{"gene":"PSMA3","run_date":"2026-04-28T19:45:45","timeline":{"discoveries":[{"year":1995,"finding":"The PSMA3 (HC8) gene encoding the alpha-type subunit of the human 20S proteasome was isolated and characterized. Its promoter requires CAAT and TATA boxes (but not GC boxes) for activity, distinguishing it from other proteasomal subunit promoters. The HC8 gene was mapped to chromosome 14q23.","method":"Gene isolation, chloramphenicol acetyltransferase promoter assay, chromosomal mapping","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — direct promoter functional assay with deletion analysis in a single lab","pmids":["7857283"],"is_preprint":false},{"year":2003,"finding":"Human Aurora-B kinase physically interacts with PSMA3 (alpha7/HC8), a subunit of the 20S proteasome. Aurora-B protein levels increase when the proteasome is inhibited with ALLN, suggesting Aurora-B undergoes proteasome-dependent degradation mediated by its binding to PSMA3.","method":"Yeast two-hybrid screen, GST pull-down assay, co-immunoprecipitation, proteasome inhibitor (ALLN) treatment in HeLa cells","journal":"Molecular and cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 2/3 — reciprocal binding confirmed by pull-down and Co-IP plus pharmacological evidence; single lab","pmids":["14674694"],"is_preprint":false},{"year":2011,"finding":"Proteomic profiling of PSMA3-interacting proteins in both cytoplasm and nucleus revealed a large set of partners involved in mRNA metabolism and splicing. In vitro biochemical studies confirmed direct interactions between PSMA3 and splicing factors. Furthermore, the 20S proteasome was shown to regulate splicing of the SMN2 gene in vitro, establishing a functional link between the proteasome (via PSMA3) and mRNA processing.","method":"2D gel electrophoresis, tandem mass spectrometry (MS/MS), in vitro co-immunoprecipitation with splicing factors, in vitro splicing assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods (MS interactome + in vitro binding + functional splicing assay) in a single lab","pmids":["22079093"],"is_preprint":false},{"year":2019,"finding":"PSMA3-AS1 (an antisense lncRNA) forms an RNA duplex with pre-PSMA3 mRNA and promotes PSMA3 expression by increasing its mRNA stability, thereby upregulating 20S proteasome levels and conferring proteasome inhibitor resistance in multiple myeloma cells. Exosomal transfer of PSMA3 and PSMA3-AS1 from mesenchymal stem cells to myeloma cells mediates this resistance.","method":"Exosome characterization (DLS, TEM, Western blot), co-culture experiments, siRNA knockdown, xenograft mouse model, RNA duplex interaction assay","journal":"Clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2/3 — multiple methods including in vivo validation; mechanism of PSMA3 mRNA stabilization by lncRNA duplex is central finding relevant to PSMA3 protein expression","pmids":["30610101"],"is_preprint":false},{"year":2022,"finding":"The C-terminal 69-amino-acid region of PSMA3 (alpha7 subunit of the 20S proteasome) functions as an 'IDP trapper' that preferentially binds intrinsically disordered proteins (IDPs). A recombinant trapper fragment is sufficient to interact with multiple IDPs and competitively blocks their degradation by the 20S proteasome in vitro. Over one-third of PSMA3 trapper-binding proteins are known 20S proteasome substrates, and they display features characteristic of 20S substrates.","method":"Protein interactome dataset analysis, in vivo binding assays, cell-free (in vitro) degradation assays with recombinant C-terminal fragment, competitive inhibition experiments","journal":"Cells","confidence":"High","confidence_rationale":"Tier 1/2 — reconstituted in vitro with recombinant protein plus cell-based assays; multiple orthogonal approaches in single study","pmids":["36291102"],"is_preprint":false},{"year":2023,"finding":"The C-terminal region of PSMA3 is critical for 26S proteasome integrity. Truncation of the PSMA3 C-terminus phenocopies knockdown of the 19S regulatory particle subunit PSMD1, resulting in elevated levels of 'free' 20S core particles. Using CRISPR-tagged endogenous PSMB6-YFP and PSMD6-mScarlet, it was shown that free 20S CPs (without 19S caps) accumulate in the nucleus while PSMD6 (19S subunit) remains cytoplasmic under these conditions.","method":"CRISPR endogenous tagging (YFP, mScarlet), live-cell fluorescence microscopy, colocalization analysis, PSMA3 C-terminal truncation, PSMD1 siRNA knockdown","journal":"Biomolecules","confidence":"High","confidence_rationale":"Tier 1/2 — CRISPR endogenous tagging with live imaging plus genetic truncation; multiple orthogonal approaches establishing structural role","pmids":["37371572"],"is_preprint":false},{"year":2024,"finding":"The IDP p21 interacts with the PSMA3 C-terminal 'Trapper' region via a C-terminal RRLIF box, which acts as a ubiquitin-independent degron. CRISPR deletion or mutation of the p21 RRLIF box in HEK293 and HeLa cells increases p21 half-life, causes aberrant cell cycle patterns, and promotes senescence hallmark gene expression in response to DNA damage. The RRLIF box is positioned adjacent to the known ubiquitin-dependent degron, forming a dual degron module.","method":"Split luciferase reporter assay, p21 mutagenesis, CRISPR genome editing (HEK293 and HeLa), pulse-chase/half-life analysis, cell cycle analysis, senescence gene expression assays","journal":"bioRxiv","confidence":"High","confidence_rationale":"Tier 1 — reconstitution-level mutagenesis combined with CRISPR genome editing and multiple functional readouts in a single rigorous study","pmids":["bio_10.1101_2024.08.29.610237"],"is_preprint":true}],"current_model":"PSMA3 (alpha7/HC8) is the alpha-type subunit of the 20S proteasome whose C-terminal region acts as an 'IDP trapper' that recruits intrinsically disordered proteins (including p21 via its RRLIF degron box) for ubiquitin-independent degradation, is required for 26S proteasome integrity (its truncation liberates free 20S core particles), interacts with Aurora-B kinase and numerous splicing factors to link the proteasome to mRNA metabolism and mitotic regulation, and has a promoter driven by CAAT/TATA boxes whose activity—and the resulting proteasome levels—can be modulated by the antisense lncRNA PSMA3-AS1 through mRNA stabilization."},"narrative":{"teleology":[{"year":1995,"claim":"Isolation and characterization of the PSMA3 gene established that its promoter relies on CAAT and TATA boxes rather than GC boxes, distinguishing its transcriptional regulation from that of other proteasomal subunit genes and mapping the locus to 14q23.","evidence":"Gene isolation with CAT reporter promoter-deletion assays and chromosomal mapping","pmids":["7857283"],"confidence":"Medium","gaps":["No trans-acting factors for CAAT/TATA-dependent regulation identified","Functional consequence of promoter architecture for proteasome stoichiometry not tested"]},{"year":2003,"claim":"Demonstration that Aurora-B kinase physically binds PSMA3 and accumulates upon proteasome inhibition provided the first evidence that PSMA3 can recruit a specific mitotic regulator for proteasomal degradation.","evidence":"Yeast two-hybrid, GST pull-down, co-immunoprecipitation, and ALLN proteasome inhibitor treatment in HeLa cells","pmids":["14674694"],"confidence":"Medium","gaps":["Direct ubiquitin-independent versus ubiquitin-dependent degradation of Aurora-B via PSMA3 not distinguished","In vivo functional consequence of Aurora-B–PSMA3 interaction for mitosis not assessed"]},{"year":2011,"claim":"Proteomic identification of PSMA3 interactors enriched for splicing and mRNA-metabolism factors, combined with demonstration that the 20S proteasome regulates SMN2 splicing in vitro, expanded PSMA3's functional scope beyond proteolysis to mRNA processing.","evidence":"2D gel electrophoresis with MS/MS, in vitro co-immunoprecipitation with splicing factors, in vitro splicing assay","pmids":["22079093"],"confidence":"Medium","gaps":["Whether splicing regulation requires catalytic proteasome activity or a non-proteolytic PSMA3 scaffold function is unresolved","In vivo validation of proteasome-mediated splicing regulation not performed"]},{"year":2019,"claim":"Discovery that the antisense lncRNA PSMA3-AS1 forms an RNA duplex with pre-PSMA3 mRNA to stabilize it revealed a post-transcriptional feedback that controls 20S proteasome levels and showed that exosomal transfer of this duplex confers proteasome-inhibitor resistance in multiple myeloma.","evidence":"RNA duplex assay, siRNA knockdown, exosome characterization, co-culture, xenograft mouse model","pmids":["30610101"],"confidence":"Medium","gaps":["Precise RNA duplex structure and regulatory elements within pre-PSMA3 mRNA not mapped at nucleotide resolution","Contribution of PSMA3-AS1 to proteasome levels in non-myeloma contexts not explored"]},{"year":2022,"claim":"Reconstitution experiments established that the C-terminal 69-amino-acid segment of PSMA3 is an autonomous 'IDP trapper' sufficient to bind intrinsically disordered proteins and competitively inhibit their 20S-mediated degradation, defining the molecular basis of ubiquitin-independent substrate recruitment by the 20S proteasome.","evidence":"Recombinant C-terminal fragment, in vitro degradation and competitive inhibition assays, interactome analysis","pmids":["36291102"],"confidence":"High","gaps":["Structural basis of trapper–IDP recognition (e.g., cryo-EM or crystal structure) not resolved","Selectivity determinants distinguishing IDP substrates that use PSMA3 versus other alpha-ring entry routes remain unclear"]},{"year":2023,"claim":"CRISPR-based endogenous tagging revealed that the PSMA3 C-terminus is required for 26S proteasome integrity; its truncation liberates free 20S core particles that accumulate in the nucleus while 19S subunits remain cytoplasmic, establishing a structural gatekeeper role beyond substrate recruitment.","evidence":"CRISPR endogenous PSMB6-YFP and PSMD6-mScarlet tagging, live-cell microscopy, PSMA3 C-terminal truncation, PSMD1 siRNA","pmids":["37371572"],"confidence":"High","gaps":["Mechanism by which the C-terminus stabilizes the 19S–20S interface is not defined at the structural level","Physiological consequences of nuclear 20S accumulation not characterized"]},{"year":2024,"claim":"Identification of the p21 RRLIF box as a ubiquitin-independent degron that docks onto the PSMA3 trapper resolved how a key cell-cycle inhibitor is targeted for 20S degradation and showed that loss of this degron stabilizes p21, disrupts cell cycle, and promotes DNA-damage-induced senescence.","evidence":"Split luciferase binding assay, p21 mutagenesis, CRISPR deletion in HEK293/HeLa, pulse-chase half-life, cell cycle and senescence assays (preprint)","pmids":["bio_10.1101_2024.08.29.610237"],"confidence":"High","gaps":["Peer review pending; awaits independent replication","Whether other RRLIF-like degrons exist across the IDP trapper substrate repertoire is unknown","In vivo organismal consequence of RRLIF-box disruption not tested"]},{"year":null,"claim":"A structural model of the PSMA3 C-terminal trapper domain engaged with an IDP substrate (e.g., p21 RRLIF box) is missing, and the rules that govern substrate selectivity among the many IDPs captured by this region remain undefined.","evidence":"","pmids":[],"confidence":"High","gaps":["No high-resolution structure of trapper–substrate complex","Relative contribution of 20S (via PSMA3 trapper) versus 26S (ubiquitin-dependent) degradation of shared substrates in physiological settings not quantified","Non-proteolytic functions (splicing regulation) lack mechanistic detail"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[4,5]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[4,5,6]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[2,5]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[2,5]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[4,5,6]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[1,6]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[2]}],"complexes":["20S proteasome","26S proteasome"],"partners":["AURKB","CDKN1A","PSMD1","PSMA3-AS1"],"other_free_text":[]},"mechanistic_narrative":"PSMA3 (alpha7/HC8) is an alpha-type subunit of the 20S proteasome that serves dual roles in proteasome structure and substrate recruitment for ubiquitin-independent degradation. Its C-terminal 69-amino-acid region functions as an 'IDP trapper' that preferentially captures intrinsically disordered proteins—including p21, which it engages via a C-terminal RRLIF degron box—and delivers them for 20S-mediated proteolysis; CRISPR deletion of this degron stabilizes p21, disrupts cell cycle progression, and promotes senescence gene expression after DNA damage [PMID:36291102, PMID:bio_10.1101_2024.08.29.610237]. The PSMA3 C-terminus is also required for 26S proteasome integrity, as its truncation releases free 20S core particles that accumulate in the nucleus [PMID:37371572]. Beyond proteolysis, PSMA3 physically interacts with Aurora-B kinase and numerous splicing factors, linking the proteasome to mRNA processing and mitotic regulation [PMID:14674694, PMID:22079093], and its expression is modulated by the antisense lncRNA PSMA3-AS1, which stabilizes PSMA3 mRNA and can confer proteasome-inhibitor resistance in multiple myeloma [PMID:30610101]."},"prefetch_data":{"uniprot":{"accession":"P25788","full_name":"Proteasome subunit alpha type-3","aliases":["Macropain subunit C8","Multicatalytic endopeptidase complex subunit C8","Proteasome component C8","Proteasome subunit alpha-7","alpha-7"],"length_aa":255,"mass_kda":28.4,"function":"Component of the 20S core proteasome complex involved in the proteolytic degradation of most intracellular proteins. This complex plays numerous essential roles within the cell by associating with different regulatory particles. Associated with two 19S regulatory particles, forms the 26S proteasome and thus participates in the ATP-dependent degradation of ubiquitinated proteins. The 26S proteasome plays a key role in the maintenance of protein homeostasis by removing misfolded or damaged proteins that could impair cellular functions, and by removing proteins whose functions are no longer required. Associated with the PA200 or PA28, the 20S proteasome mediates ubiquitin-independent protein degradation. This type of proteolysis is required in several pathways including spermatogenesis (20S-PA200 complex) or generation of a subset of MHC class I-presented antigenic peptides (20S-PA28 complex). Binds to the C-terminus of CDKN1A and thereby mediates its degradation. Negatively regulates the membrane trafficking of the cell-surface thromboxane A2 receptor (TBXA2R) isoform 2","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/P25788/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/PSMA3","classification":"Common Essential","n_dependent_lines":1208,"n_total_lines":1208,"dependency_fraction":1.0},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000100567","cell_line_id":"CID000109","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"nucleoplasm","grade":3}],"interactors":[{"gene":"PSMD3","stoichiometry":10.0},{"gene":"PSMA5","stoichiometry":10.0},{"gene":"PSMB1","stoichiometry":10.0},{"gene":"PSMA2","stoichiometry":10.0},{"gene":"PSMD1","stoichiometry":10.0},{"gene":"PSMA4","stoichiometry":10.0},{"gene":"PSMC3","stoichiometry":10.0},{"gene":"UCHL5","stoichiometry":10.0},{"gene":"PSMD2","stoichiometry":10.0},{"gene":"PSMD6","stoichiometry":10.0}],"url":"https://opencell.sf.czbiohub.org/target/CID000109","total_profiled":1310},"omim":[{"mim_id":"613386","title":"PROTEASOME MATURATION PROTEIN; POMP","url":"https://www.omim.org/entry/613386"},{"mim_id":"606607","title":"PROTEASOME SUBUNIT, ALPHA-TYPE, 7; PSMA7","url":"https://www.omim.org/entry/606607"},{"mim_id":"606223","title":"PROTEASOME 26S SUBUNIT, NON-ATPASE, 2; PSMD2","url":"https://www.omim.org/entry/606223"},{"mim_id":"256040","title":"PROTEASOME-ASSOCIATED AUTOINFLAMMATORY SYNDROME 1; PRAAS1","url":"https://www.omim.org/entry/256040"},{"mim_id":"177046","title":"PROTEASOME SUBUNIT, BETA-TYPE, 8; PSMB8","url":"https://www.omim.org/entry/177046"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PSMA3"},"hgnc":{"alias_symbol":["HC8"],"prev_symbol":[]},"alphafold":{"accession":"P25788","domains":[{"cath_id":"3.60.20.10","chopping":"21-53_64-249","consensus_level":"high","plddt":96.8672,"start":21,"end":249}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P25788","model_url":"https://alphafold.ebi.ac.uk/files/AF-P25788-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P25788-F1-predicted_aligned_error_v6.png","plddt_mean":94.5},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PSMA3","jax_strain_url":"https://www.jax.org/strain/search?query=PSMA3"},"sequence":{"accession":"P25788","fasta_url":"https://rest.uniprot.org/uniprotkb/P25788.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P25788/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P25788"}},"corpus_meta":[{"pmid":"30610101","id":"PMC_30610101","title":"Exosome-Transmitted PSMA3 and 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Proteomic analysis using 2D gel electrophoresis and tandem mass spectrometry identified a large number of PSMA3-bound proteins in cytoplasm and nucleus involved in mRNA metabolism including splicing. In vitro biochemical studies confirmed interactions between PSMA3 and splicing factors. Moreover, the 20S proteasome was shown to regulate splicing of SMN2 in vitro.\",\n      \"method\": \"2D-GE, tandem mass spectrometry, in vitro biochemical binding assays, in vitro splicing assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (MS interactome + in vitro biochemical confirmation), single lab\",\n      \"pmids\": [\"22079093\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Aurora-B kinase binds directly to the PSMA3 (HC8) alpha-subunit of the 20S proteasome, and Aurora-B protein levels increase when proteasome activity is inhibited, suggesting Aurora-B undergoes proteasome-dependent degradation via its interaction with PSMA3.\",\n      \"method\": \"Yeast two-hybrid screen, GST pull-down assay, immunoprecipitation, proteasome inhibitor treatment in HeLa cells\",\n      \"journal\": \"Molecular and cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal binding confirmed by GST pulldown and Co-IP, functional consequence (protein stabilization upon inhibition) demonstrated\",\n      \"pmids\": [\"14674694\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The C-terminus of PSMA3 (a 69-amino-acid fragment) acts as an 'IDP trapper' that preferentially binds intrinsically disordered proteins (IDPs) to facilitate their degradation by the 20S proteasome. A recombinant C-terminal trapper fragment is sufficient for IDP interaction and blocks IDP degradation in vitro by competing with the native trapper. Many PSMA3 trapper-binding proteins are known 20S proteasome substrates.\",\n      \"method\": \"Protein interactome dataset analysis, in vivo and cell-free binding experiments, recombinant protein competition assay, in vitro degradation assay\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro reconstitution with recombinant fragments, competition assay, multiple orthogonal methods\",\n      \"pmids\": [\"36291102\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"The PSMA3 C-terminal region is critical for 26S proteasome integrity. Truncation of the PSMA3 C-terminus phenocopies PSMD1 knockdown (a 19S RP subunit), resulting in elevated 'free' 20S core particles with altered subcellular distribution, as visualized using CRISPR-tagged endogenous PSMB6-YFP and PSMD6-mScarlet fluorescent reporters.\",\n      \"method\": \"CRISPR tagging of endogenous proteasome subunits, live fluorescence imaging, PSMD1 knockdown, PSMA3 C-terminal truncation\",\n      \"journal\": \"Biomolecules\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — endogenous CRISPR tagging with functional genetic perturbation and direct imaging of subcellular consequences\",\n      \"pmids\": [\"37371572\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PSMA3 mRNA (and its antisense lncRNA PSMA3-AS1) can be packaged into exosomes by mesenchymal stem cells and transferred to multiple myeloma cells, promoting proteasome inhibitor resistance. PSMA3-AS1 forms an RNA duplex with pre-PSMA3 mRNA, increasing its stability and transcriptional output, thereby upregulating PSMA3 protein and conferring resistance.\",\n      \"method\": \"Exosome characterization (DLS, TEM, Western blot), co-culture transfer experiments, siRNA knockdown, xenograft model with intravenous siRNA delivery\",\n      \"journal\": \"Clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — exosomal transfer confirmed by co-culture, RNA duplex mechanism proposed with in vitro functional readout; single lab\",\n      \"pmids\": [\"30610101\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"The PSMA3 (HC8) gene was isolated and its promoter characterized: CAAT and TATA boxes (but not GC box) are essential for promoter activity, contrasting with other proteasome subunit genes. The HC8 gene was mapped to chromosome 14q23.\",\n      \"method\": \"Gene isolation, chloramphenicol acetyltransferase (CAT) promoter assay, chromosomal mapping\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — direct promoter functional assay, but single lab, foundational characterization study\",\n      \"pmids\": [\"7857283\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The p21 RRLIF box at its C-terminus mediates interaction with the PSMA3 C-terminal trapper region, acting as a ubiquitin-independent degron for 20S proteasomal degradation. CRISPR deletion or mutation of the RRLIF box in HEK293 and HeLa cells increased p21 half-life and caused aberrant cell cycle patterns and elevated senescence hallmark gene expression in response to DNA damage.\",\n      \"method\": \"Split luciferase reporter assay, p21 mutagenesis, CRISPR genome editing, half-life measurement, cell cycle analysis, senescence gene expression profiling\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — CRISPR editing with mutagenesis, multiple orthogonal functional readouts, mechanistic validation via split luciferase\",\n      \"pmids\": [\"bio_10.1101_2024.08.29.610237\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"PSMA3 (alpha7/HC8) is the alpha-7 subunit of the 20S proteasome whose C-terminal region acts as an 'IDP trapper' that captures intrinsically disordered proteins (including p21 via its RRLIF degron box) to facilitate their ubiquitin-independent degradation by the 20S proteasome, while also being critical for 26S proteasome integrity; additionally, PSMA3 interacts with Aurora-B kinase (targeting it for proteasomal degradation) and with splicing factors to regulate mRNA processing, and its mRNA can be transferred between cells via exosomes to modulate proteasome inhibitor resistance.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll systematically classify each paper before extracting discoveries.\n\n**Classification:**\n\nCorpus papers [1]-[32]:\n- [1] PSMA3 mRNA + PSMA3-AS1 lncRNA in exosomes → The paper describes PSMA3 protein (mRNA transferred) AND PSMA3-AS1 (lncRNA). The mechanism involves PSMA3-AS1 stabilizing pre-PSMA3 mRNA → KEEP (has mechanistic content about PSMA3 protein expression regulation)\n- [2] PSMA3-AS1 lncRNA only → EXCLUDE (alt-locus product, lncRNA)\n- [3] Bacillus subtilis HC8 → EXCLUDE (symbol collision, bacteria)\n- [4] PSMA3 (alpha7) interactome → KEEP\n- [5] PSMA3-AS1 lncRNA → EXCLUDE\n- [6] PSMA3-AS1 lncRNA → EXCLUDE\n- [7] PSMA3-AS1 lncRNA → EXCLUDE\n- [8] PSMA3-AS1 lncRNA → EXCLUDE\n- [9] PSMA3-AS1 lncRNA → EXCLUDE\n- [10] Aurora-B binds HC8 (PSMA3) → KEEP\n- [11] PSMA3-AS1 lncRNA → EXCLUDE\n- [12] PSMA3-AS1 lncRNA → EXCLUDE\n- [13] PSMA3 SNP genetics → EXCLUDE (no mechanism)\n- [14] PSMA3-AS1 lncRNA → EXCLUDE\n- [15] PSMA3-AS1 lncRNA → EXCLUDE\n- [16] PSMA3-AS1 lncRNA → EXCLUDE\n- [17] HC8 gene isolation → KEEP (PSMA3 gene, promoter characterization)\n- [18] HC8 from Haemonchus contortus (parasite) → EXCLUDE (symbol collision, nematode parasite protein unrelated to human PSMA3)\n- [19] PSMA3 SNP population genetics → EXCLUDE (no mechanism)\n- [20] PSMA3 protein as biomarker → EXCLUDE (no mechanism)\n- [21] PSMA3-AS1 lncRNA expression study → EXCLUDE\n- [22] PSMA3 C-terminus traps IDPs → KEEP\n- [23] PSMA3-AS1 lncRNA → EXCLUDE\n- [24] PSMA3-AS1 lncRNA → EXCLUDE\n- [25] Antibodies against PSMA3 → KEEP (validates PSMA3 protein)\n- [26] PSMA3-AS1 lncRNA → EXCLUDE\n- [27] PSMA3-AS1 lncRNA → EXCLUDE\n- [28] PSMA3 C-terminus and 26S integrity → KEEP\n- [29] PSMA3-AS1 review → EXCLUDE\n- [30] Psma3 mRNA expression in rats → EXCLUDE (expression only)\n- [31] PSMA3 Trapper / p21 degron → KEEP (preprint, mechanistic)\n- [32] PSMA3 in HCM network → EXCLUDE (computational/expression)\n\nGene2pubmed papers: These are large-scale proteomics/interactome studies. Several (BioPlex papers) include PSMA3 as an identified interactor but don't study its mechanism specifically. The APOBEC3G/CEM15 papers are clearly alias collisions. Structure/function reviews of the 20S proteasome (PMID:8811196) describe the alpha-subunit barrel but not PSMA3 specifically. I'll note relevant ones.\n- PMID:8811196 (20S/26S structure review) → describes alpha-subunits generally, KEEP for general proteasome context but PSMA3 not specifically studied → EXCLUDE (no PSMA3-specific mechanism)\n- BioPlex papers (PMIDs 26186194, 28514442, 33961781, 32296183) → PSMA3 appears as interactor in large-scale data, no specific mechanism → EXCLUDE\n- APOBEC3G papers → EXCLUDE (alias collision, CEM15=APOBEC3G)\n- Phosphoproteomics papers → PSMA3 may be detected as phosphorylated but no specific mechanism → borderline; these are large-scale datasets\n- PMID:17081983 (Olsen phosphoproteomics) → PSMA3 phosphorylation detected in global screen → EXCLUDE (no specific mechanistic study)\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1995,\n      \"finding\": \"The PSMA3 (HC8) gene encoding the alpha-type subunit of the human 20S proteasome was isolated and characterized. Its promoter requires CAAT and TATA boxes (but not GC boxes) for activity, distinguishing it from other proteasomal subunit promoters. The HC8 gene was mapped to chromosome 14q23.\",\n      \"method\": \"Gene isolation, chloramphenicol acetyltransferase promoter assay, chromosomal mapping\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct promoter functional assay with deletion analysis in a single lab\",\n      \"pmids\": [\"7857283\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Human Aurora-B kinase physically interacts with PSMA3 (alpha7/HC8), a subunit of the 20S proteasome. Aurora-B protein levels increase when the proteasome is inhibited with ALLN, suggesting Aurora-B undergoes proteasome-dependent degradation mediated by its binding to PSMA3.\",\n      \"method\": \"Yeast two-hybrid screen, GST pull-down assay, co-immunoprecipitation, proteasome inhibitor (ALLN) treatment in HeLa cells\",\n      \"journal\": \"Molecular and cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — reciprocal binding confirmed by pull-down and Co-IP plus pharmacological evidence; single lab\",\n      \"pmids\": [\"14674694\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Proteomic profiling of PSMA3-interacting proteins in both cytoplasm and nucleus revealed a large set of partners involved in mRNA metabolism and splicing. In vitro biochemical studies confirmed direct interactions between PSMA3 and splicing factors. Furthermore, the 20S proteasome was shown to regulate splicing of the SMN2 gene in vitro, establishing a functional link between the proteasome (via PSMA3) and mRNA processing.\",\n      \"method\": \"2D gel electrophoresis, tandem mass spectrometry (MS/MS), in vitro co-immunoprecipitation with splicing factors, in vitro splicing assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (MS interactome + in vitro binding + functional splicing assay) in a single lab\",\n      \"pmids\": [\"22079093\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PSMA3-AS1 (an antisense lncRNA) forms an RNA duplex with pre-PSMA3 mRNA and promotes PSMA3 expression by increasing its mRNA stability, thereby upregulating 20S proteasome levels and conferring proteasome inhibitor resistance in multiple myeloma cells. Exosomal transfer of PSMA3 and PSMA3-AS1 from mesenchymal stem cells to myeloma cells mediates this resistance.\",\n      \"method\": \"Exosome characterization (DLS, TEM, Western blot), co-culture experiments, siRNA knockdown, xenograft mouse model, RNA duplex interaction assay\",\n      \"journal\": \"Clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — multiple methods including in vivo validation; mechanism of PSMA3 mRNA stabilization by lncRNA duplex is central finding relevant to PSMA3 protein expression\",\n      \"pmids\": [\"30610101\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The C-terminal 69-amino-acid region of PSMA3 (alpha7 subunit of the 20S proteasome) functions as an 'IDP trapper' that preferentially binds intrinsically disordered proteins (IDPs). A recombinant trapper fragment is sufficient to interact with multiple IDPs and competitively blocks their degradation by the 20S proteasome in vitro. Over one-third of PSMA3 trapper-binding proteins are known 20S proteasome substrates, and they display features characteristic of 20S substrates.\",\n      \"method\": \"Protein interactome dataset analysis, in vivo binding assays, cell-free (in vitro) degradation assays with recombinant C-terminal fragment, competitive inhibition experiments\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — reconstituted in vitro with recombinant protein plus cell-based assays; multiple orthogonal approaches in single study\",\n      \"pmids\": [\"36291102\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"The C-terminal region of PSMA3 is critical for 26S proteasome integrity. Truncation of the PSMA3 C-terminus phenocopies knockdown of the 19S regulatory particle subunit PSMD1, resulting in elevated levels of 'free' 20S core particles. Using CRISPR-tagged endogenous PSMB6-YFP and PSMD6-mScarlet, it was shown that free 20S CPs (without 19S caps) accumulate in the nucleus while PSMD6 (19S subunit) remains cytoplasmic under these conditions.\",\n      \"method\": \"CRISPR endogenous tagging (YFP, mScarlet), live-cell fluorescence microscopy, colocalization analysis, PSMA3 C-terminal truncation, PSMD1 siRNA knockdown\",\n      \"journal\": \"Biomolecules\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — CRISPR endogenous tagging with live imaging plus genetic truncation; multiple orthogonal approaches establishing structural role\",\n      \"pmids\": [\"37371572\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The IDP p21 interacts with the PSMA3 C-terminal 'Trapper' region via a C-terminal RRLIF box, which acts as a ubiquitin-independent degron. CRISPR deletion or mutation of the p21 RRLIF box in HEK293 and HeLa cells increases p21 half-life, causes aberrant cell cycle patterns, and promotes senescence hallmark gene expression in response to DNA damage. The RRLIF box is positioned adjacent to the known ubiquitin-dependent degron, forming a dual degron module.\",\n      \"method\": \"Split luciferase reporter assay, p21 mutagenesis, CRISPR genome editing (HEK293 and HeLa), pulse-chase/half-life analysis, cell cycle analysis, senescence gene expression assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution-level mutagenesis combined with CRISPR genome editing and multiple functional readouts in a single rigorous study\",\n      \"pmids\": [\"bio_10.1101_2024.08.29.610237\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"PSMA3 (alpha7/HC8) is the alpha-type subunit of the 20S proteasome whose C-terminal region acts as an 'IDP trapper' that recruits intrinsically disordered proteins (including p21 via its RRLIF degron box) for ubiquitin-independent degradation, is required for 26S proteasome integrity (its truncation liberates free 20S core particles), interacts with Aurora-B kinase and numerous splicing factors to link the proteasome to mRNA metabolism and mitotic regulation, and has a promoter driven by CAAT/TATA boxes whose activity—and the resulting proteasome levels—can be modulated by the antisense lncRNA PSMA3-AS1 through mRNA stabilization.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"PSMA3 is the alpha-7 subunit of the 20S proteasome that functions as a substrate-recognition gateway for ubiquitin-independent protein degradation. Its C-terminal region (69 amino acids) acts as an intrinsically disordered protein (IDP) trapper that preferentially captures disordered substrates—including p21 via its RRLIF degron box—and delivers them for 20S proteasomal degradation, while also being critical for 26S proteasome assembly integrity, as its truncation leads to accumulation of free 20S particles with altered subcellular distribution [PMID:36291102, PMID:37371572]. PSMA3 additionally interacts with Aurora-B kinase to target it for proteasome-dependent degradation and associates with splicing factors to regulate mRNA processing, including SMN2 splicing [PMID:14674694, PMID:22079093]. PSMA3 mRNA stability is regulated by the antisense lncRNA PSMA3-AS1 via RNA duplex formation, and exosomal transfer of both transcripts from mesenchymal stem cells to myeloma cells promotes proteasome inhibitor resistance [PMID:30610101].\",\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"Establishing the basic gene architecture of PSMA3 revealed that its promoter relies on CAAT and TATA boxes rather than GC boxes, distinguishing it from other proteasome subunit genes and mapping it to chromosome 14q23.\",\n      \"evidence\": \"Gene isolation, CAT promoter assay, and chromosomal mapping\",\n      \"pmids\": [\"7857283\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No functional characterization of the encoded protein beyond gene structure\",\n        \"No information on how PSMA3 expression is regulated in different cell types\"\n      ]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Discovery that Aurora-B kinase directly binds PSMA3 and accumulates upon proteasome inhibition established PSMA3 as a proteasome subunit capable of mediating substrate-specific recognition for degradation.\",\n      \"evidence\": \"Yeast two-hybrid, GST pull-down, co-immunoprecipitation, and proteasome inhibitor treatment in HeLa cells\",\n      \"pmids\": [\"14674694\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether Aurora-B degradation is ubiquitin-dependent or -independent through PSMA3 was not resolved\",\n        \"No in vivo degradation kinetics measured\",\n        \"No identification of the PSMA3 domain mediating Aurora-B binding\"\n      ]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Proteomic identification of PSMA3-bound splicing factors and demonstration that the 20S proteasome regulates SMN2 splicing in vitro expanded PSMA3's functional repertoire beyond proteolysis to mRNA metabolism.\",\n      \"evidence\": \"2D-GE, tandem mass spectrometry interactomics, in vitro biochemical binding, and in vitro splicing assay\",\n      \"pmids\": [\"22079093\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether PSMA3-splicing factor interactions reflect a proteolytic or non-proteolytic function is unresolved\",\n        \"In vivo splicing regulation by PSMA3 not demonstrated\",\n        \"Single laboratory finding\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Demonstration that PSMA3 mRNA and its antisense lncRNA PSMA3-AS1 are transferred via exosomes from stromal cells to myeloma cells, stabilizing PSMA3 mRNA and conferring proteasome inhibitor resistance, linked PSMA3 expression regulation to the tumor microenvironment.\",\n      \"evidence\": \"Exosome characterization, co-culture transfer, siRNA knockdown, and xenograft model\",\n      \"pmids\": [\"30610101\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism of selective RNA packaging into exosomes not defined\",\n        \"Whether this resistance mechanism operates in non-myeloma cancers is unknown\",\n        \"Single laboratory with co-culture system\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identification of the PSMA3 C-terminal 69-amino-acid fragment as an 'IDP trapper' that preferentially captures intrinsically disordered proteins for ubiquitin-independent 20S degradation provided the first structural-mechanistic basis for how the 20S proteasome recognizes substrates without ubiquitin.\",\n      \"evidence\": \"Interactome analysis, recombinant protein binding and competition assays, in vitro degradation assays\",\n      \"pmids\": [\"36291102\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No atomic-resolution structure of the trapper–substrate complex\",\n        \"Whether all IDP substrates use the same trapper-binding mode is unknown\",\n        \"In vivo validation of trapper function limited\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Truncation of the PSMA3 C-terminus phenocopied 19S subunit loss, establishing that this region is essential not only for IDP trapping but also for maintaining 26S proteasome assembly.\",\n      \"evidence\": \"CRISPR tagging of endogenous PSMB6-YFP and PSMD6-mScarlet, live imaging, PSMD1 knockdown comparison\",\n      \"pmids\": [\"37371572\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis for how the C-terminus mediates 19S–20S association is unknown\",\n        \"Whether 26S disassembly from C-terminal truncation affects ubiquitin-dependent degradation globally was not quantified\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identification of the p21 RRLIF box as a specific ubiquitin-independent degron recognized by the PSMA3 C-terminal trapper provided a defined degron–receptor pair for 20S-mediated degradation and linked this mechanism to cell cycle control and senescence. (preprint)\",\n      \"evidence\": \"Split luciferase reporter, CRISPR mutagenesis of endogenous p21 in HEK293/HeLa, half-life measurement, cell cycle and senescence analysis\",\n      \"pmids\": [\"bio_10.1101_2024.08.29.610237\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Preprint; not yet peer-reviewed\",\n        \"Whether other RRLIF-like degrons exist in additional 20S substrates is unexplored\",\n        \"No structural model of the RRLIF–trapper interaction\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A high-resolution structure of the PSMA3 C-terminal trapper in complex with an IDP substrate or degron peptide, and in vivo validation of the trapper's role in global IDP turnover across cell types, remain to be established.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No structural model of the trapper–substrate interface\",\n        \"Relative contribution of PSMA3 trapper versus other 20S gating mechanisms to IDP degradation in vivo is undefined\",\n        \"Whether the splicing-regulatory role of PSMA3 is proteolysis-dependent remains unknown\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [2, 3, 6]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [2, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [1, 2, 3, 6]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"complexes\": [\n      \"20S proteasome\",\n      \"26S proteasome\"\n    ],\n    \"partners\": [\n      \"AURKB\",\n      \"CDKN1A\",\n      \"PSMA3-AS1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"PSMA3 (alpha7/HC8) is an alpha-type subunit of the 20S proteasome that serves dual roles in proteasome structure and substrate recruitment for ubiquitin-independent degradation. Its C-terminal 69-amino-acid region functions as an 'IDP trapper' that preferentially captures intrinsically disordered proteins—including p21, which it engages via a C-terminal RRLIF degron box—and delivers them for 20S-mediated proteolysis; CRISPR deletion of this degron stabilizes p21, disrupts cell cycle progression, and promotes senescence gene expression after DNA damage [PMID:36291102, PMID:bio_10.1101_2024.08.29.610237]. The PSMA3 C-terminus is also required for 26S proteasome integrity, as its truncation releases free 20S core particles that accumulate in the nucleus [PMID:37371572]. Beyond proteolysis, PSMA3 physically interacts with Aurora-B kinase and numerous splicing factors, linking the proteasome to mRNA processing and mitotic regulation [PMID:14674694, PMID:22079093], and its expression is modulated by the antisense lncRNA PSMA3-AS1, which stabilizes PSMA3 mRNA and can confer proteasome-inhibitor resistance in multiple myeloma [PMID:30610101].\",\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"Isolation and characterization of the PSMA3 gene established that its promoter relies on CAAT and TATA boxes rather than GC boxes, distinguishing its transcriptional regulation from that of other proteasomal subunit genes and mapping the locus to 14q23.\",\n      \"evidence\": \"Gene isolation with CAT reporter promoter-deletion assays and chromosomal mapping\",\n      \"pmids\": [\"7857283\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No trans-acting factors for CAAT/TATA-dependent regulation identified\",\n        \"Functional consequence of promoter architecture for proteasome stoichiometry not tested\"\n      ]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstration that Aurora-B kinase physically binds PSMA3 and accumulates upon proteasome inhibition provided the first evidence that PSMA3 can recruit a specific mitotic regulator for proteasomal degradation.\",\n      \"evidence\": \"Yeast two-hybrid, GST pull-down, co-immunoprecipitation, and ALLN proteasome inhibitor treatment in HeLa cells\",\n      \"pmids\": [\"14674694\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct ubiquitin-independent versus ubiquitin-dependent degradation of Aurora-B via PSMA3 not distinguished\",\n        \"In vivo functional consequence of Aurora-B–PSMA3 interaction for mitosis not assessed\"\n      ]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Proteomic identification of PSMA3 interactors enriched for splicing and mRNA-metabolism factors, combined with demonstration that the 20S proteasome regulates SMN2 splicing in vitro, expanded PSMA3's functional scope beyond proteolysis to mRNA processing.\",\n      \"evidence\": \"2D gel electrophoresis with MS/MS, in vitro co-immunoprecipitation with splicing factors, in vitro splicing assay\",\n      \"pmids\": [\"22079093\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether splicing regulation requires catalytic proteasome activity or a non-proteolytic PSMA3 scaffold function is unresolved\",\n        \"In vivo validation of proteasome-mediated splicing regulation not performed\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Discovery that the antisense lncRNA PSMA3-AS1 forms an RNA duplex with pre-PSMA3 mRNA to stabilize it revealed a post-transcriptional feedback that controls 20S proteasome levels and showed that exosomal transfer of this duplex confers proteasome-inhibitor resistance in multiple myeloma.\",\n      \"evidence\": \"RNA duplex assay, siRNA knockdown, exosome characterization, co-culture, xenograft mouse model\",\n      \"pmids\": [\"30610101\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Precise RNA duplex structure and regulatory elements within pre-PSMA3 mRNA not mapped at nucleotide resolution\",\n        \"Contribution of PSMA3-AS1 to proteasome levels in non-myeloma contexts not explored\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Reconstitution experiments established that the C-terminal 69-amino-acid segment of PSMA3 is an autonomous 'IDP trapper' sufficient to bind intrinsically disordered proteins and competitively inhibit their 20S-mediated degradation, defining the molecular basis of ubiquitin-independent substrate recruitment by the 20S proteasome.\",\n      \"evidence\": \"Recombinant C-terminal fragment, in vitro degradation and competitive inhibition assays, interactome analysis\",\n      \"pmids\": [\"36291102\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis of trapper–IDP recognition (e.g., cryo-EM or crystal structure) not resolved\",\n        \"Selectivity determinants distinguishing IDP substrates that use PSMA3 versus other alpha-ring entry routes remain unclear\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"CRISPR-based endogenous tagging revealed that the PSMA3 C-terminus is required for 26S proteasome integrity; its truncation liberates free 20S core particles that accumulate in the nucleus while 19S subunits remain cytoplasmic, establishing a structural gatekeeper role beyond substrate recruitment.\",\n      \"evidence\": \"CRISPR endogenous PSMB6-YFP and PSMD6-mScarlet tagging, live-cell microscopy, PSMA3 C-terminal truncation, PSMD1 siRNA\",\n      \"pmids\": [\"37371572\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Mechanism by which the C-terminus stabilizes the 19S–20S interface is not defined at the structural level\",\n        \"Physiological consequences of nuclear 20S accumulation not characterized\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identification of the p21 RRLIF box as a ubiquitin-independent degron that docks onto the PSMA3 trapper resolved how a key cell-cycle inhibitor is targeted for 20S degradation and showed that loss of this degron stabilizes p21, disrupts cell cycle, and promotes DNA-damage-induced senescence.\",\n      \"evidence\": \"Split luciferase binding assay, p21 mutagenesis, CRISPR deletion in HEK293/HeLa, pulse-chase half-life, cell cycle and senescence assays (preprint)\",\n      \"pmids\": [\"bio_10.1101_2024.08.29.610237\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Peer review pending; awaits independent replication\",\n        \"Whether other RRLIF-like degrons exist across the IDP trapper substrate repertoire is unknown\",\n        \"In vivo organismal consequence of RRLIF-box disruption not tested\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A structural model of the PSMA3 C-terminal trapper domain engaged with an IDP substrate (e.g., p21 RRLIF box) is missing, and the rules that govern substrate selectivity among the many IDPs captured by this region remain undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No high-resolution structure of trapper–substrate complex\",\n        \"Relative contribution of 20S (via PSMA3 trapper) versus 26S (ubiquitin-dependent) degradation of shared substrates in physiological settings not quantified\",\n        \"Non-proteolytic functions (splicing regulation) lack mechanistic detail\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [4, 5]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [4, 5, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [2, 5]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [2, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [4, 5, 6]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [1, 6]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"complexes\": [\n      \"20S proteasome\",\n      \"26S proteasome\"\n    ],\n    \"partners\": [\n      \"AURKB\",\n      \"CDKN1A\",\n      \"PSMD1\",\n      \"PSMA3-AS1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}