{"gene":"UTP18","run_date":"2026-06-11T09:02:06","timeline":{"discoveries":[{"year":2015,"finding":"Utp18 acts as an adaptor protein that recruits the exosome-associated helicase Mtr4 to cleaved rRNA fragments destined for degradation by the exosome. Utp18 contains an arch-interacting motif (AIM) through which it docks to the 'arch' (KOW) domain of Mtr4, targeting it to specific RNA substrates.","method":"Biochemical identification of adaptor proteins, interaction mapping, consensus motif identification","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal interaction mapping, consensus motif identified, replicated by structural study (PMID:28883156); multiple labs independently confirmed the AIM-Mtr4 interaction","pmids":["26317469"],"is_preprint":false},{"year":2017,"finding":"Atomic structure of the 90S preribosome at 3.2 Å resolution revealed the structural position of Utp18 within the assembly, showing how it is integrated into the highly intertwined network of assembly factors that guide pre-rRNA folding during 40S biogenesis.","method":"Cryo-EM structure determination at 3.2 Å resolution with atomic model building","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — high-resolution cryo-EM structure with atomic model building for Utp18 within the 90S preribosome","pmids":["28967883"],"is_preprint":false},{"year":2017,"finding":"Crystal structure of Mtr4 bound to the AIM-containing region of Nop53 (an analogue of Utp18) at 3.2 Å revealed that the KOW domain of Mtr4 recognizes the AIM sequence via hydrophobic and electrostatic interactions. NMR showed the KOW domain can simultaneously bind an AIM-containing protein and structured RNA at adjacent surfaces, explaining how Utp18/Nop53 adaptors dock the exosome onto RNPs.","method":"X-ray crystallography (3.2 Å), NMR spectroscopy","journal":"RNA (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus NMR with functional validation; AIM-Mtr4 interaction mechanism directly established for Utp18 class of adaptors","pmids":["28883156"],"is_preprint":false},{"year":2004,"finding":"Utp18 is a bona fide component of the SSU processome (small-subunit processome) required for 18S rRNA biogenesis, confirmed by co-immunoprecipitation with Mpp10, U3 snoRNA, and pre-rRNAs.","method":"Co-immunoprecipitation with SSU processome markers (Mpp10, U3 snoRNA, pre-rRNAs)","journal":"Eukaryotic cell","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — co-IP with multiple markers in a single study; replicated by Dosil & Bustelo (PMID:15231838)","pmids":["15590835"],"is_preprint":false},{"year":2004,"finding":"Utp18 is part of a stable subcomplex with Pwp2, Dip2, Utp6, Utp13, and Utp21 within the 90S pre-ribosome. This Pwp2-containing subcomplex directly interacts with the 5' end of the 35S pre-rRNA and is essential for initial assembly steps of the 90S pre-ribosome, functioning independently of the U3 snoRNP.","method":"Immunoprecipitation, gradient sedimentation analysis, pre-rRNA interaction assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP and sedimentation in single lab with two orthogonal methods; direct pre-rRNA interaction demonstrated","pmids":["15231838"],"is_preprint":false},{"year":2008,"finding":"Utp18 is a component of the UtpB subcomplex of the SSU processome, and the N-terminal domain of Utp6 directly interacts with Utp18, placing Utp18 in a defined architectural position within UtpB.","method":"Co-immunoprecipitation, interaction mapping with deletion mutants, biophysical methods","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct interaction mapped with deletion mutants and biophysical methods in single lab","pmids":["18725399"],"is_preprint":false},{"year":2014,"finding":"Human UTP18 localizes predominantly to the nucleolus (dense fibrillar component and granular component), but a subset localizes to the cytoplasm. Serum withdrawal increases cytoplasmic UTP18 localization. In the cytoplasm, UTP18 associates with the translation complex and Hsp90 to upregulate translation of IRES-containing transcripts (HIF1α, Myc, VEGF), promoting stress resistance. Hsp90 inhibition decreases cytoplasmic UTP18 and UTP18-induced translation increases.","method":"GFP live-cell imaging, FRAP, cellular fractionation, co-immunoprecipitation with translation complex and Hsp90, translation assays with IRES reporters","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (imaging, fractionation, co-IP, functional translation assay) in single lab; cytoplasmic localization tied to functional consequence","pmids":["25435373"],"is_preprint":false},{"year":2014,"finding":"In human HeLa cells, GFP-UTP18 (a UTP-B subcomplex component) localizes to the dense fibrillar component and granular component of nucleoli; when rRNA transcription is suppressed, the majority relocates to cap and body regions of nucleoli. Half of GFP-UTP18 shows low mobility by FRAP, consistent with tight association with macromolecular complexes acting as nucleolar scaffold.","method":"Live-cell GFP fluorescence imaging, FRAP, rRNA transcription inhibition","journal":"Biochemistry and cell biology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — live imaging and FRAP with functional perturbation (transcription inhibition) in single lab","pmids":["24754225"],"is_preprint":false},{"year":2023,"finding":"deSUMOylation of UTP18 induces its nucleocytoplasmic transport; once in the cytoplasm, UTP18 mediates instability of p21 mRNA, thereby driving cell-cycle progression and tumorigenesis in colorectal cancer.","method":"Quantitative proteomics, SUMOylation/deSUMOylation assays, mRNA stability assays, organoid overexpression experiments","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — SUMOylation modification identified with functional consequence (mRNA stability, cell cycle), single lab with multiple methods","pmids":["37086406"],"is_preprint":false},{"year":2025,"finding":"Within the yeast nucleolus, the exosome co-localizes with Mtr4 and Nop53 in the granular component, and Utp18 functions as an Mtr4-dependent adaptor facilitating exosome access to pre-ribosomal particles at this location.","method":"Fluorescence microscopy, subnucleolar localization comparison","journal":"Molecular biology of the cell","confidence":"Low","confidence_rationale":"Tier 3 / Weak — localization imaging in single lab; Utp18 role inferred from prior work and spatial co-localization without direct functional validation in this paper","pmids":["40266794"],"is_preprint":false}],"current_model":"UTP18 is a WD-repeat protein that functions in two distinct contexts: in the nucleolus, it is a core component of the UtpB subcomplex within the 90S preribosome/SSU processome, where it participates in pre-rRNA processing at sites A0, A1, and A2 to generate 18S rRNA; it also contains an arch-interacting motif (AIM) that directly docks onto the KOW domain of the RNA helicase Mtr4, recruiting the nuclear exosome to cleaved rRNA fragments for degradation. In a second, stress-responsive role, UTP18 translocates to the cytoplasm (regulated by deSUMOylation), where it associates with Hsp90 and the translation machinery to upregulate cap-independent (IRES-mediated) translation of transcripts such as HIF1α, Myc, and VEGF, and can also destabilize p21 mRNA to drive cell-cycle progression."},"narrative":{"mechanistic_narrative":"UTP18 is a WD-repeat assembly factor of ribosome biogenesis that operates as a core structural and adaptor component of the small-subunit (SSU) processome/90S preribosome required for 18S rRNA maturation [PMID:15590835, PMID:28967883]. It is a stable subunit of the Pwp2-containing UtpB subcomplex, where its N-terminal region is contacted directly by Utp6 to fix its architectural position, and this subcomplex engages the 5' end of the 35S pre-rRNA to drive initial 90S assembly steps independently of the U3 snoRNP [PMID:15231838, PMID:18725399]. Beyond its scaffolding role, UTP18 carries an arch-interacting motif (AIM) through which it docks onto the KOW domain of the RNA helicase Mtr4; structural and NMR analysis show the KOW domain simultaneously binds the AIM and structured RNA, allowing UTP18 to recruit the Mtr4-associated nuclear exosome onto cleaved pre-rRNA fragments for degradation [PMID:26317469, PMID:28883156]. In human cells, UTP18 resides predominantly in the nucleolar dense fibrillar and granular components but redistributes to cap and body regions upon transcription arrest [PMID:24754225]; a subset is exported to the cytoplasm, where, in association with Hsp90 and the translation machinery, it upregulates cap-independent (IRES-mediated) translation of HIF1α, Myc, and VEGF to promote stress resistance [PMID:25435373]. This nucleocytoplasmic shuttling is governed by deSUMOylation, and cytoplasmic UTP18 destabilizes p21 mRNA to drive cell-cycle progression and tumorigenesis in colorectal cancer [PMID:37086406].","teleology":[{"year":2004,"claim":"Established that UTP18 is a genuine ribosome biogenesis factor rather than an uncharacterized WD-repeat protein, placing it within the machinery that generates 18S rRNA.","evidence":"Co-immunoprecipitation with SSU processome markers Mpp10, U3 snoRNA, and pre-rRNAs; reciprocal co-IP and gradient sedimentation defining a Pwp2-containing subcomplex contacting the 5' end of 35S pre-rRNA","pmids":["15590835","15231838"],"confidence":"Medium","gaps":["Catalytic or structural contribution within the processome not resolved","Did not define direct binding partners at residue level"]},{"year":2008,"claim":"Resolved where UTP18 sits architecturally by mapping a direct Utp6-UTP18 contact, defining its position within the UtpB subcomplex.","evidence":"Co-immunoprecipitation and interaction mapping with deletion mutants plus biophysical methods","pmids":["18725399"],"confidence":"Medium","gaps":["Functional consequence of the Utp6 contact for assembly not directly tested","Full UtpB topology not established by this work alone"]},{"year":2014,"claim":"Revealed a second, non-ribosomal function: cytoplasmic UTP18 promotes cap-independent translation of stress transcripts, expanding its role beyond the nucleolus.","evidence":"GFP live-cell imaging, FRAP, fractionation, co-IP with translation machinery and Hsp90, and IRES reporter translation assays under serum withdrawal; separate imaging/FRAP showing nucleolar relocalization upon transcription arrest","pmids":["25435373","24754225"],"confidence":"Medium","gaps":["Mechanism by which UTP18 stimulates IRES translation not defined","Signal triggering cytoplasmic export not identified in this work"]},{"year":2015,"claim":"Defined the molecular basis for UTP18's role in rRNA surveillance, showing it acts as an adaptor that recruits Mtr4/exosome to substrate RNA via a defined motif.","evidence":"Biochemical adaptor identification, reciprocal interaction mapping, and AIM consensus motif identification docking to the Mtr4 KOW domain","pmids":["26317469"],"confidence":"High","gaps":["Atomic details of the AIM-KOW contact not yet resolved at this stage","In vivo kinetics of exosome recruitment not measured"]},{"year":2017,"claim":"Provided atomic-level mechanism for both the assembly and adaptor roles, fixing UTP18 within the 90S network and showing how the KOW domain binds AIM and RNA simultaneously.","evidence":"3.2 Å cryo-EM of the 90S preribosome with atomic model; 3.2 Å crystal structure of Mtr4 bound to an AIM peptide plus NMR mapping of simultaneous AIM/RNA binding","pmids":["28967883","28883156"],"confidence":"High","gaps":["AIM structure solved for Nop53 analogue rather than UTP18 itself","Dynamics of exosome handoff during processing not captured by static structures"]},{"year":2023,"claim":"Connected UTP18 localization control to disease, showing deSUMOylation drives cytoplasmic translocation where UTP18 destabilizes p21 mRNA to promote tumorigenesis.","evidence":"Quantitative proteomics, SUMOylation/deSUMOylation assays, mRNA stability assays, and organoid overexpression in colorectal cancer","pmids":["37086406"],"confidence":"Medium","gaps":["Direct mechanism of p21 mRNA destabilization (RNA binding vs. indirect) not established","SUMO sites and responsible enzymes not fully mapped"]},{"year":2025,"claim":"Refined the spatial context of UTP18-mediated surveillance, placing the exosome, Mtr4, and Nop53 with Utp18 in the nucleolar granular component.","evidence":"Fluorescence microscopy and subnucleolar localization comparison in yeast","pmids":["40266794"],"confidence":"Low","gaps":["Utp18 role inferred from co-localization without direct functional validation in this study","Causal contribution of granular-component positioning to exosome access untested"]},{"year":null,"claim":"How UTP18 is partitioned between its nucleolar biogenesis/surveillance roles and its cytoplasmic translation-regulatory role, and whether the same molecular surfaces are used, remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structural basis for cytoplasmic UTP18-Hsp90/translation machinery interaction","Unclear whether cytoplasmic functions require the AIM or WD-repeat surfaces used in the nucleolus"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,2]},{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[4]},{"term_id":"GO:0045182","term_label":"translation regulator activity","supporting_discovery_ids":[6]}],"localization":[{"term_id":"GO:0005730","term_label":"nucleolus","supporting_discovery_ids":[6,7]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[6,8]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[0,3,4]},{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[1,3]}],"complexes":["SSU processome / 90S preribosome","UtpB subcomplex"],"partners":["MTR4","UTP6","PWP2","DIP2","UTP13","UTP21","MPP10","HSP90"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9Y5J1","full_name":"U3 small nucleolar RNA-associated protein 18 homolog","aliases":["WD repeat-containing protein 50"],"length_aa":556,"mass_kda":62.0,"function":"Part of the small subunit (SSU) processome, first precursor of the small eukaryotic ribosomal subunit. During the assembly of the SSU processome in the nucleolus, many ribosome biogenesis factors, an RNA chaperone and ribosomal proteins associate with the nascent pre-rRNA and work in concert to generate RNA folding, modifications, rearrangements and cleavage as well as targeted degradation of pre-ribosomal RNA by the RNA exosome. Involved in nucleolar processing of pre-18S ribosomal RNA","subcellular_location":"Nucleus, nucleolus","url":"https://www.uniprot.org/uniprotkb/Q9Y5J1/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/UTP18","classification":"Common Essential","n_dependent_lines":1159,"n_total_lines":1208,"dependency_fraction":0.9594370860927153},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/UTP18","total_profiled":1310},"omim":[{"mim_id":"620948","title":"UTP6 SMALL SUBUNIT PROCESSOME COMPONENT; UTP6","url":"https://www.omim.org/entry/620948"},{"mim_id":"612816","title":"UTP18 SMALL SUBUNIT PROCESSOME COMPONENT; UTP18","url":"https://www.omim.org/entry/612816"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoli","reliability":"Supported"},{"location":"Nucleoli rim","reliability":"Supported"},{"location":"Nucleoplasm","reliability":"Additional"},{"location":"Nuclear membrane","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/UTP18"},"hgnc":{"alias_symbol":["CGI-48"],"prev_symbol":["WDR50"]},"alphafold":{"accession":"Q9Y5J1","domains":[{"cath_id":"2.130.10.10","chopping":"239-551","consensus_level":"high","plddt":91.3342,"start":239,"end":551}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y5J1","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y5J1-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y5J1-F1-predicted_aligned_error_v6.png","plddt_mean":78.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=UTP18","jax_strain_url":"https://www.jax.org/strain/search?query=UTP18"},"sequence":{"accession":"Q9Y5J1","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9Y5J1.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9Y5J1/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y5J1"}},"corpus_meta":[{"pmid":"26317469","id":"PMC_26317469","title":"The Exosome Is Recruited to RNA Substrates through Specific Adaptor Proteins.","date":"2015","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/26317469","citation_count":169,"is_preprint":false},{"pmid":"15590835","id":"PMC_15590835","title":"The small-subunit processome is a ribosome assembly intermediate.","date":"2004","source":"Eukaryotic cell","url":"https://pubmed.ncbi.nlm.nih.gov/15590835","citation_count":142,"is_preprint":false},{"pmid":"28967883","id":"PMC_28967883","title":"3.2-Å-resolution structure of the 90S preribosome before A1 pre-rRNA cleavage.","date":"2017","source":"Nature structural & molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/28967883","citation_count":90,"is_preprint":false},{"pmid":"15231838","id":"PMC_15231838","title":"Functional characterization of Pwp2, a WD family protein essential for the assembly of the 90 S pre-ribosomal particle.","date":"2004","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/15231838","citation_count":75,"is_preprint":false},{"pmid":"18725399","id":"PMC_18725399","title":"A direct interaction between the Utp6 half-a-tetratricopeptide repeat domain and a specific peptide in Utp21 is essential for efficient pre-rRNA processing.","date":"2008","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/18725399","citation_count":42,"is_preprint":false},{"pmid":"28883156","id":"PMC_28883156","title":"Structural insights into the interaction of the nuclear exosome helicase Mtr4 with the preribosomal protein Nop53.","date":"2017","source":"RNA (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/28883156","citation_count":37,"is_preprint":false},{"pmid":"24754225","id":"PMC_24754225","title":"Dynamics of WD-repeat containing proteins in SSU processome components.","date":"2014","source":"Biochemistry and cell biology = Biochimie et biologie cellulaire","url":"https://pubmed.ncbi.nlm.nih.gov/24754225","citation_count":17,"is_preprint":false},{"pmid":"37086406","id":"PMC_37086406","title":"UTP18-mediated p21 mRNA instability drives adenoma-carcinoma progression in colorectal cancer.","date":"2023","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/37086406","citation_count":10,"is_preprint":false},{"pmid":"25435373","id":"PMC_25435373","title":"A small subunit processome protein promotes cancer by altering translation.","date":"2014","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/25435373","citation_count":10,"is_preprint":false},{"pmid":"25269814","id":"PMC_25269814","title":"Genome-wide screening of Saccharomyces cerevisiae genes regulated by vanillin.","date":"2015","source":"Journal of microbiology and biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/25269814","citation_count":5,"is_preprint":false},{"pmid":"30099677","id":"PMC_30099677","title":"Genome-wide evidences of bisphenol a toxicity using Schizosaccharomyces pombe.","date":"2018","source":"Archives of pharmacal research","url":"https://pubmed.ncbi.nlm.nih.gov/30099677","citation_count":4,"is_preprint":false},{"pmid":"40266794","id":"PMC_40266794","title":"New insights into nuclear import and nucleolar localization of yeast RNA exosome subunits.","date":"2025","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/40266794","citation_count":1,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7400,"output_tokens":2519,"usd":0.029992,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9640,"output_tokens":2917,"usd":0.060562,"stage2_stop_reason":"end_turn"},"total_usd":0.090554,"stage1_batch_id":"msgbatch_01UT1AahFPCAyn2uVweS7A9z","stage2_batch_id":"msgbatch_01HuKWtKNT4Pqj1bc8eEP5RV","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2015,\n      \"finding\": \"Utp18 acts as an adaptor protein that recruits the exosome-associated helicase Mtr4 to cleaved rRNA fragments destined for degradation by the exosome. Utp18 contains an arch-interacting motif (AIM) through which it docks to the 'arch' (KOW) domain of Mtr4, targeting it to specific RNA substrates.\",\n      \"method\": \"Biochemical identification of adaptor proteins, interaction mapping, consensus motif identification\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal interaction mapping, consensus motif identified, replicated by structural study (PMID:28883156); multiple labs independently confirmed the AIM-Mtr4 interaction\",\n      \"pmids\": [\"26317469\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Atomic structure of the 90S preribosome at 3.2 Å resolution revealed the structural position of Utp18 within the assembly, showing how it is integrated into the highly intertwined network of assembly factors that guide pre-rRNA folding during 40S biogenesis.\",\n      \"method\": \"Cryo-EM structure determination at 3.2 Å resolution with atomic model building\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — high-resolution cryo-EM structure with atomic model building for Utp18 within the 90S preribosome\",\n      \"pmids\": [\"28967883\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Crystal structure of Mtr4 bound to the AIM-containing region of Nop53 (an analogue of Utp18) at 3.2 Å revealed that the KOW domain of Mtr4 recognizes the AIM sequence via hydrophobic and electrostatic interactions. NMR showed the KOW domain can simultaneously bind an AIM-containing protein and structured RNA at adjacent surfaces, explaining how Utp18/Nop53 adaptors dock the exosome onto RNPs.\",\n      \"method\": \"X-ray crystallography (3.2 Å), NMR spectroscopy\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus NMR with functional validation; AIM-Mtr4 interaction mechanism directly established for Utp18 class of adaptors\",\n      \"pmids\": [\"28883156\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Utp18 is a bona fide component of the SSU processome (small-subunit processome) required for 18S rRNA biogenesis, confirmed by co-immunoprecipitation with Mpp10, U3 snoRNA, and pre-rRNAs.\",\n      \"method\": \"Co-immunoprecipitation with SSU processome markers (Mpp10, U3 snoRNA, pre-rRNAs)\",\n      \"journal\": \"Eukaryotic cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — co-IP with multiple markers in a single study; replicated by Dosil & Bustelo (PMID:15231838)\",\n      \"pmids\": [\"15590835\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Utp18 is part of a stable subcomplex with Pwp2, Dip2, Utp6, Utp13, and Utp21 within the 90S pre-ribosome. This Pwp2-containing subcomplex directly interacts with the 5' end of the 35S pre-rRNA and is essential for initial assembly steps of the 90S pre-ribosome, functioning independently of the U3 snoRNP.\",\n      \"method\": \"Immunoprecipitation, gradient sedimentation analysis, pre-rRNA interaction assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP and sedimentation in single lab with two orthogonal methods; direct pre-rRNA interaction demonstrated\",\n      \"pmids\": [\"15231838\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Utp18 is a component of the UtpB subcomplex of the SSU processome, and the N-terminal domain of Utp6 directly interacts with Utp18, placing Utp18 in a defined architectural position within UtpB.\",\n      \"method\": \"Co-immunoprecipitation, interaction mapping with deletion mutants, biophysical methods\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct interaction mapped with deletion mutants and biophysical methods in single lab\",\n      \"pmids\": [\"18725399\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Human UTP18 localizes predominantly to the nucleolus (dense fibrillar component and granular component), but a subset localizes to the cytoplasm. Serum withdrawal increases cytoplasmic UTP18 localization. In the cytoplasm, UTP18 associates with the translation complex and Hsp90 to upregulate translation of IRES-containing transcripts (HIF1α, Myc, VEGF), promoting stress resistance. Hsp90 inhibition decreases cytoplasmic UTP18 and UTP18-induced translation increases.\",\n      \"method\": \"GFP live-cell imaging, FRAP, cellular fractionation, co-immunoprecipitation with translation complex and Hsp90, translation assays with IRES reporters\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (imaging, fractionation, co-IP, functional translation assay) in single lab; cytoplasmic localization tied to functional consequence\",\n      \"pmids\": [\"25435373\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In human HeLa cells, GFP-UTP18 (a UTP-B subcomplex component) localizes to the dense fibrillar component and granular component of nucleoli; when rRNA transcription is suppressed, the majority relocates to cap and body regions of nucleoli. Half of GFP-UTP18 shows low mobility by FRAP, consistent with tight association with macromolecular complexes acting as nucleolar scaffold.\",\n      \"method\": \"Live-cell GFP fluorescence imaging, FRAP, rRNA transcription inhibition\",\n      \"journal\": \"Biochemistry and cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — live imaging and FRAP with functional perturbation (transcription inhibition) in single lab\",\n      \"pmids\": [\"24754225\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"deSUMOylation of UTP18 induces its nucleocytoplasmic transport; once in the cytoplasm, UTP18 mediates instability of p21 mRNA, thereby driving cell-cycle progression and tumorigenesis in colorectal cancer.\",\n      \"method\": \"Quantitative proteomics, SUMOylation/deSUMOylation assays, mRNA stability assays, organoid overexpression experiments\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — SUMOylation modification identified with functional consequence (mRNA stability, cell cycle), single lab with multiple methods\",\n      \"pmids\": [\"37086406\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Within the yeast nucleolus, the exosome co-localizes with Mtr4 and Nop53 in the granular component, and Utp18 functions as an Mtr4-dependent adaptor facilitating exosome access to pre-ribosomal particles at this location.\",\n      \"method\": \"Fluorescence microscopy, subnucleolar localization comparison\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — localization imaging in single lab; Utp18 role inferred from prior work and spatial co-localization without direct functional validation in this paper\",\n      \"pmids\": [\"40266794\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"UTP18 is a WD-repeat protein that functions in two distinct contexts: in the nucleolus, it is a core component of the UtpB subcomplex within the 90S preribosome/SSU processome, where it participates in pre-rRNA processing at sites A0, A1, and A2 to generate 18S rRNA; it also contains an arch-interacting motif (AIM) that directly docks onto the KOW domain of the RNA helicase Mtr4, recruiting the nuclear exosome to cleaved rRNA fragments for degradation. In a second, stress-responsive role, UTP18 translocates to the cytoplasm (regulated by deSUMOylation), where it associates with Hsp90 and the translation machinery to upregulate cap-independent (IRES-mediated) translation of transcripts such as HIF1α, Myc, and VEGF, and can also destabilize p21 mRNA to drive cell-cycle progression.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"UTP18 is a WD-repeat assembly factor of ribosome biogenesis that operates as a core structural and adaptor component of the small-subunit (SSU) processome/90S preribosome required for 18S rRNA maturation [#3, #1]. It is a stable subunit of the Pwp2-containing UtpB subcomplex, where its N-terminal region is contacted directly by Utp6 to fix its architectural position, and this subcomplex engages the 5' end of the 35S pre-rRNA to drive initial 90S assembly steps independently of the U3 snoRNP [#4, #5]. Beyond its scaffolding role, UTP18 carries an arch-interacting motif (AIM) through which it docks onto the KOW domain of the RNA helicase Mtr4; structural and NMR analysis show the KOW domain simultaneously binds the AIM and structured RNA, allowing UTP18 to recruit the Mtr4-associated nuclear exosome onto cleaved pre-rRNA fragments for degradation [#0, #2]. In human cells, UTP18 resides predominantly in the nucleolar dense fibrillar and granular components but redistributes to cap and body regions upon transcription arrest [#7]; a subset is exported to the cytoplasm, where, in association with Hsp90 and the translation machinery, it upregulates cap-independent (IRES-mediated) translation of HIF1\\u03b1, Myc, and VEGF to promote stress resistance [#6]. This nucleocytoplasmic shuttling is governed by deSUMOylation, and cytoplasmic UTP18 destabilizes p21 mRNA to drive cell-cycle progression and tumorigenesis in colorectal cancer [#8].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Established that UTP18 is a genuine ribosome biogenesis factor rather than an uncharacterized WD-repeat protein, placing it within the machinery that generates 18S rRNA.\",\n      \"evidence\": \"Co-immunoprecipitation with SSU processome markers Mpp10, U3 snoRNA, and pre-rRNAs; reciprocal co-IP and gradient sedimentation defining a Pwp2-containing subcomplex contacting the 5' end of 35S pre-rRNA\",\n      \"pmids\": [\"15590835\", \"15231838\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Catalytic or structural contribution within the processome not resolved\", \"Did not define direct binding partners at residue level\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Resolved where UTP18 sits architecturally by mapping a direct Utp6-UTP18 contact, defining its position within the UtpB subcomplex.\",\n      \"evidence\": \"Co-immunoprecipitation and interaction mapping with deletion mutants plus biophysical methods\",\n      \"pmids\": [\"18725399\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of the Utp6 contact for assembly not directly tested\", \"Full UtpB topology not established by this work alone\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Revealed a second, non-ribosomal function: cytoplasmic UTP18 promotes cap-independent translation of stress transcripts, expanding its role beyond the nucleolus.\",\n      \"evidence\": \"GFP live-cell imaging, FRAP, fractionation, co-IP with translation machinery and Hsp90, and IRES reporter translation assays under serum withdrawal; separate imaging/FRAP showing nucleolar relocalization upon transcription arrest\",\n      \"pmids\": [\"25435373\", \"24754225\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which UTP18 stimulates IRES translation not defined\", \"Signal triggering cytoplasmic export not identified in this work\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defined the molecular basis for UTP18's role in rRNA surveillance, showing it acts as an adaptor that recruits Mtr4/exosome to substrate RNA via a defined motif.\",\n      \"evidence\": \"Biochemical adaptor identification, reciprocal interaction mapping, and AIM consensus motif identification docking to the Mtr4 KOW domain\",\n      \"pmids\": [\"26317469\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic details of the AIM-KOW contact not yet resolved at this stage\", \"In vivo kinetics of exosome recruitment not measured\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Provided atomic-level mechanism for both the assembly and adaptor roles, fixing UTP18 within the 90S network and showing how the KOW domain binds AIM and RNA simultaneously.\",\n      \"evidence\": \"3.2 \\u00c5 cryo-EM of the 90S preribosome with atomic model; 3.2 \\u00c5 crystal structure of Mtr4 bound to an AIM peptide plus NMR mapping of simultaneous AIM/RNA binding\",\n      \"pmids\": [\"28967883\", \"28883156\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"AIM structure solved for Nop53 analogue rather than UTP18 itself\", \"Dynamics of exosome handoff during processing not captured by static structures\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Connected UTP18 localization control to disease, showing deSUMOylation drives cytoplasmic translocation where UTP18 destabilizes p21 mRNA to promote tumorigenesis.\",\n      \"evidence\": \"Quantitative proteomics, SUMOylation/deSUMOylation assays, mRNA stability assays, and organoid overexpression in colorectal cancer\",\n      \"pmids\": [\"37086406\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct mechanism of p21 mRNA destabilization (RNA binding vs. indirect) not established\", \"SUMO sites and responsible enzymes not fully mapped\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Refined the spatial context of UTP18-mediated surveillance, placing the exosome, Mtr4, and Nop53 with Utp18 in the nucleolar granular component.\",\n      \"evidence\": \"Fluorescence microscopy and subnucleolar localization comparison in yeast\",\n      \"pmids\": [\"40266794\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Utp18 role inferred from co-localization without direct functional validation in this study\", \"Causal contribution of granular-component positioning to exosome access untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How UTP18 is partitioned between its nucleolar biogenesis/surveillance roles and its cytoplasmic translation-regulatory role, and whether the same molecular surfaces are used, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structural basis for cytoplasmic UTP18-Hsp90/translation machinery interaction\", \"Unclear whether cytoplasmic functions require the AIM or WD-repeat surfaces used in the nucleolus\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"GO:0045182\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [6, 7]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [6, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [0, 3, 4]},\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [1, 3]}\n    ],\n    \"complexes\": [\n      \"SSU processome / 90S preribosome\",\n      \"UtpB subcomplex\"\n    ],\n    \"partners\": [\n      \"MTR4\",\n      \"UTP6\",\n      \"PWP2\",\n      \"DIP2\",\n      \"UTP13\",\n      \"UTP21\",\n      \"MPP10\",\n      \"HSP90\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}