMPORTIN-Β"],"other_free_text":[]},"mechanistic_narrative":"NEMF is the central scaffolding and catalytic subunit of the ribosome-associated quality control (RQC) complex, where it binds stalled 60S ribosomal subunits by simultaneously contacting the ribosome surface and peptidyl-tRNA, thereby sensing nascent-chain occupancy and recruiting the E3 ubiquitin ligase Listerin (LTN1) for ubiquitylation of aberrant translation products [PMID:25578875, PMID:35452614]. Independent of Listerin, NEMF appends C-terminal alanine-rich extensions (CAT tails) to stalled nascent chains via tRNA-Ala binding; these tails expose ribosome-buried lysines for ubiquitylation, serve as direct degrons recognized by the CRL2-KLHDC10 and Pirh2 E3 ligases through the C-end rule pathway, direct mitochondrial stalled nascent chains to ClpXP-mediated degradation, and route ER translocon-clogging nonstop substrates through an unconventional ERAD pathway involving Golgi retrieval [PMID:33909987, PMID:38412092, PMID:40257401]. When RQC-mediated degradation fails, NEMF-dependent CAT tails promote amyloid-like aggregation of undegraded substrates, and loss-of-function NEMF mutations cause progressive motor neuron degeneration in mice and juvenile neuromuscular disease in humans [PMID:32934225, PMID:26943317]. Disease-associated NEMF mutations additionally disrupt Importin-β-dependent nucleocytoplasmic transport with cytoplasmic mislocalization of TDP-43 and nuclear transport factors [PMID:39312574]."},"prefetch_data":{"uniprot":{"accession":"O60524","full_name":"Ribosome quality control complex subunit NEMF","aliases":["Antigen NY-CO-1","Nuclear export mediator factor","Serologically defined colon cancer antigen 1"],"length_aa":1076,"mass_kda":123.0,"function":"Key component of the ribosome quality control complex (RQC), a ribosome-associated complex that mediates the extraction of incompletely synthesized nascent chains from stalled ribosomes as well as their ubiquitin-mediated proteasomal degradation (PubMed:25578875, PubMed:32726578, PubMed:33406423, PubMed:33909987). Thereby, frees 60S subunit ribosomes from the stalled translation complex and prevents the accumulation of nascent polypeptide chains that are potentially toxic for the cell (PubMed:25578875, PubMed:33406423, PubMed:33909987). Within the RQC complex, NEMF specifically binds stalled 60S ribosomal subunits by recognizing an exposed, nascent chain-conjugated tRNA moiety and promotes the recruitment of LTN1 to stalled 60S subunits (PubMed:25578875). Following binding to stalled 60S ribosomal subunits, NEMF mediates CAT tailing by recruiting alanine-charged tRNA to the A-site and directing the elongation of stalled nascent chains independently of mRNA or 40S subunits, leading to non-templated C-terminal alanine extensions (CAT tails) (PubMed:33406423, PubMed:33909987). Mainly recruits alanine-charged tRNAs, but can also other amino acid-charged tRNAs (PubMed:33406423, PubMed:33909987). CAT tailing is required to promote ubiquitination of stalled nascent chains by different E3 ubiquitin-protein ligases (PubMed:33909987). In the canonical RQC pathway (RQC-L), CAT tailing facilitates LTN1-dependent ubiquitination by exposing lysine residues that would otherwise remain buried in the ribosomal exit tunnel (By similarity). In the alternative RQC pathway (RQC-C) CAT tailing creates an C-degron mainly composed of alanine that is recognized by the CRL2(KLHDC10) and RCHY1/PIRH2 E3 ligases, leading to ubiquitination and degradation of stalled nascent chains (PubMed:33909987). NEMF may also indirectly play a role in nuclear export (PubMed:16103875)","subcellular_location":"Cytoplasm, cytosol; Nucleus","url":"https://www.uniprot.org/uniprotkb/O60524/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/NEMF","classification":"Not Classified","n_dependent_lines":145,"n_total_lines":1208,"dependency_fraction":0.12003311258278146},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000165525","cell_line_id":"CID001825","localizations":[{"compartment":"cytoplasmic","grade":3}],"interactors":[{"gene":"EZR","stoichiometry":0.2},{"gene":"RPS16","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001825","total_profiled":1310},"omim":[{"mim_id":"619099","title":"INTELLECTUAL DEVELOPMENTAL DISORDER WITH SPEECH DELAY AND AXONAL PERIPHERAL NEUROPATHY; IDDSAPN","url":"https://www.omim.org/entry/619099"},{"mim_id":"608378","title":"NUCLEAR EXPORT MEDIATOR FACTOR; NEMF","url":"https://www.omim.org/entry/608378"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"},{"location":"Nuclear bodies","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/NEMF"},"hgnc":{"alias_symbol":["NY-CO-1","FLJ10051","RQC2"],"prev_symbol":["SDCCAG1"]},"alphafold":{"accession":"O60524","domains":[{"cath_id":"2.30.310.10","chopping":"8-158","consensus_level":"high","plddt":88.0572,"start":8,"end":158},{"cath_id":"-","chopping":"247-307","consensus_level":"medium","plddt":81.5751,"start":247,"end":307},{"cath_id":"-","chopping":"528-649","consensus_level":"medium","plddt":90.062,"start":528,"end":649},{"cath_id":"-","chopping":"651-673_979-1076","consensus_level":"medium","plddt":85.5187,"start":651,"end":1076},{"cath_id":"1.10.238","chopping":"168-242","consensus_level":"high","plddt":79.6495,"start":168,"end":242},{"cath_id":"1.10.287","chopping":"308-415_452-522","consensus_level":"medium","plddt":87.2554,"start":308,"end":522}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O60524","model_url":"https://alphafold.ebi.ac.uk/files/AF-O60524-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O60524-F1-predicted_aligned_error_v6.png","plddt_mean":69.69},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=NEMF","jax_strain_url":"https://www.jax.org/strain/search?query=NEMF"},"sequence":{"accession":"O60524","fasta_url":"https://rest.uniprot.org/uniprotkb/O60524.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O60524/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O60524"}},"corpus_meta":[{"pmid":"26943317","id":"PMC_26943317","title":"The Rqc2/Tae2 subunit of the ribosome-associated quality control (RQC) complex marks ribosome-stalled nascent polypeptide chains for aggregation.","date":"2016","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/26943317","citation_count":121,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"32934225","id":"PMC_32934225","title":"NEMF mutations that impair ribosome-associated quality control are associated with neuromuscular disease.","date":"2020","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/32934225","citation_count":84,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"33048237","id":"PMC_33048237","title":"Biallelic loss-of-function variants in NEMF cause central nervous system impairment and axonal polyneuropathy.","date":"2020","source":"Human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/33048237","citation_count":22,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"33511411","id":"PMC_33511411","title":"The nascent 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tails'), and this CATylation mediates formation of detergent-insoluble protein aggregates; Rqc2 also stabilizes binding of the E3 ligase Listerin/Ltn1 to the RQC complex.\",\n      \"method\": \"Genetic inactivation of Ltn1, biochemical fractionation for detergent-insoluble aggregates, yeast RQC complex reconstitution, mutant analyses\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods, highly cited foundational study replicated across labs\",\n      \"pmids\": [\"26943317\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"NEMF/Rqc2 disease-associated mutations selectively impair its ability to modify aberrant translation products with C-terminal tails (CAT-tailing), which normally assist RQC-mediated protein degradation, leading to progressive motor neuron degeneration in mice; NEMF is thus required for translational homeostasis in the nervous system.\",\n      \"method\": \"Three independently-generated mouse models with NEMF mutations, equivalent yeast Rqc2 mutations with RQC functional assays, patient exome sequencing with functional inference\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple independent mouse models with defined cellular phenotype, mechanistic pathway placement confirmed in yeast\",\n      \"pmids\": [\"32934225\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Knockdown of NEMF in cultured mouse primary cortical neurons impairs axonal outgrowth and synapse development, demonstrating a role for NEMF in mammalian neuron development.\",\n      \"method\": \"Immunofluorescence, shRNA knockdown in primary cortical neurons\",\n      \"journal\": \"Human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single lab, loss-of-function with defined cellular phenotype but no upstream pathway placement\",\n      \"pmids\": [\"33048237\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The nascent polypeptide sequence within the ribosome exit tunnel modulates Rqc2 (NEMF ortholog) activity: polytryptophan sequences (≥11 residues) proximal to the peptidyl transferase center inhibit CAT-tailing and induce an Rqc2-independent RQC pathway, while ≥8 tryptophan residues near the center block CAT-tailing triggered by tandem CGA codons.\",\n      \"method\": \"Yeast genetic assays, ribosome stalling reporters with defined polypeptide sequences, ubiquitination assays\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — epistasis and defined substrate-structure requirements, single lab\",\n      \"pmids\": [\"33511411\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In mammalian cells, NEMF mediates a Listerin-independent mitochondrial RQC pathway: NEMF appends C-terminal poly-alanine modifications to ribosome-stalled nuclear-encoded mitochondrial nascent polypeptides, which are then recognized by cytosolic E3 ligase Pirh2 and the mitochondrial protease ClpXP for coordinated clearance; defects cause NEMF-mediated aggregates and mitochondrial integrity failure.\",\n      \"method\": \"Co-immunoprecipitation, in vitro ubiquitination assays, MS/MS identification of CES modifications, siRNA knockdown with functional readouts (mitochondrial integrity, aggregation)\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods including in vitro assays and MS/MS in a single study\",\n      \"pmids\": [\"38412092\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In NEMF mutant mice (NemfR86S and NemfR487G), an Importin-β-specific nuclear import block occurs, causing cytoplasmic mis-localization and aggregation of TDP43, Importin-β, RanGAP1, and Ran; a pathological interaction between Importin-β and mutant NEMFR86S protein in cytoplasmic accumulations was detected.\",\n      \"method\": \"Mouse models (NemfR86S, NemfR487G), co-immunoprecipitation, immunofluorescence, pharmacological Importin-β inhibition in mouse and human neuronal cells\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — two mouse models with reciprocal Co-IP and imaging, single lab\",\n      \"pmids\": [\"39312574\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"NEMF-mediated CAT-tailing of stalled nonstop (NS) nascent chains at the ER translocon targets a subset of TAQC substrates through an unconventional ERAD mechanism involving ER-to-Golgi trafficking and KDEL-mediated substrate retrieval at the Golgi; an AT-rich CAT tail acts as a degron for ERAD while an AG-rich tail directs substrates to the lysosome.\",\n      \"method\": \"Genome-wide CRISPR screen, live-cell imaging, NEMF knockout/knockdown with ER stalling reporters, CAT-tail mimetics, lysosome/proteasome inhibitor assays\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — genome-wide CRISPR screen plus multiple orthogonal mechanistic assays in a single study\",\n      \"pmids\": [\"40257401\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Cryo-EM structure of the yeast RQC complex shows that the Rqc2 F340I mutation alters its binding to the 60S subunit, disrupting the A-site's ability to bind tRNA in the presence of Ltn1, thereby limiting CAT-tailing; Rqc2 contributes to peptide release from stalled ribosomes.\",\n      \"method\": \"Cryo-EM structure determination, genetic screen for rqc2 mutant alleles, in vivo CAT-tailing assays\",\n      \"journal\": \"Structure\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structure with mutagenesis and functional validation\",\n      \"pmids\": [\"40187343\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"NEMF binds to the large (60S) ribosomal subunit and recruits the E3 ubiquitin ligase Listerin to ubiquitinate stalled nascent chains; NEMF additionally extends the nascent chain's C-terminus with poly-alanine ('Ala-tail'), which exposes lysines in the ribosomal exit tunnel for ubiquitination. Selectively impairing NEMF's Ala-tailing activity in mice causes a synthetic lethal interaction with Listerin mutation, and partial reduction of Ala-tailing capacity markedly improves the lister neurodegeneration phenotype; RQC substrates that evade degradation form amyloid-like aggregates in an Ala-tail-dependent manner.\",\n      \"method\": \"Knock-in mouse models with selective Ala-tailing impairment, genetic interaction (double mutant) analysis, aggregate biochemistry\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis in multiple mouse models with defined biochemical phenotype (amyloid-like aggregates), strong mechanistic evidence\",\n      \"pmids\": [\"bio_10.1101_2024.08.24.608776\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"TCF25 (Rqc1 in yeast) interacts with the RING domain of Listerin and the acceptor ubiquitin to impose K48-specificity on Listerin-mediated ubiquitination of nascent chains; NEMF on 60S RNCs promotes recruitment of Listerin in this complex.\",\n      \"method\": \"Biochemical reconstitution, AlphaFold3 modeling, functional ubiquitination assays with Ube2D E2s\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — biochemical reconstitution with structural modeling, but preprint and NEMF's role is supporting context\",\n      \"pmids\": [\"bio_10.1101_2024.10.17.618946\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Canonical RQC factors including NEMF and LTN1 associate with ER-bound stalled ribosomes; UFMylation of RPL26 persists without late RQC components NEMF and LTN1, and UFMylation acts in concert with the canonical RQC pathway to facilitate clearance of arrested polypeptides at the ER.\",\n      \"method\": \"Functional cellular assays with ER-targeted stalling reporters, siRNA knockdown of NEMF and LTN1, UFMylation assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — defined epistatic relationship between UFMylation and NEMF/LTN1 using reporters and knockdowns, preprint\",\n      \"pmids\": [\"bio_10.1101_2025.01.17.633636\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"NEMF (mammalian ortholog of yeast Rqc2/Tae2) is a core component of the ribosome-associated quality control (RQC) complex that binds stalled 60S ribosomal subunits, recruits the E3 ligase Listerin to ubiquitinate incomplete nascent polypeptide chains, and appends non-templated C-terminal poly-alanine (CAT/Ala) tails to stalled chains—exposing lysines for ubiquitination, directing substrates to proteasomal or lysosomal degradation, or promoting aggregation when degradation fails—with additional Listerin-independent roles in mitochondrial and ER translocation-associated quality control, and whose dysfunction causes neurodegeneration linked to impaired CAT-tailing and nucleocytoplasmic transport defects.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2015,\n      \"finding\": \"NEMF is required for Listerin's specificity toward nascent chain-containing 60S subunits. Cryo-EM structure at 3.6 Å of the nascent chain-60S-Listerin-NEMF complex showed that NEMF makes simultaneous contacts with the 60S ribosomal subunit and peptidyl-tRNA to sense nascent chain occupancy, while ribosome-bound NEMF recruits and stabilizes Listerin's N-terminal domain; Listerin's C-terminal RWD domain directly contacts the ribosome to position its ligase domain near the nascent polypeptide exit tunnel.\",\n      \"method\": \"Cryo-EM structure determination (3.6 Å), structural and mutational analyses, in vitro reconstitution\",\n      \"journal\": \"Molecular Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structure plus mutagenesis in a single rigorous study\",\n      \"pmids\": [\"25578875\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Rqc2/Tae2 (NEMF ortholog in yeast) modifies ribosome-stalled nascent polypeptide chains with C-terminal Ala- and Thr-containing extensions ('CAT tails'), and CATylation mediates formation of detergent-insoluble protein aggregates; inefficient ubiquitination by Ltn1 (Listerin) favors this Rqc2-mediated aggregation reaction.\",\n      \"method\": \"Genetic epistasis (Ltn1 inactivation), biochemical fractionation (detergent-insolubility assay), in vivo labeling of nascent chains in yeast\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal genetic and biochemical methods; highly cited foundational study\",\n      \"pmids\": [\"26943317\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"ANKZF1 (yeast Vms1p) releases ubiquitinated nascent proteins from 60S ribosomal subunits during RQC; NEMF-mediated CAT tailing functions upstream of this release step. Cell-free reconstitution showed ANKZF1/Vms1p cleave polypeptidyl-tRNAs at the 3'CCA terminus on RQC complexes, and tRNA recycling requires TRNT1.\",\n      \"method\": \"Cell-free reconstitution system, biochemical cleavage assays\",\n      \"journal\": \"Nature Structural & Molecular Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 in vitro reconstitution but NEMF's role is contextual/upstream rather than directly assayed\",\n      \"pmids\": [\"31011209\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Three independently generated mouse models with mutations in NEMF/Rqc2 develop progressive motor neuron degeneration; equivalent mutations in yeast Rqc2 selectively interfere with C-terminal tail modification of aberrant translation products, implicating defective RQC-mediated protein degradation as the pathomechanism. Human NEMF mutations from seven families presenting juvenile neuromuscular disease were identified.\",\n      \"method\": \"Mouse genetic models (three independent lines), yeast genetics, human exome sequencing\",\n      \"journal\": \"Nature Communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — three independent mouse models plus yeast functional validation replicated across multiple families\",\n      \"pmids\": [\"32934225\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Knockdown of Nemf in cultured mouse primary cortical neurons impairs axonal outgrowth and synapse development, demonstrating NEMF is required for mammalian neuron development.\",\n      \"method\": \"siRNA knockdown in primary cortical neurons, immunofluorescence imaging of axonal morphology and synaptic markers\",\n      \"journal\": \"Human Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — KD with defined cellular phenotype in primary neurons, single study\",\n      \"pmids\": [\"33048237\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Mammalian NEMF has a Listerin-independent proteolytic role mediated by tRNA-Ala binding and alanine tailing; Ala tails signal proteolysis indirectly through the C-end rule pathway, with CRL2KLHDC10 E3 ligase complex and Pirh2/Rchy1 identified as E3 ligases that directly bind Ala-tailed ribosome stalling products and target them for degradation.\",\n      \"method\": \"Biochemical pulldowns, co-immunoprecipitation, in vitro ubiquitination assays, mutational analysis of NEMF tRNA-Ala binding domain, cell-based degradation assays\",\n      \"journal\": \"Molecular Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal biochemical methods including in vitro ubiquitination reconstitution and mutagenesis\",\n      \"pmids\": [\"33909987\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The nascent polypeptide sequence in the 60S ribosomal exit tunnel determines Rqc2 (NEMF ortholog) dependency for RQC; polytryptophan sequences (≥11 residues) induce Rqc2-independent RQC not coupled with CAT tailing, while eight consecutive tryptophan residues proximal to the peptidyl transferase center inhibit CAT tailing triggered by tandem CGA codons.\",\n      \"method\": \"Yeast genetics, in vivo reporter assays for CAT tailing and ubiquitination, mutant analysis\",\n      \"journal\": \"Nucleic Acids Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with multiple reporters but single lab\",\n      \"pmids\": [\"33511411\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"NEMF and its orthologs (yeast Rqc2, bacterial RqcH) are central RQC players that sense large ribosomal subunits obstructed with nascent chains, promote nascent-chain proteolysis by stabilizing LTN1/Listerin binding, and mediate C-terminal untemplated polypeptide elongation (CAT/Ala tailing) to expose ribosome-buried lysines for ubiquitination; C-terminal tails also function as extra-ribosomal degrons across evolution.\",\n      \"method\": \"Review synthesizing structural, biochemical, and genetic data from multiple studies\",\n      \"journal\": \"Molecular Cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — synthesis of multiple orthogonal studies, but review article\",\n      \"pmids\": [\"35452614\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"NEMF mediates a Listerin-independent, organelle-specific mitochondrial RQC pathway: mitochondrial nascent polypeptides stalled at the ribosome receive NEMF-mediated C-terminal poly-alanine modifications, which are then recognized by cytosolic E3 ligase Pirh2 and the mitochondrial ClpXP protease to coordinately clear the stalled chains; defects in this pathway cause NEMF-mediated protein aggregates and mitochondrial integrity failure.\",\n      \"method\": \"Co-immunoprecipitation, biochemical fractionation, in vivo reporter assays for mitochondrial RQC, NEMF mutant analysis, protease activity assays\",\n      \"journal\": \"Cell Reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods identifying a novel organelle-specific pathway with functional validation\",\n      \"pmids\": [\"38412092\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"A tandem MS/MS protocol using customized spectral database searching was developed to identify NEMF-mediated C-terminal extended sequences (CESs) on ribosome-stalled mitochondrial nascent chains, demonstrating that NEMF appends compositionally diverse C-terminal extensions beyond canonical poly-alanine.\",\n      \"method\": \"Tandem mass spectrometry (MS/MS) with customized spectral database, sample preparation from mitochondrial fractions\",\n      \"journal\": \"STAR Protocols\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct biochemical identification of NEMF-modified peptides by MS, methodological/protocol paper\",\n      \"pmids\": [\"39395174\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"NEMF mutant mouse models (NemfR86S and NemfR487G) display an Importin-β-specific nuclear import block, cytoplasmic mislocalization and aggregation of TDP43, Importin-β, RanGAP1, and Ran, and a pathological physical interaction between Importin-β and mutant NEMFR86S protein in cytoplasmic accumulations, suggesting that NEMF mutations cause neurodegeneration partly through disruption of nucleocytoplasmic transport.\",\n      \"method\": \"Mouse genetic models, co-immunoprecipitation, immunofluorescence localization, pharmacological inhibition of Importin-β in mouse and human cells\",\n      \"journal\": \"PLoS Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP and localization with functional consequence in two mouse models plus human cells\",\n      \"pmids\": [\"39312574\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"TCF25 (Rqc1 in yeast) interacts with the RING domain of Listerin and the acceptor ubiquitin to impose K48 linkage specificity on Listerin-mediated ubiquitination of nascent chains on 60S RNCs that associate with NEMF; NEMF promotes 60S RNC association with Listerin upstream of this TCF25-dependent step.\",\n      \"method\": \"Biochemical ubiquitination assays, co-immunoprecipitation, AlphaFold3 modeling\",\n      \"journal\": \"bioRxiv (preprint)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — functional biochemical reconstitution with structural modeling, but preprint only\",\n      \"pmids\": [\"bio_10.1101_2024.10.17.618946\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Selective impairment of NEMF's Ala-tailing activity in mice (homozygous Nemf mutation) causes mild motor defects but synthetic lethality when combined with the lister (Listerin) neurodegeneration mutation; conversely, partial reduction of Ala-tailing capacity (heterozygous Nemf mutation) markedly improves the lister phenotype. RQC substrates that evade degradation form amyloid-like aggregates in an Ala-tail-dependent fashion.\",\n      \"method\": \"Mouse genetic models, genetic epistasis (double mutant analysis), biochemical aggregation assays (amyloid-like aggregate characterization)\",\n      \"journal\": \"bioRxiv (preprint)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with multiple mouse models and biochemical aggregate characterization, but preprint\",\n      \"pmids\": [\"bio_10.1101_2024.08.24.608776\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"NEMF-mediated CAT tailing is required for translocation-associated quality control (TAQC) of nonstop (NS) mRNA-encoded nascent chains stalled during co-translational translocation at the ER. An AT-rich CAT tail functions as a degron directing substrates through an unconventional ERAD mechanism involving ER-to-Golgi trafficking and KDEL-mediated retrieval at the Golgi, while an AG-rich tail directs secretory proteins to the lysosome.\",\n      \"method\": \"Genome-wide CRISPR screen, live-cell imaging, biochemical degradation assays, CAT-tail mimetic characterization\",\n      \"journal\": \"Journal of Cell Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — genome-wide CRISPR screen combined with live imaging and multiple biochemical assays in peer-reviewed publication\",\n      \"pmids\": [\"40257401\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A cryo-EM structure of the yeast RQC complex revealed how the F340I mutation in Rqc2 (NEMF ortholog) alters its binding to the 60S subunit, disrupting the A-site's ability to bind tRNA in the presence of Ltn1 and thereby limiting CAT tailing; a genetic screen identified this Rqc2 mutant allele as involved in peptide release from stalled ribosomes.\",\n      \"method\": \"Cryo-EM structure determination, genetic screen, functional assays for peptide release and CAT tailing\",\n      \"journal\": \"Structure\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structure with mutagenesis and functional genetic validation\",\n      \"pmids\": [\"40187343\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Canonical RQC factors including NEMF and LTN1 associate with ribosomes stalled at the ER; ribosome splitting is a prerequisite for UFMylation of RPL26 on ER-stalled ribosomes, but UFMylation persists without late RQC components NEMF and LTN1, indicating UFMylation acts in concert with but independently downstream of early RQC steps to clear arrested polypeptides.\",\n      \"method\": \"Functional cellular assays with ER-targeted stalling reporters, co-immunoprecipitation, genetic epistasis (knockout of RQC factors)\",\n      \"journal\": \"bioRxiv (preprint)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — epistasis and co-IP with defined reporters, but preprint\",\n      \"pmids\": [\"bio_10.1101_2025.01.17.633636\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"NEMF (nuclear export mediator factor) is the central scaffolding and tRNA-binding component of the eukaryotic ribosome-associated quality control (RQC) complex: it binds obstructed 60S ribosomal subunits by sensing both the ribosome surface and peptidyl-tRNA, recruits and stabilizes the E3 ubiquitin ligase Listerin for nascent-chain ubiquitylation, and independently appends C-terminal poly-alanine (and mixed Ala/Thr) tails to stalled nascent chains via tRNA-Ala binding; these CAT tails expose ribosome-buried lysines for Listerin-dependent ubiquitylation, serve as direct degrons recognized by alternative E3 ligases (CRL2KLHDC10, Pirh2) in a Listerin-independent C-end rule pathway, direct stalled mitochondrial nascent chains to ClpXP-mediated degradation, sort ER-translocon-clogging nonstop substrates through a Golgi-retrieval ERAD route, and—when degradation fails—drive amyloid-like protein aggregation; mutations in NEMF that impair these functions cause progressive motor neuron degeneration in mice and juvenile neuromuscular disease in humans.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"NEMF is a core component of the ribosome-associated quality control (RQC) complex that surveils stalled translation on 60S ribosomal subunits and directs incomplete nascent polypeptides for degradation. NEMF binds stalled 60S subunits, recruits the E3 ubiquitin ligase Listerin, and appends non-templated C-terminal poly-alanine extensions (CAT tails) to arrested nascent chains, thereby exposing lysine residues within the ribosomal exit tunnel for Listerin-mediated ubiquitination [PMID:26943317, PMID:40187343]. Beyond canonical cytosolic RQC, NEMF operates in Listerin-independent mitochondrial quality control—where Pirh2 and ClpXP clear CAT-tailed mitochondrial precursors—and in ER translocon-associated quality control, where the composition of the CAT tail (AT-rich versus AG-rich) routes substrates to ERAD or lysosomal degradation [PMID:38412092, PMID:40257401]. Loss-of-function mutations in NEMF that selectively impair CAT-tailing cause progressive motor neuron degeneration in mice and are linked to human neurodegenerative disease, with downstream pathology including amyloid-like aggregation of undegraded RQC substrates and Importin-β-dependent nucleocytoplasmic transport defects [PMID:32934225, PMID:39312574].\",\n  \"teleology\": [\n    {\n      \"year\": 2016,\n      \"claim\": \"Establishing that Rqc2/NEMF is the enzyme that appends CAT tails to stalled nascent chains and that this modification can drive protein aggregation when ubiquitin-mediated degradation by Ltn1 fails resolved the question of how non-templated extensions arise on RQC substrates and what their dual consequences are.\",\n      \"evidence\": \"Yeast genetic inactivation of Ltn1, biochemical fractionation for detergent-insoluble aggregates, reconstitution of the RQC complex\",\n      \"pmids\": [\"26943317\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether mammalian NEMF performs the same CATylation reaction was not yet shown\",\n        \"The structural basis for how Rqc2 binds the 60S subunit and positions tRNAs was unknown\",\n        \"Downstream degradation pathways for CAT-tailed substrates beyond proteasomal targeting were uncharacterized\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstrating that disease-associated NEMF mutations selectively abolish CAT-tailing and cause progressive motor neuron degeneration in mice established that NEMF-mediated translational quality control is essential for neuronal survival.\",\n      \"evidence\": \"Three independent NEMF-mutant mouse models, equivalent yeast Rqc2 mutant functional assays, human exome sequencing\",\n      \"pmids\": [\"32934225\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether neurodegeneration arises from toxic aggregation, loss of substrate clearance, or secondary pathways was unresolved\",\n        \"The cell-type specificity of NEMF requirement (motor neurons versus other neurons) was not explained mechanistically\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Showing that NEMF knockdown impairs axonal outgrowth and synapse development in primary cortical neurons extended its neuronal role beyond motor neurons and identified a developmental function.\",\n      \"evidence\": \"shRNA knockdown in mouse primary cortical neurons with immunofluorescence\",\n      \"pmids\": [\"33048237\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether the neurodevelopmental phenotype is CAT-tailing-dependent or reflects a separate NEMF function was not tested\",\n        \"No in vivo developmental data were provided\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Revealing that the nascent polypeptide sequence within the ribosome exit tunnel modulates Rqc2 CAT-tailing activity—with polytryptophan stretches inhibiting CATylation—showed that substrate identity determines whether RQC proceeds through Rqc2-dependent or -independent routes.\",\n      \"evidence\": \"Yeast genetic assays with defined stalling reporters and ubiquitination readouts\",\n      \"pmids\": [\"33511411\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether tunnel-based modulation of NEMF activity operates in mammalian cells was not tested\",\n        \"The alternative Rqc2-independent pathway was not molecularly defined\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identifying a Listerin-independent mitochondrial RQC branch in which NEMF CAT-tails nuclear-encoded mitochondrial precursors for clearance by Pirh2 and ClpXP established that NEMF's quality control function extends beyond the canonical cytosolic pathway.\",\n      \"evidence\": \"Co-immunoprecipitation, in vitro ubiquitination, MS/MS identification of C-terminal extensions, siRNA knockdown with mitochondrial integrity readouts in mammalian cells\",\n      \"pmids\": [\"38412092\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"How NEMF-modified precursors are handed off from cytosolic Pirh2 to mitochondrial ClpXP is mechanistically unclear\",\n        \"The relative contribution of this pathway versus canonical RQC in neurodegeneration was not assessed\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Demonstrating that NEMF mutant mice exhibit Importin-β-specific nuclear import blockade with cytoplasmic TDP-43 and RanGAP1 mislocalization revealed a secondary pathological consequence of NEMF dysfunction linking RQC failure to nucleocytoplasmic transport defects.\",\n      \"evidence\": \"Two NEMF-mutant mouse models, co-immunoprecipitation, immunofluorescence, pharmacological Importin-β inhibition in mouse and human neuronal cells\",\n      \"pmids\": [\"39312574\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether the Importin-β interaction with mutant NEMF is direct or mediated by aggregated substrates is unresolved\",\n        \"Causality between nuclear import defects and neurodegeneration was not established\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A cryo-EM structure of the yeast RQC complex showed how Rqc2 positions tRNA at the A-site of the 60S subunit for CAT-tailing and revealed that a disease-relevant mutation (F340I) disrupts tRNA binding in the presence of Ltn1, providing the first structural explanation for how NEMF coordinates with Listerin.\",\n      \"evidence\": \"Cryo-EM structure determination, genetic screening for rqc2 alleles, in vivo CAT-tailing assays in yeast\",\n      \"pmids\": [\"40187343\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"A mammalian NEMF–60S structure has not been determined\",\n        \"How Rqc2 contributes to peptide release from stalled ribosomes is structurally unresolved\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Discovery that NEMF-mediated CAT-tail composition dictates ER stalled-substrate fate—AT-rich tails serving as ERAD degrons and AG-rich tails routing substrates to the lysosome via ER-to-Golgi trafficking and KDEL retrieval—established that CAT tails are not merely ubiquitination facilitators but encode degradation-pathway information.\",\n      \"evidence\": \"Genome-wide CRISPR screen, live-cell imaging, NEMF knockout with ER stalling reporters, CAT-tail mimetics, lysosome/proteasome inhibitor assays\",\n      \"pmids\": [\"40257401\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"The mechanism by which different CAT-tail compositions are recognized by distinct sorting receptors is unknown\",\n        \"Whether CAT-tail composition similarly directs cytosolic or mitochondrial RQC substrate routing has not been tested\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: how NEMF activity is regulated in different cellular compartments (cytosol, ER, mitochondria), whether CAT-tail composition is deterministically controlled or stochastic, the structural basis for mammalian NEMF function, and the precise mechanism by which NEMF dysfunction leads to cell-type-specific neurodegeneration.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No mammalian NEMF–60S cryo-EM or crystal structure exists\",\n        \"Determinants controlling CAT-tail amino acid composition are unknown\",\n        \"Cell-type-specific vulnerability to NEMF loss remains mechanistically unexplained\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 4, 6, 7, 8]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 7, 9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 1, 4, 8]},\n      {\"term_id\": \"GO:0005840\", \"supporting_discovery_ids\": [0, 7, 9]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [6, 10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1, 4, 6, 7, 8]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [0, 4, 6]},\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"complexes\": [\n      \"RQC complex\"\n    ],\n    \"partners\": [\n      \"LTN1\",\n      \"TCF25\",\n      \"PIRH2\",\n      \"CLPXP\",\n      \"RPL26\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"NEMF is the central scaffolding and catalytic subunit of the ribosome-associated quality control (RQC) complex, where it binds stalled 60S ribosomal subunits by simultaneously contacting the ribosome surface and peptidyl-tRNA, thereby sensing nascent-chain occupancy and recruiting the E3 ubiquitin ligase Listerin (LTN1) for ubiquitylation of aberrant translation products [PMID:25578875, PMID:35452614]. Independent of Listerin, NEMF appends C-terminal alanine-rich extensions (CAT tails) to stalled nascent chains via tRNA-Ala binding; these tails expose ribosome-buried lysines for ubiquitylation, serve as direct degrons recognized by the CRL2-KLHDC10 and Pirh2 E3 ligases through the C-end rule pathway, direct mitochondrial stalled nascent chains to ClpXP-mediated degradation, and route ER translocon-clogging nonstop substrates through an unconventional ERAD pathway involving Golgi retrieval [PMID:33909987, PMID:38412092, PMID:40257401]. When RQC-mediated degradation fails, NEMF-dependent CAT tails promote amyloid-like aggregation of undegraded substrates, and loss-of-function NEMF mutations cause progressive motor neuron degeneration in mice and juvenile neuromuscular disease in humans [PMID:32934225, PMID:26943317]. Disease-associated NEMF mutations additionally disrupt Importin-β-dependent nucleocytoplasmic transport with cytoplasmic mislocalization of TDP-43 and nuclear transport factors [PMID:39312574].\",\n  \"teleology\": [\n    {\n      \"year\": 2015,\n      \"claim\": \"Establishing how NEMF senses ribosome-stalled nascent chains and recruits Listerin resolved the fundamental question of how the RQC complex achieves substrate specificity on 60S subunits.\",\n      \"evidence\": \"Cryo-EM structure at 3.6 Å of the 60S–NEMF–Listerin complex with mutagenesis and in vitro reconstitution\",\n      \"pmids\": [\"25578875\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for tRNA binding by NEMF not resolved in this complex\", \"Mechanism of CAT tailing not yet discovered\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Discovery that the NEMF ortholog Rqc2 appends untemplated C-terminal Ala/Thr tails to stalled nascent chains revealed a second, Listerin-independent function and linked failed degradation to toxic protein aggregation.\",\n      \"evidence\": \"Genetic epistasis with Ltn1, detergent-insolubility assays, and in vivo nascent chain labeling in yeast\",\n      \"pmids\": [\"26943317\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mammalian CAT tailing not yet demonstrated\", \"E3 ligases recognizing CAT tails as degrons not identified\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Three independent NEMF-mutant mouse lines developing progressive motor neuron degeneration, together with human family studies, established NEMF as a disease gene and linked impaired CAT tailing to neurodegeneration.\",\n      \"evidence\": \"Three mouse genetic models, yeast functional validation of orthologous mutations, and exome sequencing of seven human families\",\n      \"pmids\": [\"32934225\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cell-type-specific vulnerability of motor neurons not mechanistically explained\", \"Whether aggregation or loss of degradation is the primary toxicity driver remained unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstrating that NEMF knockdown impairs axonal outgrowth and synapse development in primary neurons provided a cellular correlate for the motor neuron disease phenotype.\",\n      \"evidence\": \"siRNA knockdown in mouse primary cortical neurons with immunofluorescence imaging\",\n      \"pmids\": [\"33048237\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single knockdown study without rescue\", \"Downstream molecular pathways linking RQC to axonogenesis not identified\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identification of CRL2-KLHDC10 and Pirh2 as E3 ligases that directly bind Ala-tailed substrates established a Listerin-independent, C-end rule degradation pathway downstream of NEMF-mediated CAT tailing.\",\n      \"evidence\": \"Biochemical pulldowns, in vitro ubiquitination reconstitution, and mutational analysis of the NEMF tRNA-Ala binding domain\",\n      \"pmids\": [\"33909987\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contributions of C-end rule versus Listerin pathway in different tissues not determined\", \"Whether other C-terminal amino acid compositions engage additional E3 ligases unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showing that the nascent polypeptide sequence within the exit tunnel determines NEMF dependency for RQC defined substrate-intrinsic determinants that modulate CAT tailing.\",\n      \"evidence\": \"Yeast in vivo reporter assays for CAT tailing and ubiquitination with polytryptophan sequence variants\",\n      \"pmids\": [\"33511411\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Rules for mammalian tunnel-sequence effects not tested\", \"Structural basis for tunnel-sequence inhibition of CAT tailing not resolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Discovery that NEMF mediates an organelle-specific mitochondrial RQC pathway, where Ala-tailed mitochondrial nascent chains are cleared by Pirh2 and ClpXP protease, extended the CAT tail degron concept to organelle-targeted substrates.\",\n      \"evidence\": \"Co-immunoprecipitation, mitochondrial fractionation, in vivo reporters, and NEMF mutant analysis\",\n      \"pmids\": [\"38412092\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How Ala-tailed substrates are handed off from cytosolic Pirh2 to matrix ClpXP is unclear\", \"Whether other mitochondrial proteases contribute is untested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"NEMF-mutant mouse models revealed that disease-associated mutations disrupt Importin-β nuclear import and cause cytoplasmic TDP-43 mislocalization, connecting RQC failure to nucleocytoplasmic transport defects seen in other neurodegenerative diseases.\",\n      \"evidence\": \"Co-immunoprecipitation, immunofluorescence, and pharmacological inhibition of Importin-β in two mouse models and human cells\",\n      \"pmids\": [\"39312574\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether nucleocytoplasmic transport disruption is a direct or indirect consequence of RQC failure is unresolved\", \"Causal relationship between TDP-43 mislocalization and motor neuron death not established\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A genome-wide CRISPR screen revealed that NEMF-mediated CAT tailing is required for translocation-associated quality control at the ER, with AT-rich tails routing nonstop substrates through an unconventional Golgi-retrieval ERAD pathway and AG-rich tails directing substrates to lysosomal degradation.\",\n      \"evidence\": \"Genome-wide CRISPR screen, live-cell imaging, biochemical degradation assays, and CAT-tail mimetic analysis\",\n      \"pmids\": [\"40257401\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptor(s) that distinguish AT- versus AG-rich tails for routing decisions not identified\", \"Whether this pathway operates on endogenous ER-stalled substrates in vivo is untested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A cryo-EM structure of the yeast RQC complex with a disease-relevant Rqc2 mutation elucidated how this mutation disrupts A-site tRNA binding in the presence of Ltn1, mechanistically linking impaired CAT tailing to genetic peptide-release defects.\",\n      \"evidence\": \"Cryo-EM structure, genetic screen, and functional peptide-release and CAT-tailing assays in yeast\",\n      \"pmids\": [\"40187343\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of the mammalian NEMF–LTN1 complex at equivalent resolution not yet available\", \"Whether peptide release defects contribute to disease pathology in mammals is untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include why motor neurons are selectively vulnerable to NEMF loss-of-function, whether aggregation toxicity or degradation failure is the primary driver of neurodegeneration, and how CAT tail composition (Ala, Thr, mixed) is decoded by distinct downstream E3 ligases and trafficking pathways to determine substrate fate.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Tissue-specific proteomics of NEMF-dependent CAT-tailed substrates not performed\", \"No therapeutic intervention targeting the CAT-tailing or RQC pathway has been reported\", \"Full mammalian structural model of the NEMF–60S–LTN1–TCF25 complex is lacking\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [0, 1, 5, 14]},\n      {\"term_id\": \"GO:0045182\", \"supporting_discovery_ids\": [1, 5, 7, 8, 13]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 7, 11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005840\", \"supporting_discovery_ids\": [0, 7, 14, 15]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [5, 10]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [8, 9]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [13, 15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1, 5, 7, 8, 13, 14]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [6, 7]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [3, 10]}\n    ],\n    \"complexes\": [\n      \"Ribosome quality control (RQC) complex\"\n    ],\n    \"partners\": [\n      \"LTN1\",\n      \"KLHDC10\",\n      \"PIRH2\",\n      \"TCF25\",\n      \"ANKZF1\",\n      \"CLPX\",\n      \"IMPORTIN-β\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}