{"gene":"EXOSC7","run_date":"2026-04-28T17:46:03","timeline":{"discoveries":[{"year":2001,"finding":"EXOSC7 (human Rrp42) was identified as a subunit of the human RNA exosome complex, purified by mass spectrometry. The human exosome was shown to be required for rapid degradation of AU-rich element (ARE)-containing mRNAs in a cell-free system, and this activity required recruitment by ARE-binding proteins such as KSRP.","method":"Mass spectrometry purification of human exosome complex; cell-free ARE-mRNA decay assay with immunodepletion","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1–2 — biochemical purification, reconstituted cell-free decay assay, replicated by subsequent studies","pmids":["11719186"],"is_preprint":false},{"year":2006,"finding":"EXOSC7 (human Rrp42) is a structural subunit of the nine-subunit human exosome core. Reconstitution of the 9-subunit human exosome and X-ray crystallography at 3.35 Å revealed that the human exosome core forms a ring-like architecture with EXOSC7 contributing to the barrel structure. Biochemical analysis showed that purified human Rrp41/Rrp45 (but not the isolated ring including EXOSC7) exhibit processive phosphorolytic activity, and the 9-subunit human exosome as a whole displays processive phosphorolytic activity on AU-rich and polyadenylated RNA substrates.","method":"In vitro reconstitution of 9-subunit human exosome from purified recombinant subunits; X-ray crystallography (3.35 Å); exoribonuclease activity assays with multiple RNA substrates","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 — crystal structure plus in vitro reconstitution and enzymatic assays with mutagenesis in single rigorous study","pmids":["17174896"],"is_preprint":false},{"year":2004,"finding":"Yeast two-hybrid analysis of human mRNA decay proteins revealed that EXOSC7 (Rrp42) participates in internal protein-protein interactions within the exosome complex, and the interaction network predicted the internal organization of the exosome barrel, placing EXOSC7 in contact with adjacent ring subunits.","method":"Yeast two-hybrid protein interaction mapping of 38 human mRNA decay proteins","journal":"Genome research","confidence":"Medium","confidence_rationale":"Tier 3 — yeast two-hybrid, single method, but interactions subsequently validated by structural studies","pmids":["15231747"],"is_preprint":false},{"year":2010,"finding":"The human nine-subunit exosome core (which includes EXOSC7) was shown to be catalytically inert and to serve a structural/scaffold function. The core associates with two distinct processive RNases, hDIS3 (predominantly nuclear) and hDIS3L (strictly cytoplasmic), establishing that the core complex serves as a platform for differentially localized ribonucleases.","method":"Co-immunoprecipitation, subcellular fractionation, reciprocal pulldowns, RNase activity assays, immunofluorescence microscopy in human cells","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (Co-IP, fractionation, activity assays, imaging) in single study, replicated by structural work","pmids":["20531386"],"is_preprint":false},{"year":2011,"finding":"The RNA exosome core complex (containing EXOSC7 as a structural subunit) associates with AID (activation-induced cytidine deaminase) in B lymphocytes activated for class switch recombination, accumulates on immunoglobulin heavy-chain switch regions in an AID-dependent manner, and is required for optimal class switch recombination. A recombinant exosome core complex imparts robust AID- and transcription-dependent DNA deamination of both strands of transcribed substrates in vitro, revealing a role for the structural exosome core in directing AID to template DNA strands.","method":"Co-immunoprecipitation, ChIP in activated B cells, in vitro transcription-coupled DNA deamination assay with recombinant exosome core, genetic knockdown (CSR assay)","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro reconstitution with recombinant exosome core plus genetic and ChIP validation, multiple orthogonal methods","pmids":["21255825"],"is_preprint":false},{"year":2011,"finding":"The RNA exosome (containing EXOSC7) is recruited by zinc-finger antiviral protein (ZAP) via cofactor RNA helicase p72 to degrade multiply spliced HIV-1 mRNAs from the 3' end. Depletion of exosome subunits reduced ZAP's antiviral activity, placing the exosome downstream of ZAP in a pathway that selectively degrades specific viral transcripts.","method":"siRNA knockdown of exosome subunits, co-immunoprecipitation of ZAP with exosome, HIV-1 infection assays with viral RNA quantification","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2–3 — genetic epistasis by knockdown with specific viral RNA phenotype, Co-IP; EXOSC7 not individually distinguished from other core subunits","pmids":["21876179"],"is_preprint":false},{"year":2014,"finding":"Crystal structure of the ten-subunit RNA exosome (Exo9 core plus Rrp6) at 3.3 Å from S. cerevisiae (ortholog of human complex containing EXOSC7/Rrp42) revealed that the S1/KH ring formed by cap subunits sits atop the barrel ring (which includes Rrp42/EXOSC7), and that the integrity of this S1/KH ring is required for directing RNA substrates to Rrp6. Solution studies with human exosome complexes confirmed the conserved RNA path to Rrp6 is dependent on S1/KH ring integrity.","method":"X-ray crystallography (3.3 Å), solution RNA-binding assays with human and yeast exosome complexes, mutational analysis","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure with human complex validation and mutagenesis","pmids":["25043052"],"is_preprint":false},{"year":2025,"finding":"Using an inducible dual-guide CRISPR/Cas9 system in mouse embryonic stem cells, EXOSC7 (Exosc7) was shown to be one of three subunits (together with Exosc2 and Exosc4) that initiate RNA exosome complex formation, acting as early nucleators in a sequential hierarchical assembly pathway. Barrel and cap subunits are incorporated after this initial nucleation step. Orphan exosome subunits (those not incorporated into the complex) are selectively degraded via the ubiquitin-proteasome system, establishing a quality control mechanism for exosome biogenesis.","method":"Inducible CRISPR/Cas9 knockout of individual exosome subunits in mESCs; quantitative mass spectrometry to assess complex composition; proteasome inhibition experiments","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 — systematic genetic perturbation with quantitative proteomics, EXOSC7 specifically identified as assembly initiator; preprint, not yet peer-reviewed","pmids":["bio_10.1101_2025.03.14.643291"],"is_preprint":true}],"current_model":"EXOSC7 (Rrp42) is a structural subunit of the catalytically inert nine-subunit human RNA exosome core, where it contributes to the barrel architecture that scaffolds processive ribonucleases (hDIS3 in the nucleus, hDIS3L in the cytoplasm) and Rrp6; it is one of three subunits (with EXOSC2 and EXOSC4) that nucleate exosome assembly in a hierarchical pathway, with unincorporated orphan subunits degraded by the ubiquitin-proteasome system, and the intact core complex participates in ARE-mRNA decay, antiviral RNA degradation, and AID-directed DNA deamination for antibody class switch recombination."},"narrative":{"teleology":[{"year":2001,"claim":"Identification of EXOSC7 as a subunit of the human RNA exosome and demonstration that the complex is required for ARE-mRNA decay established the gene's involvement in regulated mRNA turnover.","evidence":"Mass spectrometry purification of the human exosome; cell-free ARE-mRNA decay assay with immunodepletion","pmids":["11719186"],"confidence":"High","gaps":["Whether EXOSC7 contributes catalytic activity or is purely structural was unresolved","Stoichiometry and architecture of the human exosome were unknown"]},{"year":2004,"claim":"Yeast two-hybrid mapping of intra-exosome contacts placed EXOSC7 adjacent to specific ring subunits, providing the first prediction of the internal organization of the barrel.","evidence":"Yeast two-hybrid interaction mapping among 38 human mRNA decay proteins","pmids":["15231747"],"confidence":"Medium","gaps":["Binary yeast two-hybrid contacts lacked structural validation at atomic resolution","Direct versus bridged interactions could not be distinguished"]},{"year":2006,"claim":"Reconstitution and X-ray crystallography of the nine-subunit human exosome at 3.35 Å resolved EXOSC7's position in the barrel ring and showed that the full core displays processive phosphorolytic activity, directly answering the question of subunit architecture.","evidence":"Recombinant reconstitution of nine-subunit human exosome; X-ray crystallography (3.35 Å); exoribonuclease activity assays","pmids":["17174896"],"confidence":"High","gaps":["Whether the in vivo exosome core retains catalytic activity or is inert awaited resolution","Association with processive catalytic subunits (Dis3 family) was not yet characterized in human cells"]},{"year":2010,"claim":"Demonstration that the human exosome core is catalytically inert and serves as a scaffold for compartment-specific ribonucleases (hDIS3 nuclear, hDIS3L cytoplasmic) redefined EXOSC7's role as purely structural.","evidence":"Co-immunoprecipitation, subcellular fractionation, RNase activity assays, immunofluorescence in human cells","pmids":["20531386"],"confidence":"High","gaps":["How RNA is channeled through the barrel to the catalytic subunits remained structurally unclear","Contribution of individual barrel subunits to substrate specificity was unknown"]},{"year":2011,"claim":"Two studies expanded the functional repertoire of the exosome core beyond mRNA decay: the core was shown to associate with AID to direct DNA deamination on both strands during class switch recombination, and to mediate ZAP-directed degradation of HIV-1 transcripts.","evidence":"ChIP, co-immunoprecipitation in activated B cells, in vitro transcription-coupled DNA deamination assay with recombinant exosome core (CSR study); siRNA knockdown of exosome subunits with HIV-1 infection assays (ZAP study)","pmids":["21255825","21876179"],"confidence":"High","gaps":["Whether EXOSC7 specifically contacts AID or is engaged indirectly through other core subunits was not determined","The mechanism by which the structural core promotes strand-specific AID activity is incompletely understood","EXOSC7 was not individually distinguished from other core subunits in the ZAP-mediated antiviral pathway"]},{"year":2014,"claim":"A 3.3 Å crystal structure of the ten-subunit exosome (Exo9 + Rrp6) revealed the RNA channeling path through the barrel and showed that cap-ring integrity is required for directing substrates to Rrp6, clarifying how the barrel scaffold including EXOSC7 organizes RNA processing.","evidence":"X-ray crystallography (3.3 Å, yeast) with validation using human exosome complexes in solution RNA-binding assays and mutagenesis","pmids":["25043052"],"confidence":"High","gaps":["Individual contributions of barrel subunits (including EXOSC7) to RNA threading were not dissected","Structural basis for how the exosome core directs AID activity was not addressed"]},{"year":2025,"claim":"Systematic CRISPR knockout revealed that EXOSC7, together with EXOSC2 and EXOSC4, acts as an early nucleator of hierarchical exosome assembly, with orphan subunits degraded by the ubiquitin–proteasome system — establishing a quality-control pathway for exosome biogenesis.","evidence":"Inducible CRISPR/Cas9 knockout of individual exosome subunits in mESCs; quantitative mass spectrometry; proteasome inhibition (preprint)","pmids":["bio_10.1101_2025.03.14.643291"],"confidence":"Medium","gaps":["Preprint awaiting peer review","Whether the nucleation hierarchy is conserved in differentiated human cell types is untested","The E3 ligase(s) responsible for ubiquitination of orphan subunits were not identified"]},{"year":null,"claim":"It remains unresolved how the structural barrel, and EXOSC7 specifically, contributes to substrate selectivity among diverse RNA and DNA substrates processed by the exosome, and whether EXOSC7 mutations cause human disease.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structure of a human exosome–AID complex exists","No disease-causing mutations in EXOSC7 have been reported","Individual contribution of EXOSC7 versus other barrel subunits to RNA threading specificity is unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[0,1,6]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[1,3,6]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[3,4]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[3]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[0,1,3,5,6]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[4,5]}],"complexes":["RNA exosome core (Exo-9)","RNA exosome (Exo-10, with Rrp6)","RNA exosome (Exo-10, with DIS3/DIS3L)"],"partners":["EXOSC2","EXOSC4","DIS3","DIS3L","EXOSC10","AICDA","ZC3HAV1"],"other_free_text":[]},"mechanistic_narrative":"EXOSC7 (Rrp42) is a structural subunit of the nine-subunit human RNA exosome core, where it contributes to the barrel architecture that scaffolds processive ribonucleases in both the nucleus and cytoplasm. X-ray crystallography of the reconstituted human exosome core at 3.35 Å demonstrated that EXOSC7 is integrated into the hexameric ring, and the assembled nine-subunit core is catalytically inert, instead serving as a platform for the processive RNases hDIS3 (nuclear) and hDIS3L (cytoplasmic) [PMID:17174896, PMID:20531386]. Through this scaffolding role the exosome core participates in AU-rich element (ARE)-mediated mRNA decay, ZAP-directed degradation of HIV-1 transcripts, and AID-dependent DNA deamination on immunoglobulin switch regions during class switch recombination [PMID:11719186, PMID:21876179, PMID:21255825]. EXOSC7 is one of three subunits (with EXOSC2 and EXOSC4) that nucleate hierarchical exosome assembly, with orphan unincorporated subunits cleared by the ubiquitin–proteasome system [PMID:bio_10.1101_2025.03.14.643291]."},"prefetch_data":{"uniprot":{"accession":"Q15024","full_name":"Exosome complex component RRP42","aliases":["Exosome component 7","Ribosomal RNA-processing protein 42","p8"],"length_aa":291,"mass_kda":31.8,"function":"Non-catalytic component of the RNA exosome complex which has 3'->5' exoribonuclease activity and participates in a multitude of cellular RNA processing and degradation events. In the nucleus, the RNA exosome complex is involved in proper maturation of stable RNA species such as rRNA, snRNA and snoRNA, in the elimination of RNA processing by-products and non-coding 'pervasive' transcripts, such as antisense RNA species and promoter-upstream transcripts (PROMPTs), and of mRNAs with processing defects, thereby limiting or excluding their export to the cytoplasm. The RNA exosome may be involved in Ig class switch recombination (CSR) and/or Ig variable region somatic hypermutation (SHM) by targeting AICDA deamination activity to transcribed dsDNA substrates. In the cytoplasm, the RNA exosome complex is involved in general mRNA turnover and specifically degrades inherently unstable mRNAs containing AU-rich elements (AREs) within their 3' untranslated regions, and in RNA surveillance pathways, preventing translation of aberrant mRNAs. It seems to be involved in degradation of histone mRNA. The catalytic inactive RNA exosome core complex of 9 subunits (Exo-9) is proposed to play a pivotal role in the binding and presentation of RNA for ribonucleolysis, and to serve as a scaffold for the association with catalytic subunits and accessory proteins or complexes","subcellular_location":"Nucleus, nucleolus; Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/Q15024/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/EXOSC7","classification":"Common Essential","n_dependent_lines":1135,"n_total_lines":1208,"dependency_fraction":0.9395695364238411},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"DRG1","stoichiometry":0.2},{"gene":"PSPC1","stoichiometry":0.2},{"gene":"RACK1","stoichiometry":0.2},{"gene":"RBM7","stoichiometry":0.2},{"gene":"RPS16","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/EXOSC7","total_profiled":1310},"omim":[{"mim_id":"606488","title":"EXOSOME COMPONENT 7; EXOSC7","url":"https://www.omim.org/entry/606488"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nuclear speckles","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/EXOSC7"},"hgnc":{"alias_symbol":["hRrp42p","Rrp42p","RRP42","EAP1","KIAA0116","p8"],"prev_symbol":[]},"alphafold":{"accession":"Q15024","domains":[{"cath_id":"3.30.230.70","chopping":"8-280","consensus_level":"medium","plddt":85.5814,"start":8,"end":280}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q15024","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q15024-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q15024-F1-predicted_aligned_error_v6.png","plddt_mean":84.25},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=EXOSC7","jax_strain_url":"https://www.jax.org/strain/search?query=EXOSC7"},"sequence":{"accession":"Q15024","fasta_url":"https://rest.uniprot.org/uniprotkb/Q15024.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q15024/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q15024"}},"corpus_meta":[{"pmid":"10698492","id":"PMC_10698492","title":"EAP1/Daxx 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of America","url":"https://pubmed.ncbi.nlm.nih.gov/21876179","citation_count":246,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"20531386","id":"PMC_20531386","title":"The human core exosome interacts with differentially localized processive RNases: hDIS3 and hDIS3L.","date":"2010","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/20531386","citation_count":224,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"27173435","id":"PMC_27173435","title":"An organelle-specific protein landscape identifies novel diseases and molecular mechanisms.","date":"2016","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/27173435","citation_count":211,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"24332808","id":"PMC_24332808","title":"PRP19 transforms into a sensor of RPA-ssDNA after DNA damage and drives ATR activation via a ubiquitin-mediated circuitry.","date":"2013","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/24332808","citation_count":204,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"32807901","id":"PMC_32807901","title":"UFMylation maintains tumour suppressor p53 stability by antagonizing its ubiquitination.","date":"2020","source":"Nature cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/32807901","citation_count":168,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"11849973","id":"PMC_11849973","title":"The yin and yang of the exosome.","date":"2002","source":"Trends in cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/11849973","citation_count":150,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"21832049","id":"PMC_21832049","title":"Interactions of pathological hallmark proteins: tubulin polymerization promoting protein/p25, beta-amyloid, and alpha-synuclein.","date":"2011","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/21832049","citation_count":131,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"25043052","id":"PMC_25043052","title":"Structure of an Rrp6-RNA exosome complex bound to poly(A) RNA.","date":"2014","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/25043052","citation_count":126,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"15231747","id":"PMC_15231747","title":"A protein interaction framework for human mRNA degradation.","date":"2004","source":"Genome research","url":"https://pubmed.ncbi.nlm.nih.gov/15231747","citation_count":123,"is_preprint":false,"source_track":"gene2pubmed"}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":9502,"output_tokens":525,"usd":0.01819},"stage2":{"model":"claude-opus-4-6","input_tokens":3689,"output_tokens":963,"usd":0.06378},"total_usd":0.27169,"stage1_batch_id":"msgbatch_0118RScg3WGaGkaZRtWZbtce","stage2_batch_id":"msgbatch_01Cpfzvtbj42aqp5oYZ5Te2s","note":"batch pricing = 50% of standard","round2_stage1":{"model":"claude-sonnet-4-6","input_tokens":21360,"output_tokens":3316,"usd":0.05691},"round2_rules_fired":"R3","round2_stage2":{"model":"claude-opus-4-6","input_tokens":5888,"output_tokens":2364,"usd":0.13281}},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2025,\n      \"finding\": \"EXOSC7 (Exosc7) is one of three subunits (along with Exosc2 and Exosc4) that initiate RNA exosome complex formation, acting early in a sequential assembly pathway that facilitates subsequent incorporation of barrel and cap subunits in a defined hierarchy.\",\n      \"method\": \"Inducible dual-guide CRISPR/Cas9 knockout system in mouse embryonic stem cells with systematic dissection of assembly order\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic genetic dissection with defined cellular phenotypes, single preprint not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.03.14.643291\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Orphan EXOSC7 subunits (when not incorporated into the exosome complex) are selectively degraded via the ubiquitin-proteasome system, enforcing quality control over RNA exosome biogenesis.\",\n      \"method\": \"Inducible dual-guide CRISPR/Cas9 knockout in mouse embryonic stem cells with proteasome inhibition and protein abundance measurements\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — defined degradation pathway in a clean genetic system, single preprint\",\n      \"pmids\": [\"bio_10.1101_2025.03.14.643291\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"EXOSC7 is an early-assembly initiator subunit of the RNA exosome complex that, together with EXOSC2 and EXOSC4, nucleates sequential incorporation of barrel and cap subunits; unincorporated EXOSC7 is degraded by the ubiquitin-proteasome system as part of exosome biogenesis quality control.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll classify each paper first, then extract discoveries only from KEEP papers.\n\n**Classification:**\n\nPapers 1-12 in the retrieved corpus (EAP1 = Enhanced At Puberty 1, a transcriptional regulator / Daxx-interacting protein / Candida albicans adhesin / fungal protease): These are all ALIAS COLLISION papers — \"EAP1\" here refers to completely different proteins (hypothalamic transcription factor, yeast/fungal proteins, Candida albicans adhesin, Sporisorium protease). EXCLUDE all.\n\nPaper 13 (RRP42/Arabidopsis exosome): Plant gene, SYMBOL COLLISION. EXCLUDE.\n\nPaper 14-15 (Sporisorium EAP1 protease): ALIAS COLLISION. EXCLUDE.\n\nPaper 16 (Preprint - hierarchical assembly of mammalian RNA exosome, mentions Exosc7): KEEP — directly describes EXOSC7's role in exosome assembly.\n\n**Gene2pubmed curated papers:**\n\n- PMID 16189514, 12477932, 28514442, 26496610, 25416956, 15635413, 32296183, 11790298, 14702039, 21873635, 29395067, 15489334, 35271311, 26344197, 26949251, 32807901, 21832049: Large interactome/proteome studies or unrelated studies — these detect EXOSC7 as part of exosome complex interactions but provide no direct mechanistic findings specific to EXOSC7. These are interactome datasets, cDNA collections, or unrelated biology. EXCLUDE from Discovery extraction (no EXOSC7-specific mechanism).\n\n- PMID 11719186 (Chen et al., Cell 2001 — AU binding proteins recruit exosome): KEEP — describes human exosome characterization including EXOSC7 as a subunit.\n\n- PMID 17174896 (Liu et al., Cell 2006 — Reconstitution, activities, structure of eukaryotic RNA exosome): KEEP — directly characterizes human exosome structure including EXOSC7 (Rrp42 equivalent).\n\n- PMID 11849973 (Butler 2002 — yin and yang of exosome): Review, no direct experiments on EXOSC7. EXCLUDE.\n\n- PMID 25043052 (Wasmuth et al., Nature 2014 — Rrp6-RNA exosome structure): KEEP — structural study of exosome relevant to EXOSC7.\n\n- PMID 21255825 (Basu et al., Cell 2011 — RNA exosome targets AID): KEEP — functional characterization of exosome core.\n\n- PMID 20531386 (Tomecki et al., EMBO J 2010 — human core exosome): KEEP — characterizes human exosome core.\n\n- PMID 21876179 (Zhu et al., PNAS 2011 — ZAP recruits RNA exosome): KEEP — exosome recruited for HIV-1 mRNA degradation.\n\n- PMID 15231747 (Lehner & Sanderson 2004 — protein interaction framework for mRNA degradation): KEEP — yeast two-hybrid interactions of exosome subunits.\n\n- PMID 22939629, 26186194, 33961781: BioPlex/interactome datasets — detect EXOSC7 interactions but no EXOSC7-specific mechanism. EXCLUDE.\n\n- PMID 24332808 (PRP19/ATR): Unrelated. EXCLUDE.\n\n- PMID 32807901 (UFMylation/p53): Unrelated. EXCLUDE.\n\n- PMID 21832049 (TPPP/p25): Unrelated. EXCLUDE.\n\n- PMID 27173435 (ciliary proteins): Unrelated. EXCLUDE.\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2001,\n      \"finding\": \"EXOSC7 (human Rrp42) was identified as a subunit of the human RNA exosome complex, purified by mass spectrometry. The human exosome was shown to be required for rapid degradation of AU-rich element (ARE)-containing mRNAs in a cell-free system, and this activity required recruitment by ARE-binding proteins such as KSRP.\",\n      \"method\": \"Mass spectrometry purification of human exosome complex; cell-free ARE-mRNA decay assay with immunodepletion\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — biochemical purification, reconstituted cell-free decay assay, replicated by subsequent studies\",\n      \"pmids\": [\"11719186\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"EXOSC7 (human Rrp42) is a structural subunit of the nine-subunit human exosome core. Reconstitution of the 9-subunit human exosome and X-ray crystallography at 3.35 Å revealed that the human exosome core forms a ring-like architecture with EXOSC7 contributing to the barrel structure. Biochemical analysis showed that purified human Rrp41/Rrp45 (but not the isolated ring including EXOSC7) exhibit processive phosphorolytic activity, and the 9-subunit human exosome as a whole displays processive phosphorolytic activity on AU-rich and polyadenylated RNA substrates.\",\n      \"method\": \"In vitro reconstitution of 9-subunit human exosome from purified recombinant subunits; X-ray crystallography (3.35 Å); exoribonuclease activity assays with multiple RNA substrates\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus in vitro reconstitution and enzymatic assays with mutagenesis in single rigorous study\",\n      \"pmids\": [\"17174896\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Yeast two-hybrid analysis of human mRNA decay proteins revealed that EXOSC7 (Rrp42) participates in internal protein-protein interactions within the exosome complex, and the interaction network predicted the internal organization of the exosome barrel, placing EXOSC7 in contact with adjacent ring subunits.\",\n      \"method\": \"Yeast two-hybrid protein interaction mapping of 38 human mRNA decay proteins\",\n      \"journal\": \"Genome research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — yeast two-hybrid, single method, but interactions subsequently validated by structural studies\",\n      \"pmids\": [\"15231747\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The human nine-subunit exosome core (which includes EXOSC7) was shown to be catalytically inert and to serve a structural/scaffold function. The core associates with two distinct processive RNases, hDIS3 (predominantly nuclear) and hDIS3L (strictly cytoplasmic), establishing that the core complex serves as a platform for differentially localized ribonucleases.\",\n      \"method\": \"Co-immunoprecipitation, subcellular fractionation, reciprocal pulldowns, RNase activity assays, immunofluorescence microscopy in human cells\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (Co-IP, fractionation, activity assays, imaging) in single study, replicated by structural work\",\n      \"pmids\": [\"20531386\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The RNA exosome core complex (containing EXOSC7 as a structural subunit) associates with AID (activation-induced cytidine deaminase) in B lymphocytes activated for class switch recombination, accumulates on immunoglobulin heavy-chain switch regions in an AID-dependent manner, and is required for optimal class switch recombination. A recombinant exosome core complex imparts robust AID- and transcription-dependent DNA deamination of both strands of transcribed substrates in vitro, revealing a role for the structural exosome core in directing AID to template DNA strands.\",\n      \"method\": \"Co-immunoprecipitation, ChIP in activated B cells, in vitro transcription-coupled DNA deamination assay with recombinant exosome core, genetic knockdown (CSR assay)\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro reconstitution with recombinant exosome core plus genetic and ChIP validation, multiple orthogonal methods\",\n      \"pmids\": [\"21255825\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The RNA exosome (containing EXOSC7) is recruited by zinc-finger antiviral protein (ZAP) via cofactor RNA helicase p72 to degrade multiply spliced HIV-1 mRNAs from the 3' end. Depletion of exosome subunits reduced ZAP's antiviral activity, placing the exosome downstream of ZAP in a pathway that selectively degrades specific viral transcripts.\",\n      \"method\": \"siRNA knockdown of exosome subunits, co-immunoprecipitation of ZAP with exosome, HIV-1 infection assays with viral RNA quantification\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — genetic epistasis by knockdown with specific viral RNA phenotype, Co-IP; EXOSC7 not individually distinguished from other core subunits\",\n      \"pmids\": [\"21876179\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Crystal structure of the ten-subunit RNA exosome (Exo9 core plus Rrp6) at 3.3 Å from S. cerevisiae (ortholog of human complex containing EXOSC7/Rrp42) revealed that the S1/KH ring formed by cap subunits sits atop the barrel ring (which includes Rrp42/EXOSC7), and that the integrity of this S1/KH ring is required for directing RNA substrates to Rrp6. Solution studies with human exosome complexes confirmed the conserved RNA path to Rrp6 is dependent on S1/KH ring integrity.\",\n      \"method\": \"X-ray crystallography (3.3 Å), solution RNA-binding assays with human and yeast exosome complexes, mutational analysis\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure with human complex validation and mutagenesis\",\n      \"pmids\": [\"25043052\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Using an inducible dual-guide CRISPR/Cas9 system in mouse embryonic stem cells, EXOSC7 (Exosc7) was shown to be one of three subunits (together with Exosc2 and Exosc4) that initiate RNA exosome complex formation, acting as early nucleators in a sequential hierarchical assembly pathway. Barrel and cap subunits are incorporated after this initial nucleation step. Orphan exosome subunits (those not incorporated into the complex) are selectively degraded via the ubiquitin-proteasome system, establishing a quality control mechanism for exosome biogenesis.\",\n      \"method\": \"Inducible CRISPR/Cas9 knockout of individual exosome subunits in mESCs; quantitative mass spectrometry to assess complex composition; proteasome inhibition experiments\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic genetic perturbation with quantitative proteomics, EXOSC7 specifically identified as assembly initiator; preprint, not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.03.14.643291\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"EXOSC7 (Rrp42) is a structural subunit of the catalytically inert nine-subunit human RNA exosome core, where it contributes to the barrel architecture that scaffolds processive ribonucleases (hDIS3 in the nucleus, hDIS3L in the cytoplasm) and Rrp6; it is one of three subunits (with EXOSC2 and EXOSC4) that nucleate exosome assembly in a hierarchical pathway, with unincorporated orphan subunits degraded by the ubiquitin-proteasome system, and the intact core complex participates in ARE-mRNA decay, antiviral RNA degradation, and AID-directed DNA deamination for antibody class switch recombination.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"EXOSC7 is a structural subunit of the RNA exosome complex that, together with EXOSC2 and EXOSC4, initiates exosome assembly by nucleating the sequential incorporation of barrel and cap subunits in a defined hierarchy [bio_10.1101_2025.03.14.643291]. Unincorporated (orphan) EXOSC7 is selectively degraded by the ubiquitin–proteasome system, providing a quality-control mechanism that ensures proper exosome biogenesis [bio_10.1101_2025.03.14.643291].\",\n  \"teleology\": [\n    {\n      \"year\": 2025,\n      \"claim\": \"It was unknown how the nine-subunit exosome barrel assembles; systematic subunit knockout revealed that EXOSC7, EXOSC2, and EXOSC4 form the earliest assembly nucleus, establishing a defined hierarchical pathway for exosome biogenesis.\",\n      \"evidence\": \"Inducible dual-guide CRISPR/Cas9 knockout of individual exosome subunits in mouse embryonic stem cells with systematic dissection of assembly order (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.03.14.643291\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Preprint not yet peer-reviewed; awaits independent confirmation\",\n        \"Direct physical contacts within the EXOSC7–EXOSC2–EXOSC4 initiator trimer have not been biochemically reconstituted\",\n        \"Whether the same assembly hierarchy operates in non-embryonic cell types is untested\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"The fate of unassembled exosome subunits was unknown; proteasome inhibition showed that orphan EXOSC7 is selectively degraded via the ubiquitin–proteasome system, revealing a quality-control mechanism for exosome biogenesis.\",\n      \"evidence\": \"Proteasome inhibition and protein abundance measurements in CRISPR-knockout mouse embryonic stem cells (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.03.14.643291\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Preprint not yet peer-reviewed; awaits independent replication\",\n        \"The E3 ubiquitin ligase responsible for EXOSC7 ubiquitination has not been identified\",\n        \"Whether degradation of orphan EXOSC7 is coupled to specific ubiquitin chain types is unknown\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The upstream signals and specific ubiquitin ligase machinery that target orphan EXOSC7 for proteasomal degradation remain unidentified, and whether EXOSC7's role as an assembly initiator is conserved across tissues and species has not been tested.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No E3 ligase or ubiquitin chain specificity identified for orphan EXOSC7 degradation\",\n        \"Assembly hierarchy not validated in human cells or primary tissues\",\n        \"No structural model of the early EXOSC7–EXOSC2–EXOSC4 assembly intermediate\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"complexes\": [\"RNA exosome\"],\n    \"partners\": [\"EXOSC2\", \"EXOSC4\"],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"EXOSC7 (Rrp42) is a structural subunit of the nine-subunit human RNA exosome core, where it contributes to the barrel architecture that scaffolds processive ribonucleases in both the nucleus and cytoplasm. X-ray crystallography of the reconstituted human exosome core at 3.35 Å demonstrated that EXOSC7 is integrated into the hexameric ring, and the assembled nine-subunit core is catalytically inert, instead serving as a platform for the processive RNases hDIS3 (nuclear) and hDIS3L (cytoplasmic) [PMID:17174896, PMID:20531386]. Through this scaffolding role the exosome core participates in AU-rich element (ARE)-mediated mRNA decay, ZAP-directed degradation of HIV-1 transcripts, and AID-dependent DNA deamination on immunoglobulin switch regions during class switch recombination [PMID:11719186, PMID:21876179, PMID:21255825]. EXOSC7 is one of three subunits (with EXOSC2 and EXOSC4) that nucleate hierarchical exosome assembly, with orphan unincorporated subunits cleared by the ubiquitin–proteasome system [PMID:bio_10.1101_2025.03.14.643291].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Identification of EXOSC7 as a subunit of the human RNA exosome and demonstration that the complex is required for ARE-mRNA decay established the gene's involvement in regulated mRNA turnover.\",\n      \"evidence\": \"Mass spectrometry purification of the human exosome; cell-free ARE-mRNA decay assay with immunodepletion\",\n      \"pmids\": [\"11719186\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether EXOSC7 contributes catalytic activity or is purely structural was unresolved\",\n        \"Stoichiometry and architecture of the human exosome were unknown\"\n      ]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Yeast two-hybrid mapping of intra-exosome contacts placed EXOSC7 adjacent to specific ring subunits, providing the first prediction of the internal organization of the barrel.\",\n      \"evidence\": \"Yeast two-hybrid interaction mapping among 38 human mRNA decay proteins\",\n      \"pmids\": [\"15231747\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Binary yeast two-hybrid contacts lacked structural validation at atomic resolution\",\n        \"Direct versus bridged interactions could not be distinguished\"\n      ]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Reconstitution and X-ray crystallography of the nine-subunit human exosome at 3.35 Å resolved EXOSC7's position in the barrel ring and showed that the full core displays processive phosphorolytic activity, directly answering the question of subunit architecture.\",\n      \"evidence\": \"Recombinant reconstitution of nine-subunit human exosome; X-ray crystallography (3.35 Å); exoribonuclease activity assays\",\n      \"pmids\": [\"17174896\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether the in vivo exosome core retains catalytic activity or is inert awaited resolution\",\n        \"Association with processive catalytic subunits (Dis3 family) was not yet characterized in human cells\"\n      ]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstration that the human exosome core is catalytically inert and serves as a scaffold for compartment-specific ribonucleases (hDIS3 nuclear, hDIS3L cytoplasmic) redefined EXOSC7's role as purely structural.\",\n      \"evidence\": \"Co-immunoprecipitation, subcellular fractionation, RNase activity assays, immunofluorescence in human cells\",\n      \"pmids\": [\"20531386\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"How RNA is channeled through the barrel to the catalytic subunits remained structurally unclear\",\n        \"Contribution of individual barrel subunits to substrate specificity was unknown\"\n      ]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Two studies expanded the functional repertoire of the exosome core beyond mRNA decay: the core was shown to associate with AID to direct DNA deamination on both strands during class switch recombination, and to mediate ZAP-directed degradation of HIV-1 transcripts.\",\n      \"evidence\": \"ChIP, co-immunoprecipitation in activated B cells, in vitro transcription-coupled DNA deamination assay with recombinant exosome core (CSR study); siRNA knockdown of exosome subunits with HIV-1 infection assays (ZAP study)\",\n      \"pmids\": [\"21255825\", \"21876179\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether EXOSC7 specifically contacts AID or is engaged indirectly through other core subunits was not determined\",\n        \"The mechanism by which the structural core promotes strand-specific AID activity is incompletely understood\",\n        \"EXOSC7 was not individually distinguished from other core subunits in the ZAP-mediated antiviral pathway\"\n      ]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"A 3.3 Å crystal structure of the ten-subunit exosome (Exo9 + Rrp6) revealed the RNA channeling path through the barrel and showed that cap-ring integrity is required for directing substrates to Rrp6, clarifying how the barrel scaffold including EXOSC7 organizes RNA processing.\",\n      \"evidence\": \"X-ray crystallography (3.3 Å, yeast) with validation using human exosome complexes in solution RNA-binding assays and mutagenesis\",\n      \"pmids\": [\"25043052\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Individual contributions of barrel subunits (including EXOSC7) to RNA threading were not dissected\",\n        \"Structural basis for how the exosome core directs AID activity was not addressed\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Systematic CRISPR knockout revealed that EXOSC7, together with EXOSC2 and EXOSC4, acts as an early nucleator of hierarchical exosome assembly, with orphan subunits degraded by the ubiquitin–proteasome system — establishing a quality-control pathway for exosome biogenesis.\",\n      \"evidence\": \"Inducible CRISPR/Cas9 knockout of individual exosome subunits in mESCs; quantitative mass spectrometry; proteasome inhibition (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.03.14.643291\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Preprint awaiting peer review\",\n        \"Whether the nucleation hierarchy is conserved in differentiated human cell types is untested\",\n        \"The E3 ligase(s) responsible for ubiquitination of orphan subunits were not identified\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how the structural barrel, and EXOSC7 specifically, contributes to substrate selectivity among diverse RNA and DNA substrates processed by the exosome, and whether EXOSC7 mutations cause human disease.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No structure of a human exosome–AID complex exists\",\n        \"No disease-causing mutations in EXOSC7 have been reported\",\n        \"Individual contribution of EXOSC7 versus other barrel subunits to RNA threading specificity is unknown\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [0, 1, 6]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [1, 3, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [3, 4]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [0, 1, 3, 5, 6]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [4, 5]}\n    ],\n    \"complexes\": [\n      \"RNA exosome core (Exo-9)\",\n      \"RNA exosome (Exo-10, with Rrp6)\",\n      \"RNA exosome (Exo-10, with DIS3/DIS3L)\"\n    ],\n    \"partners\": [\n      \"EXOSC2\",\n      \"EXOSC4\",\n      \"DIS3\",\n      \"DIS3L\",\n      \"EXOSC10\",\n      \"AICDA\",\n      \"ZC3HAV1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}