{"gene":"SMG5","run_date":"2026-06-10T07:46:35","timeline":{"discoveries":[{"year":2006,"finding":"Crystal structures of human SMG5 and SMG6 PIN domains reveal that SMG6 has the canonical acidic triad required for RNase H-type nuclease activity and can degrade single-stranded RNA in vitro, whereas SMG5 lacks key catalytic residues and has no intrinsic nuclease activity. An SMG6 with an inactive PIN domain acts as a dominant-negative inhibitor of NMD in Drosophila.","method":"X-ray crystallography, in vitro ssRNA degradation assay, Drosophila dominant-negative genetics","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structures plus in vitro enzymatic assays plus mutagenesis plus in vivo functional validation across two species in a single study","pmids":["17053788"],"is_preprint":false},{"year":2003,"finding":"Human SMG5 (hSmg5/7a) co-purifies with UPF1, UPF2, UPF3X, SMG1, and the catalytic subunit of protein phosphatase 2A (PP2A), and is required for dephosphorylation of UPF1 (but not UPF2), indicating SMG5 recruits PP2A to UPF1. SMG5 is predominantly cytoplasmic in HEK293T cells.","method":"Co-purification/co-immunoprecipitation, Western blot phosphatase assay, subcellular fractionation/Western blot","journal":"RNA (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-purification plus functional phosphatase assay, replicated in parallel by C. elegans study (PMID:12554664)","pmids":["12554878"],"is_preprint":false},{"year":2003,"finding":"C. elegans SMG-5 interacts with SMG-7, SMG-2 (UPF1 ortholog), and both the structural (PR65) and catalytic subunits of PP2A, as determined by immunoprecipitation and yeast two-hybrid assays, directing PP2A to dephosphorylate SMG-2.","method":"Co-immunoprecipitation, yeast two-hybrid","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal IP and yeast two-hybrid, independently replicates mammalian findings (PMID:12554878)","pmids":["12554664"],"is_preprint":false},{"year":2013,"finding":"Crystal structure of C. elegans SMG5-SMG7 complex shows their 14-3-3-like domains heterodimerize in an unusual perpendicular back-to-back orientation. Heterodimerization increases affinity of the complex for phosphorylated UPF1, and the degradative activity of the SMG5-SMG7 complex resides in SMG7. Structure-based mutations that disrupt the interaction impair NMD in human cells.","method":"X-ray crystallography, in vitro binding assays, structure-based mutagenesis, human cell NMD reporter assays","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus mutagenesis plus functional NMD assays in human cells, multiple orthogonal methods in one study","pmids":["23348841"],"is_preprint":false},{"year":2014,"finding":"Using purified components reconstituted in vitro, the SMG5-SMG7 14-3-3-like heterodimer recognizes a short C-terminal phosphorylated segment of UPF1 (containing the last two Ser-Gln motifs) in a phospho-dependent manner, whereas SMG6 has both a weak phospho-dependent and a dominant phospho-independent interaction with UPF1 mediated by a low-complexity region bordering its 14-3-3-like domain and the UPF1 helicase domain and C-terminal tail. Crystal structure of SMG6 14-3-3-like domain confirms a phosphoserine-binding site.","method":"In vitro reconstitution with purified proteins, crystal structure, binding assays","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with purified components plus crystal structure plus mutagenesis in a single rigorous study","pmids":["25013172"],"is_preprint":false},{"year":2012,"finding":"PNRC2 preferentially forms a complex with SMG5 (not SMG6 or SMG7); SMG5 bridges UPF1 (via phospho-dependent interaction) to PNRC2, which then connects to the decapping factor Dcp1a. Downregulation of PNRC2 abolishes the SMG5-Dcp1a interaction. Tethering assays place UPF1, SMG5, and PNRC2 at the same step in NMD.","method":"Co-immunoprecipitation, siRNA knockdown, tethering assay, microarray","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP plus tethering assay plus knockdown in single lab; contradicted by PMID:29348139 which finds no SMG5-PNRC2 physical interaction","pmids":["23234702"],"is_preprint":false},{"year":2018,"finding":"An interaction between SMG5 and PNRC2 was not detected physically or functionally in NMD reporters; instead, UPF1 directly interacts with PNRC2 and triggers 5'-3' exonucleolytic decay in tethering assays. SMG5-SMG7 complex interaction and its functional requirement for NMD was confirmed. PNRC2 knockdown does not affect NMD reporter RNA levels.","method":"Co-immunoprecipitation, tethering assay, siRNA knockdown, NMD reporter assay","journal":"RNA (New York, N.Y.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (co-IP, tethering, knockdown reporters), single lab; contradicts PMID:23234702 on SMG5-PNRC2 interaction","pmids":["29348139"],"is_preprint":false},{"year":2021,"finding":"Loss of the SMG5-SMG7 pathway also inactivates the SMG6 endonucleolytic branch, demonstrating that SMG5-SMG7 recruitment is required to authorize/license SMG6-mediated cleavage. Either SMG5 or SMG7 alone is sufficient to support SMG6 endonucleolysis and activate NMD, revealing SMG5 can substitute for SMG7.","method":"siRNA knockdown of SMG5/SMG7, transcriptome-wide RNA-seq, NMD reporter assays in human cells","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — transcriptome-wide analysis combined with NMD reporter assays and genetic depletion experiments, multiple orthogonal methods, published in peer-reviewed journal","pmids":["34172724"],"is_preprint":false},{"year":2018,"finding":"In Drosophila, Smg5 is genetically essential for NMD activity, required for both SMG6-dependent endonucleolytic cleavage and an additional SMG6-independent degradation mechanism. Epistasis analysis shows Smg1 becomes essential for NMD when Smg5 function is partially compromised.","method":"Drosophila genetics, NMD reporter assays, epistasis analysis","journal":"Genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with defined NMD phenotypic readouts in Drosophila, single lab","pmids":["29903866"],"is_preprint":false},{"year":2026,"finding":"In C. elegans, the PIN domain of SMG-5, though catalytically inactive by canonical criteria, contains highly conserved residues essential for NMD. AlphaFold predicts a direct PIN-PIN interaction between SMG-5 and SMG-6, validated by in vitro pulldowns. Compensatory salt-bridge flip mutations confirm this interface is functionally required for SMG-6-mediated mRNA cleavage.","method":"AlphaFold structural prediction, in vitro pulldown, C. elegans genetic complementary mutagenesis, NMD reporter assays","journal":"RNA (New York, N.Y.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro pulldown plus in vivo compensatory mutagenesis, single lab, structural prediction not experimentally solved","pmids":["41638882"],"is_preprint":false},{"year":2026,"finding":"AlphaFold models predict a high-confidence SMG5-SMG6 PIN domain interface forming a composite active site, where a conserved SMG5 aspartate (D893) completes the canonical tetrad required for PIN-domain catalysis. In vitro, SMG6 alone has weak endonuclease activity that is enhanced ~10-fold by the addition of the SMG5 PIN domain. Mutations at the predicted interface, RNA-binding sites, or active site abolish this composite endonuclease activity and impair cellular NMD.","method":"AlphaFold structural prediction, in vitro reconstituted endonuclease assay, mutagenesis, cell-based NMD assay","journal":"Journal of molecular biology","confidence":"Medium","confidence_rationale":"Tier 1-2 / Moderate — in vitro biochemical reconstitution plus mutagenesis plus cellular NMD assay, single lab, structure predicted not experimentally solved","pmids":["41763597"],"is_preprint":false},{"year":2026,"finding":"SMG5 and SMG6 interact via their PIN domains to form a composite PIN (cPIN) heterodimer with full endonuclease activity. Reconstituted SMG5-SMG6 cPIN heterodimers show high in vitro activity; SMG5 completes the SMG6 active site and substrate binding site. Mutations at their predicted interaction surfaces, RNA-binding sites, or active site attenuate or abolish cPIN activity in vitro and impair cellular NMD.","method":"Structural predictions (AlphaFold), biochemical in vitro reconstitution, mutagenesis, cell-based NMD analysis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution plus mutagenesis plus cellular NMD assay, converges with two independent studies (PMIDs 41638882, 41763597) published concurrently","pmids":["41714610"],"is_preprint":false},{"year":2025,"finding":"Conditional knockout of Smg5 in mouse craniofacial neural crest cells causes abnormal accumulation of a PTC-containing Porcn transcript, leading to reduced Porcn protein and impaired Wnt5a/JNK signaling, resulting in hypoplastic mandibles, tongue mispositioning, and cleft palate. Wnt5a addition to SMG5-deficient CNC explants ameliorates cell death.","method":"Conditional knockout mouse model, transcriptome analysis, Western blot for Porcn, Wnt5a rescue in CNC explants","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO with mechanistic pathway placement via Porcn/Wnt5a, single lab, partially relies on transcriptome correlation for Porcn mechanism","pmids":["40071146"],"is_preprint":false},{"year":2024,"finding":"SMG5 knockout in mouse embryonic germ cells causes spermatogenesis failure (Sertoli cell-only phenotype) due to defective spermatogonial differentiation and maintenance. SMG5 loss leads to hyperactivation of the p38 MAPK signaling pathway causing widespread cell death during spermatogonial differentiation.","method":"Conditional knockout mouse model, transcriptome analysis, Western blot for p38 MAPK pathway components, histology","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO with defined cellular and molecular phenotype and pathway placement, single lab","pmids":["39704269"],"is_preprint":false},{"year":2024,"finding":"Smg5 knockout mESCs are viable but show delayed differentiation. SMG5 loss causes upregulation of c-MYC protein (but not c-Myc mRNA), attributed to enhanced protein synthesis, and dysregulates alternative splicing of stem cell differentiation regulators.","method":"Conditional knockout mESCs, Western blot, polysome profiling inference, transcriptome/alternative splicing analysis","journal":"Biomolecules","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO with defined molecular phenotype, single lab; mechanistic basis of c-MYC upregulation inferred rather than directly tested","pmids":["39199410"],"is_preprint":false},{"year":2025,"finding":"Conditional knockout of Smg5 in oligodendrocyte lineage cells impairs oligodendrocyte differentiation and myelination due to failure to degrade PTC-containing Hnrnpl variant transcripts. Excess HNRNPL disrupts alternative splicing of myelin-associated genes Mag and Nfasc.","method":"Conditional knockout mouse model, RNA analysis, Western blot, electron microscopy of myelin, motor function assays","journal":"The Journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO with defined NMD substrate (Hnrnpl), downstream splicing mechanism identified, single lab","pmids":["40930975"],"is_preprint":false}],"current_model":"SMG5 is a catalytically inactive PIN-domain and 14-3-3-like domain-containing NMD factor that functions primarily as a scaffold: its 14-3-3-like domain heterodimerizes with SMG7 to recognize phosphorylated UPF1 (at C-terminal SQ motifs) and recruit PP2A for UPF1 dephosphorylation, while its PIN domain directly interacts with the SMG6 PIN domain to complete a composite active site that licenses and enhances SMG6 endonuclease activity ~10-fold, thereby coupling UPF1 phosphorylation to downstream mRNA cleavage."},"narrative":{"mechanistic_narrative":"SMG5 is a core nonsense-mediated mRNA decay (NMD) factor that couples phosphorylation of the central NMD helicase UPF1 to downstream mRNA destruction [PMID:12554878, PMID:34172724]. Although its PIN domain lacks the canonical catalytic residues for RNase H-type nuclease activity, SMG5 itself has no intrinsic endonuclease function [PMID:17053788]. Instead, it acts as a bifunctional scaffold. Through its 14-3-3-like domain it heterodimerizes back-to-back with SMG7, and this heterodimer recognizes the C-terminal phosphorylated Ser-Gln motifs of UPF1 in a phospho-dependent manner [PMID:23348841, PMID:25013172]; SMG5 recruits protein phosphatase 2A to dephosphorylate UPF1, thereby resetting the UPF1 phosphorylation cycle [PMID:12554878, PMID:12554664]. The SMG5-SMG7 module additionally licenses the endonucleolytic branch of NMD, since loss of this pathway inactivates SMG6-mediated cleavage and either SMG5 or SMG7 alone suffices to authorize SMG6 endonucleolysis [PMID:34172724]. SMG5 further contributes directly to cleavage through its catalytically dead PIN domain, which docks onto the SMG6 PIN domain to form a composite active site in which a conserved SMG5 aspartate completes the catalytic tetrad, enhancing SMG6 endonuclease activity ~10-fold [PMID:41763597, PMID:41714610]. In vivo, SMG5-dependent NMD is essential for clearing PTC-containing transcripts; conditional loss in mouse tissues stabilizes specific substrates and disrupts development, including a Porcn/Wnt5a axis required for craniofacial morphogenesis [PMID:40071146] and an Hnrnpl-dependent splicing program required for oligodendrocyte myelination [PMID:40930975].","teleology":[{"year":2003,"claim":"Established SMG5's first defined molecular role: linking the NMD machinery to UPF1 dephosphorylation rather than acting as an autonomous enzyme.","evidence":"Co-purification/IP and phosphatase assays in human cells, replicated by yeast two-hybrid and IP in C. elegans","pmids":["12554878","12554664"],"confidence":"High","gaps":["Did not determine whether PP2A recruitment is direct or scaffolded through SMG7","Structural basis of phospho-UPF1 recognition unresolved"]},{"year":2006,"claim":"Resolved why SMG5 is not a nuclease: its PIN domain lacks the acidic catalytic triad present in the active SMG6 PIN domain, defining SMG5 as a non-catalytic NMD factor.","evidence":"X-ray crystallography of human SMG5/SMG6 PIN domains with in vitro ssRNA assays and Drosophila dominant-negative genetics","pmids":["17053788"],"confidence":"High","gaps":["Did not address whether the SMG5 PIN domain has any function despite lacking catalysis","No interaction tested between SMG5 and SMG6 PIN domains"]},{"year":2013,"claim":"Defined the structural logic of the SMG5-SMG7 module, showing 14-3-3-like heterodimerization is required for high-affinity phospho-UPF1 binding and for NMD.","evidence":"Crystal structure of C. elegans SMG5-SMG7 plus structure-based mutagenesis and human cell NMD reporters","pmids":["23348841"],"confidence":"High","gaps":["Degradative activity localized to SMG7, leaving SMG5's contribution to decay undefined","Did not address SMG6 branch coupling"]},{"year":2014,"claim":"Reconstituted phospho-dependent UPF1 recognition by purified SMG5-SMG7, distinguishing it from SMG6's largely phospho-independent UPF1 binding.","evidence":"In vitro reconstitution with purified proteins, crystallography of the SMG6 14-3-3-like domain, and binding assays","pmids":["25013172"],"confidence":"High","gaps":["Did not test functional consequences of the two recognition modes in cells","Did not address how SMG5-SMG7 and SMG6 binding are coordinated on UPF1"]},{"year":2012,"claim":"Proposed that SMG5 bridges phospho-UPF1 to decapping via PNRC2 and Dcp1a, placing SMG5 at a specific decay step.","evidence":"Co-IP, siRNA knockdown, tethering and microarray in a single lab","pmids":["23234702"],"confidence":"Medium","gaps":["Directly contradicted by a later study finding no SMG5-PNRC2 interaction","Single-lab interaction not independently reproduced"]},{"year":2018,"claim":"Challenged the SMG5-PNRC2 bridging model, reassigning PNRC2-driven 5'-3' decay to a direct UPF1-PNRC2 interaction while confirming the SMG5-SMG7 requirement.","evidence":"Co-IP, tethering, siRNA knockdown and NMD reporters","pmids":["29348139"],"confidence":"Medium","gaps":["Discrepancy with the earlier PNRC2 study not mechanistically resolved","Single-lab study"]},{"year":2018,"claim":"Demonstrated genetic essentiality of Smg5 for NMD in vivo, covering both SMG6-dependent and SMG6-independent decay routes.","evidence":"Drosophila genetics, NMD reporters and epistasis analysis","pmids":["29903866"],"confidence":"Medium","gaps":["Molecular identity of the SMG6-independent route not defined","Epistasis with Smg1 not extended to mammalian systems"]},{"year":2021,"claim":"Established that the SMG5-SMG7 pathway licenses the SMG6 endonucleolytic branch, with SMG5 able to substitute for SMG7.","evidence":"siRNA depletion of SMG5/SMG7 with transcriptome-wide RNA-seq and NMD reporters in human cells","pmids":["34172724"],"confidence":"High","gaps":["Did not define the physical basis of SMG6 licensing by SMG5","Did not determine redundancy mechanism between SMG5 and SMG7"]},{"year":2026,"claim":"Revealed the molecular basis of SMG6 licensing: the catalytically dead SMG5 PIN domain directly contacts the SMG6 PIN domain to form a composite active site that completes the catalytic tetrad and enhances cleavage ~10-fold.","evidence":"AlphaFold modeling, in vitro pulldowns and reconstituted endonuclease assays, compensatory mutagenesis and cellular NMD assays across C. elegans and human components, converging across three concurrent studies","pmids":["41638882","41763597","41714610"],"confidence":"High","gaps":["Composite PIN interface predicted by AlphaFold but not experimentally solved by crystallography or cryo-EM","Stoichiometry and regulation of cPIN assembly in cells undefined"]},{"year":2025,"claim":"Connected SMG5-dependent NMD to mammalian developmental programs by identifying tissue-specific PTC-containing substrates whose stabilization drives phenotypes.","evidence":"Conditional knockout mice in neural crest and oligodendrocyte lineages with transcriptome analysis, Western blot, rescue and histology (Porcn/Wnt5a; Hnrnpl/Mag/Nfasc)","pmids":["40071146","40930975","39704269","39199410"],"confidence":"Medium","gaps":["Some substrate-to-phenotype links rely on transcriptome correlation","c-MYC and p38 MAPK effects mechanistically inferred rather than fully reconstituted","Single-lab tissue models"]},{"year":null,"claim":"How phospho-UPF1 recognition by the SMG5-SMG7 14-3-3 module, PP2A recruitment, and assembly of the SMG5-SMG6 composite PIN are temporally coordinated on a single mRNP remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No integrated structure of UPF1-SMG5-SMG6/SMG7 on substrate","Order of dephosphorylation versus endonucleolytic licensing unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[3,7,11]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[10,11]},{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[4,10]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[1]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[1,7,11]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0]}],"complexes":["SMG5-SMG7 14-3-3-like heterodimer","SMG5-SMG6 composite PIN (cPIN) heterodimer"],"partners":["SMG7","SMG6","UPF1","PP2A","UPF2","UPF3X","SMG1","PNRC2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9UPR3","full_name":"Nonsense-mediated mRNA decay factor SMG5","aliases":["EST1-like protein B","LPTS-RP1","LPTS-interacting protein","SMG-5 homolog","hSMG-5"],"length_aa":1016,"mass_kda":113.9,"function":"Plays a role in nonsense-mediated mRNA decay. Does not have RNase activity by itself. Promotes dephosphorylation of UPF1. Together with SMG7 is thought to provide a link to the mRNA degradation machinery involving exonucleolytic pathways, and to serve as an adapter for UPF1 to protein phosphatase 2A (PP2A), thereby triggering UPF1 dephosphorylation. Necessary for TERT activity","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/Q9UPR3/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/SMG5","classification":"Common Essential","n_dependent_lines":1191,"n_total_lines":1208,"dependency_fraction":0.9859271523178808},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SMG5","total_profiled":1310},"omim":[{"mim_id":"616970","title":"MARVEL DOMAIN-CONTAINING PROTEIN 1; MARVELD1","url":"https://www.omim.org/entry/616970"},{"mim_id":"615531","title":"TRANSMEMBRANE PROTEIN 79; TMEM79","url":"https://www.omim.org/entry/615531"},{"mim_id":"610964","title":"SMG7 NONSENSE-MEDIATED mRNA DECAY FACTOR; SMG7","url":"https://www.omim.org/entry/610964"},{"mim_id":"610963","title":"SMG6 NONSENSE-MEDIATED mRNA DECAY FACTOR; SMG6","url":"https://www.omim.org/entry/610963"},{"mim_id":"610962","title":"SMG5 NONSENSE-MEDIATED mRNA DECAY FACTOR; SMG5","url":"https://www.omim.org/entry/610962"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Cytoplasmic bodies","reliability":"Supported"},{"location":"Plasma membrane","reliability":"Additional"},{"location":"Primary cilium","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SMG5"},"hgnc":{"alias_symbol":["KIAA1089","LPTS-RP1","LPTSRP1","RP11-54H19.7","SMG-5","EST1B"],"prev_symbol":[]},"alphafold":{"accession":"Q9UPR3","domains":[{"cath_id":"-","chopping":"646-745_757-799","consensus_level":"medium","plddt":90.9421,"start":646,"end":799},{"cath_id":"3.40.50.1010","chopping":"857-1016","consensus_level":"high","plddt":82.1671,"start":857,"end":1016}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UPR3","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UPR3-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UPR3-F1-predicted_aligned_error_v6.png","plddt_mean":72.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SMG5","jax_strain_url":"https://www.jax.org/strain/search?query=SMG5"},"sequence":{"accession":"Q9UPR3","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9UPR3.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9UPR3/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UPR3"}},"corpus_meta":[{"pmid":"17053788","id":"PMC_17053788","title":"Structures of the PIN domains of SMG6 and SMG5 reveal a nuclease within the mRNA surveillance complex.","date":"2006","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/17053788","citation_count":170,"is_preprint":false},{"pmid":"12554878","id":"PMC_12554878","title":"Characterization of human Smg5/7a: a protein with similarities to Caenorhabditis elegans SMG5 and SMG7 that functions in the dephosphorylation of Upf1.","date":"2003","source":"RNA (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/12554878","citation_count":135,"is_preprint":false},{"pmid":"12554664","id":"PMC_12554664","title":"SMG-5, required for C.elegans nonsense-mediated mRNA decay, associates with SMG-2 and protein phosphatase 2A.","date":"2003","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/12554664","citation_count":122,"is_preprint":false},{"pmid":"25013172","id":"PMC_25013172","title":"Phospho-dependent and phospho-independent interactions of the helicase UPF1 with the NMD factors SMG5-SMG7 and SMG6.","date":"2014","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/25013172","citation_count":90,"is_preprint":false},{"pmid":"23348841","id":"PMC_23348841","title":"An unusual arrangement of two 14-3-3-like domains in the SMG5-SMG7 heterodimer is required for efficient nonsense-mediated mRNA decay.","date":"2013","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/23348841","citation_count":79,"is_preprint":false},{"pmid":"34172724","id":"PMC_34172724","title":"SMG5-SMG7 authorize nonsense-mediated mRNA decay by enabling SMG6 endonucleolytic activity.","date":"2021","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/34172724","citation_count":73,"is_preprint":false},{"pmid":"23234702","id":"PMC_23234702","title":"SMG5-PNRC2 is functionally dominant compared with SMG5-SMG7 in mammalian nonsense-mediated mRNA decay.","date":"2012","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/23234702","citation_count":73,"is_preprint":false},{"pmid":"23788676","id":"PMC_23788676","title":"The RNA helicase Ddx5/p68 binds to hUpf3 and enhances NMD of Ddx17/p72 and Smg5 mRNA.","date":"2013","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/23788676","citation_count":31,"is_preprint":false},{"pmid":"29348139","id":"PMC_29348139","title":"Dissecting the functions of SMG5, SMG7, and PNRC2 in nonsense-mediated mRNA decay of human cells.","date":"2018","source":"RNA (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/29348139","citation_count":27,"is_preprint":false},{"pmid":"29903866","id":"PMC_29903866","title":"Multiple Nonsense-Mediated mRNA Processes Require Smg5 in Drosophila.","date":"2018","source":"Genetics","url":"https://pubmed.ncbi.nlm.nih.gov/29903866","citation_count":14,"is_preprint":false},{"pmid":"27473591","id":"PMC_27473591","title":"MicroRNA 433 regulates nonsense-mediated mRNA decay by targeting SMG5 mRNA.","date":"2016","source":"BMC molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/27473591","citation_count":10,"is_preprint":false},{"pmid":"40071146","id":"PMC_40071146","title":"Fine-tuning of Wnt signaling by RNA surveillance factor Smg5 in the mouse craniofacial development.","date":"2025","source":"iScience","url":"https://pubmed.ncbi.nlm.nih.gov/40071146","citation_count":6,"is_preprint":false},{"pmid":"39704269","id":"PMC_39704269","title":"SMG5, a component of nonsense-mediated mRNA decay, is essential for the mouse spermatogonial differentiation and maintenance.","date":"2024","source":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","url":"https://pubmed.ncbi.nlm.nih.gov/39704269","citation_count":5,"is_preprint":false},{"pmid":"39199410","id":"PMC_39199410","title":"RNA Surveillance Factor SMG5 Is Essential for Mouse Embryonic Stem Cell Differentiation.","date":"2024","source":"Biomolecules","url":"https://pubmed.ncbi.nlm.nih.gov/39199410","citation_count":4,"is_preprint":false},{"pmid":"38647536","id":"PMC_38647536","title":"SMG5 Inhibition Restrains Hepatocellular Carcinoma Growth and Enhances Sorafenib Sensitivity.","date":"2024","source":"Molecular cancer therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/38647536","citation_count":3,"is_preprint":false},{"pmid":"41638882","id":"PMC_41638882","title":"The PIN domain of SMG-5 functionally interacts with SMG-6 to stimulate NMD.","date":"2026","source":"RNA (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/41638882","citation_count":3,"is_preprint":false},{"pmid":"41763597","id":"PMC_41763597","title":"Active Site Assembly by SMG5 as a Mechanism for SMG6 Endonuclease Licencing in Nonsense-mediated mRNA Decay.","date":"2026","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/41763597","citation_count":3,"is_preprint":false},{"pmid":"40930975","id":"PMC_40930975","title":"Smg5 Enhances Oligodendrocyte Differentiation via Nonsense-Mediated mRNA Decay of Hnrnpl Variant Transcripts.","date":"2025","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/40930975","citation_count":2,"is_preprint":false},{"pmid":"41714610","id":"PMC_41714610","title":"Composite SMG5-SMG6 PIN domain formation is essential for NMD.","date":"2026","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/41714610","citation_count":2,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":10888,"output_tokens":4106,"usd":0.047127,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":11890,"output_tokens":3576,"usd":0.074425,"stage2_stop_reason":"end_turn"},"total_usd":0.121552,"stage1_batch_id":"msgbatch_013LWZZT6MWaqB9qyTSeQBmU","stage2_batch_id":"msgbatch_0194ZzQaTGNpruoNJBbEMbt3","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2006,\n      \"finding\": \"Crystal structures of human SMG5 and SMG6 PIN domains reveal that SMG6 has the canonical acidic triad required for RNase H-type nuclease activity and can degrade single-stranded RNA in vitro, whereas SMG5 lacks key catalytic residues and has no intrinsic nuclease activity. An SMG6 with an inactive PIN domain acts as a dominant-negative inhibitor of NMD in Drosophila.\",\n      \"method\": \"X-ray crystallography, in vitro ssRNA degradation assay, Drosophila dominant-negative genetics\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structures plus in vitro enzymatic assays plus mutagenesis plus in vivo functional validation across two species in a single study\",\n      \"pmids\": [\"17053788\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Human SMG5 (hSmg5/7a) co-purifies with UPF1, UPF2, UPF3X, SMG1, and the catalytic subunit of protein phosphatase 2A (PP2A), and is required for dephosphorylation of UPF1 (but not UPF2), indicating SMG5 recruits PP2A to UPF1. SMG5 is predominantly cytoplasmic in HEK293T cells.\",\n      \"method\": \"Co-purification/co-immunoprecipitation, Western blot phosphatase assay, subcellular fractionation/Western blot\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal co-purification plus functional phosphatase assay, replicated in parallel by C. elegans study (PMID:12554664)\",\n      \"pmids\": [\"12554878\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"C. elegans SMG-5 interacts with SMG-7, SMG-2 (UPF1 ortholog), and both the structural (PR65) and catalytic subunits of PP2A, as determined by immunoprecipitation and yeast two-hybrid assays, directing PP2A to dephosphorylate SMG-2.\",\n      \"method\": \"Co-immunoprecipitation, yeast two-hybrid\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal IP and yeast two-hybrid, independently replicates mammalian findings (PMID:12554878)\",\n      \"pmids\": [\"12554664\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Crystal structure of C. elegans SMG5-SMG7 complex shows their 14-3-3-like domains heterodimerize in an unusual perpendicular back-to-back orientation. Heterodimerization increases affinity of the complex for phosphorylated UPF1, and the degradative activity of the SMG5-SMG7 complex resides in SMG7. Structure-based mutations that disrupt the interaction impair NMD in human cells.\",\n      \"method\": \"X-ray crystallography, in vitro binding assays, structure-based mutagenesis, human cell NMD reporter assays\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus mutagenesis plus functional NMD assays in human cells, multiple orthogonal methods in one study\",\n      \"pmids\": [\"23348841\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Using purified components reconstituted in vitro, the SMG5-SMG7 14-3-3-like heterodimer recognizes a short C-terminal phosphorylated segment of UPF1 (containing the last two Ser-Gln motifs) in a phospho-dependent manner, whereas SMG6 has both a weak phospho-dependent and a dominant phospho-independent interaction with UPF1 mediated by a low-complexity region bordering its 14-3-3-like domain and the UPF1 helicase domain and C-terminal tail. Crystal structure of SMG6 14-3-3-like domain confirms a phosphoserine-binding site.\",\n      \"method\": \"In vitro reconstitution with purified proteins, crystal structure, binding assays\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with purified components plus crystal structure plus mutagenesis in a single rigorous study\",\n      \"pmids\": [\"25013172\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"PNRC2 preferentially forms a complex with SMG5 (not SMG6 or SMG7); SMG5 bridges UPF1 (via phospho-dependent interaction) to PNRC2, which then connects to the decapping factor Dcp1a. Downregulation of PNRC2 abolishes the SMG5-Dcp1a interaction. Tethering assays place UPF1, SMG5, and PNRC2 at the same step in NMD.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, tethering assay, microarray\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP plus tethering assay plus knockdown in single lab; contradicted by PMID:29348139 which finds no SMG5-PNRC2 physical interaction\",\n      \"pmids\": [\"23234702\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"An interaction between SMG5 and PNRC2 was not detected physically or functionally in NMD reporters; instead, UPF1 directly interacts with PNRC2 and triggers 5'-3' exonucleolytic decay in tethering assays. SMG5-SMG7 complex interaction and its functional requirement for NMD was confirmed. PNRC2 knockdown does not affect NMD reporter RNA levels.\",\n      \"method\": \"Co-immunoprecipitation, tethering assay, siRNA knockdown, NMD reporter assay\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (co-IP, tethering, knockdown reporters), single lab; contradicts PMID:23234702 on SMG5-PNRC2 interaction\",\n      \"pmids\": [\"29348139\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Loss of the SMG5-SMG7 pathway also inactivates the SMG6 endonucleolytic branch, demonstrating that SMG5-SMG7 recruitment is required to authorize/license SMG6-mediated cleavage. Either SMG5 or SMG7 alone is sufficient to support SMG6 endonucleolysis and activate NMD, revealing SMG5 can substitute for SMG7.\",\n      \"method\": \"siRNA knockdown of SMG5/SMG7, transcriptome-wide RNA-seq, NMD reporter assays in human cells\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — transcriptome-wide analysis combined with NMD reporter assays and genetic depletion experiments, multiple orthogonal methods, published in peer-reviewed journal\",\n      \"pmids\": [\"34172724\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"In Drosophila, Smg5 is genetically essential for NMD activity, required for both SMG6-dependent endonucleolytic cleavage and an additional SMG6-independent degradation mechanism. Epistasis analysis shows Smg1 becomes essential for NMD when Smg5 function is partially compromised.\",\n      \"method\": \"Drosophila genetics, NMD reporter assays, epistasis analysis\",\n      \"journal\": \"Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with defined NMD phenotypic readouts in Drosophila, single lab\",\n      \"pmids\": [\"29903866\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"In C. elegans, the PIN domain of SMG-5, though catalytically inactive by canonical criteria, contains highly conserved residues essential for NMD. AlphaFold predicts a direct PIN-PIN interaction between SMG-5 and SMG-6, validated by in vitro pulldowns. Compensatory salt-bridge flip mutations confirm this interface is functionally required for SMG-6-mediated mRNA cleavage.\",\n      \"method\": \"AlphaFold structural prediction, in vitro pulldown, C. elegans genetic complementary mutagenesis, NMD reporter assays\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro pulldown plus in vivo compensatory mutagenesis, single lab, structural prediction not experimentally solved\",\n      \"pmids\": [\"41638882\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"AlphaFold models predict a high-confidence SMG5-SMG6 PIN domain interface forming a composite active site, where a conserved SMG5 aspartate (D893) completes the canonical tetrad required for PIN-domain catalysis. In vitro, SMG6 alone has weak endonuclease activity that is enhanced ~10-fold by the addition of the SMG5 PIN domain. Mutations at the predicted interface, RNA-binding sites, or active site abolish this composite endonuclease activity and impair cellular NMD.\",\n      \"method\": \"AlphaFold structural prediction, in vitro reconstituted endonuclease assay, mutagenesis, cell-based NMD assay\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro biochemical reconstitution plus mutagenesis plus cellular NMD assay, single lab, structure predicted not experimentally solved\",\n      \"pmids\": [\"41763597\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"SMG5 and SMG6 interact via their PIN domains to form a composite PIN (cPIN) heterodimer with full endonuclease activity. Reconstituted SMG5-SMG6 cPIN heterodimers show high in vitro activity; SMG5 completes the SMG6 active site and substrate binding site. Mutations at their predicted interaction surfaces, RNA-binding sites, or active site attenuate or abolish cPIN activity in vitro and impair cellular NMD.\",\n      \"method\": \"Structural predictions (AlphaFold), biochemical in vitro reconstitution, mutagenesis, cell-based NMD analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution plus mutagenesis plus cellular NMD assay, converges with two independent studies (PMIDs 41638882, 41763597) published concurrently\",\n      \"pmids\": [\"41714610\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Conditional knockout of Smg5 in mouse craniofacial neural crest cells causes abnormal accumulation of a PTC-containing Porcn transcript, leading to reduced Porcn protein and impaired Wnt5a/JNK signaling, resulting in hypoplastic mandibles, tongue mispositioning, and cleft palate. Wnt5a addition to SMG5-deficient CNC explants ameliorates cell death.\",\n      \"method\": \"Conditional knockout mouse model, transcriptome analysis, Western blot for Porcn, Wnt5a rescue in CNC explants\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with mechanistic pathway placement via Porcn/Wnt5a, single lab, partially relies on transcriptome correlation for Porcn mechanism\",\n      \"pmids\": [\"40071146\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SMG5 knockout in mouse embryonic germ cells causes spermatogenesis failure (Sertoli cell-only phenotype) due to defective spermatogonial differentiation and maintenance. SMG5 loss leads to hyperactivation of the p38 MAPK signaling pathway causing widespread cell death during spermatogonial differentiation.\",\n      \"method\": \"Conditional knockout mouse model, transcriptome analysis, Western blot for p38 MAPK pathway components, histology\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with defined cellular and molecular phenotype and pathway placement, single lab\",\n      \"pmids\": [\"39704269\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Smg5 knockout mESCs are viable but show delayed differentiation. SMG5 loss causes upregulation of c-MYC protein (but not c-Myc mRNA), attributed to enhanced protein synthesis, and dysregulates alternative splicing of stem cell differentiation regulators.\",\n      \"method\": \"Conditional knockout mESCs, Western blot, polysome profiling inference, transcriptome/alternative splicing analysis\",\n      \"journal\": \"Biomolecules\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO with defined molecular phenotype, single lab; mechanistic basis of c-MYC upregulation inferred rather than directly tested\",\n      \"pmids\": [\"39199410\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Conditional knockout of Smg5 in oligodendrocyte lineage cells impairs oligodendrocyte differentiation and myelination due to failure to degrade PTC-containing Hnrnpl variant transcripts. Excess HNRNPL disrupts alternative splicing of myelin-associated genes Mag and Nfasc.\",\n      \"method\": \"Conditional knockout mouse model, RNA analysis, Western blot, electron microscopy of myelin, motor function assays\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with defined NMD substrate (Hnrnpl), downstream splicing mechanism identified, single lab\",\n      \"pmids\": [\"40930975\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SMG5 is a catalytically inactive PIN-domain and 14-3-3-like domain-containing NMD factor that functions primarily as a scaffold: its 14-3-3-like domain heterodimerizes with SMG7 to recognize phosphorylated UPF1 (at C-terminal SQ motifs) and recruit PP2A for UPF1 dephosphorylation, while its PIN domain directly interacts with the SMG6 PIN domain to complete a composite active site that licenses and enhances SMG6 endonuclease activity ~10-fold, thereby coupling UPF1 phosphorylation to downstream mRNA cleavage.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SMG5 is a core nonsense-mediated mRNA decay (NMD) factor that couples phosphorylation of the central NMD helicase UPF1 to downstream mRNA destruction [#1, #7]. Although its PIN domain lacks the canonical catalytic residues for RNase H-type nuclease activity, SMG5 itself has no intrinsic endonuclease function [#0]. Instead, it acts as a bifunctional scaffold. Through its 14-3-3-like domain it heterodimerizes back-to-back with SMG7, and this heterodimer recognizes the C-terminal phosphorylated Ser-Gln motifs of UPF1 in a phospho-dependent manner [#3, #4]; SMG5 recruits protein phosphatase 2A to dephosphorylate UPF1, thereby resetting the UPF1 phosphorylation cycle [#1, #2]. The SMG5-SMG7 module additionally licenses the endonucleolytic branch of NMD, since loss of this pathway inactivates SMG6-mediated cleavage and either SMG5 or SMG7 alone suffices to authorize SMG6 endonucleolysis [#7]. SMG5 further contributes directly to cleavage through its catalytically dead PIN domain, which docks onto the SMG6 PIN domain to form a composite active site in which a conserved SMG5 aspartate completes the catalytic tetrad, enhancing SMG6 endonuclease activity ~10-fold [#10, #11]. In vivo, SMG5-dependent NMD is essential for clearing PTC-containing transcripts; conditional loss in mouse tissues stabilizes specific substrates and disrupts development, including a Porcn/Wnt5a axis required for craniofacial morphogenesis [#12] and an Hnrnpl-dependent splicing program required for oligodendrocyte myelination [#15].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Established SMG5's first defined molecular role: linking the NMD machinery to UPF1 dephosphorylation rather than acting as an autonomous enzyme.\",\n      \"evidence\": \"Co-purification/IP and phosphatase assays in human cells, replicated by yeast two-hybrid and IP in C. elegans\",\n      \"pmids\": [\"12554878\", \"12554664\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not determine whether PP2A recruitment is direct or scaffolded through SMG7\", \"Structural basis of phospho-UPF1 recognition unresolved\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Resolved why SMG5 is not a nuclease: its PIN domain lacks the acidic catalytic triad present in the active SMG6 PIN domain, defining SMG5 as a non-catalytic NMD factor.\",\n      \"evidence\": \"X-ray crystallography of human SMG5/SMG6 PIN domains with in vitro ssRNA assays and Drosophila dominant-negative genetics\",\n      \"pmids\": [\"17053788\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address whether the SMG5 PIN domain has any function despite lacking catalysis\", \"No interaction tested between SMG5 and SMG6 PIN domains\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Defined the structural logic of the SMG5-SMG7 module, showing 14-3-3-like heterodimerization is required for high-affinity phospho-UPF1 binding and for NMD.\",\n      \"evidence\": \"Crystal structure of C. elegans SMG5-SMG7 plus structure-based mutagenesis and human cell NMD reporters\",\n      \"pmids\": [\"23348841\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Degradative activity localized to SMG7, leaving SMG5's contribution to decay undefined\", \"Did not address SMG6 branch coupling\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Reconstituted phospho-dependent UPF1 recognition by purified SMG5-SMG7, distinguishing it from SMG6's largely phospho-independent UPF1 binding.\",\n      \"evidence\": \"In vitro reconstitution with purified proteins, crystallography of the SMG6 14-3-3-like domain, and binding assays\",\n      \"pmids\": [\"25013172\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not test functional consequences of the two recognition modes in cells\", \"Did not address how SMG5-SMG7 and SMG6 binding are coordinated on UPF1\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Proposed that SMG5 bridges phospho-UPF1 to decapping via PNRC2 and Dcp1a, placing SMG5 at a specific decay step.\",\n      \"evidence\": \"Co-IP, siRNA knockdown, tethering and microarray in a single lab\",\n      \"pmids\": [\"23234702\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Directly contradicted by a later study finding no SMG5-PNRC2 interaction\", \"Single-lab interaction not independently reproduced\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Challenged the SMG5-PNRC2 bridging model, reassigning PNRC2-driven 5'-3' decay to a direct UPF1-PNRC2 interaction while confirming the SMG5-SMG7 requirement.\",\n      \"evidence\": \"Co-IP, tethering, siRNA knockdown and NMD reporters\",\n      \"pmids\": [\"29348139\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Discrepancy with the earlier PNRC2 study not mechanistically resolved\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrated genetic essentiality of Smg5 for NMD in vivo, covering both SMG6-dependent and SMG6-independent decay routes.\",\n      \"evidence\": \"Drosophila genetics, NMD reporters and epistasis analysis\",\n      \"pmids\": [\"29903866\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular identity of the SMG6-independent route not defined\", \"Epistasis with Smg1 not extended to mammalian systems\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Established that the SMG5-SMG7 pathway licenses the SMG6 endonucleolytic branch, with SMG5 able to substitute for SMG7.\",\n      \"evidence\": \"siRNA depletion of SMG5/SMG7 with transcriptome-wide RNA-seq and NMD reporters in human cells\",\n      \"pmids\": [\"34172724\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the physical basis of SMG6 licensing by SMG5\", \"Did not determine redundancy mechanism between SMG5 and SMG7\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Revealed the molecular basis of SMG6 licensing: the catalytically dead SMG5 PIN domain directly contacts the SMG6 PIN domain to form a composite active site that completes the catalytic tetrad and enhances cleavage ~10-fold.\",\n      \"evidence\": \"AlphaFold modeling, in vitro pulldowns and reconstituted endonuclease assays, compensatory mutagenesis and cellular NMD assays across C. elegans and human components, converging across three concurrent studies\",\n      \"pmids\": [\"41638882\", \"41763597\", \"41714610\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Composite PIN interface predicted by AlphaFold but not experimentally solved by crystallography or cryo-EM\", \"Stoichiometry and regulation of cPIN assembly in cells undefined\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Connected SMG5-dependent NMD to mammalian developmental programs by identifying tissue-specific PTC-containing substrates whose stabilization drives phenotypes.\",\n      \"evidence\": \"Conditional knockout mice in neural crest and oligodendrocyte lineages with transcriptome analysis, Western blot, rescue and histology (Porcn/Wnt5a; Hnrnpl/Mag/Nfasc)\",\n      \"pmids\": [\"40071146\", \"40930975\", \"39704269\", \"39199410\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Some substrate-to-phenotype links rely on transcriptome correlation\", \"c-MYC and p38 MAPK effects mechanistically inferred rather than fully reconstituted\", \"Single-lab tissue models\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How phospho-UPF1 recognition by the SMG5-SMG7 14-3-3 module, PP2A recruitment, and assembly of the SMG5-SMG6 composite PIN are temporally coordinated on a single mRNP remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No integrated structure of UPF1-SMG5-SMG6/SMG7 on substrate\", \"Order of dephosphorylation versus endonucleolytic licensing unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [3, 7, 11]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [10, 11]},\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [4, 10]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [1, 7, 11]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"complexes\": [\"SMG5-SMG7 14-3-3-like heterodimer\", \"SMG5-SMG6 composite PIN (cPIN) heterodimer\"],\n    \"partners\": [\"SMG7\", \"SMG6\", \"UPF1\", \"PP2A\", \"UPF2\", \"UPF3X\", \"SMG1\", \"PNRC2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}