{"gene":"NOP56","run_date":"2026-04-29T11:37:57","timeline":{"discoveries":[{"year":2006,"finding":"The coiled-coil domain of archaeal Nop56/58 is dispensable for sRNP assembly but critical for box C/D sRNP-guided nucleotide methylation. Nop56/58 self-dimerization and Nop56/58-fibrillarin dimerization are mutually exclusive protein-protein interactions. Deletion of the coiled-coil domain disrupts guided methylation from both box C/D and C'/D' RNP complexes and alters RNP structure, despite allowing functional complex assembly.","method":"Protein pull-down, site-directed mutagenesis, deletion constructs, in vitro methylation assay, nuclease probing of sRNP structure","journal":"RNA (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1 — in vitro methylation assay with mutagenesis and structural probing, multiple orthogonal methods","pmids":["16601205"],"is_preprint":false},{"year":2007,"finding":"Crystal structure of the archaeal Nop56/58-fibrillarin complex from Pyrococcus furiosus bound with S-adenosyl-L-methionine reveals a bipartite dimeric arrangement that is a general feature across species. The conformation of Nop56/58 in this structure differs substantially from the earlier Archaeoglobus fulgidus structure, indicating intrinsic conformational flexibility. Computational normal mode analysis supports hinge motion within Nop56/58, suggesting that such flexibility allows simultaneous positioning of two catalytic sites at two target sites of a bipartite box C/D guide RNA.","method":"X-ray crystallography (2.7 Å), computational normal mode analysis","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with functional interpretation and computational validation","pmids":["17617422"],"is_preprint":false},{"year":2009,"finding":"Fibrillarin and Nop56 directly interact in vivo before being co-assembled into box C/D snoRNPs. This interaction does not require the glycine- and arginine-rich domain or the RNA-binding domain of fibrillarin, but depends on the alpha-helix domain of fibrillarin. No RNA is required to maintain the fibrillarin-Nop56 interaction. Altering the localization and mobility of core box C/D proteins (including Nop56) impairs their association with box C/D snoRNPs.","method":"In vivo relocalization/affinity-tag approach (B23 tag), co-immunoprecipitation, fluorescence microscopy","journal":"Experimental cell research","confidence":"High","confidence_rationale":"Tier 2 — reciprocal in vivo interaction mapping with domain dissection and multiple orthogonal methods","pmids":["19331828"],"is_preprint":false},{"year":2012,"finding":"The N-terminal domain (NTD) of archaeal Nop56/58 mediates an exceptionally stable interaction with fibrillarin (confirmed by chemical and thermal denaturation). Only deletion of the NTD itself prevented dimerization with fibrillarin. Mutations in the NTD that did not affect fibrillarin binding or sRNP assembly nevertheless disrupted sRNP-guided nucleotide modification, revealing a direct role for Nop56/58 in methyltransferase activity beyond scaffold function. Cross-linking showed Nop56/58 contacts the target RNA substrate. The crystal structure of the Mj Nop56/58 NTD was solved to 1.7 Å, revealing a conserved fold among archaeal homologs despite low primary sequence conservation.","method":"Site-directed mutagenesis, chemical/thermal denaturation, in vitro methylation assay, RNA cross-linking, X-ray crystallography (1.7 Å)","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — crystal structure combined with mutagenesis, methylation assay, and RNA cross-linking in one study","pmids":["22496443"],"is_preprint":false},{"year":2013,"finding":"Nol5a/Nop56 was identified as a gene hyperactivated by Burkitt's lymphoma-associated Myc mutants. Nol5a is required for Myc-induced cell transformation: knockdown reduced transformation, while overexpression enhanced MycWT-induced transformation and increased tumor size. This establishes Nop56 as a rate-limiting nucleolar target gene downstream of Myc that links Myc-induced ribosomal RNA methylation to cell transformation.","method":"Gene expression profiling, siRNA knockdown, overexpression, cell transformation assay, in vivo tumor growth assay","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 — loss- and gain-of-function with cellular and in vivo phenotypic readouts, single lab","pmids":["24013231"],"is_preprint":false},{"year":2018,"finding":"The intron-hosted box C/D snoRNA snoRD86 acts in cis as a sensor and master switch controlling levels of the limiting snoRNP core protein NOP56. Excess snoRNP core proteins cause snoRD86 to adopt different RNP conformations that dictate usage of nearby alternative splice donors in the NOP56 pre-mRNA, triggering generation of a cytoplasmic snoRD86-containing NOP56-derived lncRNA via the nonsense-mediated decay (NMD) pathway. This constitutes a feedback mechanism based on RNA structure that coordinates box C/D snoRNP core protein levels and global snoRNA levels.","method":"RNA splicing analysis, NMD pathway assays, RNP structure analysis, snoRNA expression measurements, alternative splicing mapping","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal molecular methods establishing feedback mechanism, published in high-impact journal","pmids":["30220559"],"is_preprint":false},{"year":2021,"finding":"High-resolution crystal structure of eukaryotic (yeast) Nop1 (fibrillarin) bound to the amino-terminal domain of Nop56 reveals the protein-protein interface. The eukaryotic Nop56 NTD recruits the methyltransferase to the box C/D RNP through a protein-protein interface that differs substantially from archaeal orthologs, demonstrating evolutionary divergence in the mechanism of methyltransferase recruitment to the C/D RNP complex.","method":"X-ray crystallography (high-resolution structure), structural comparison with archaeal orthologs","journal":"RNA (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure with functional domain characterization","pmids":["33483369"],"is_preprint":false},{"year":2022,"finding":"Zebrafish nop56 loss-of-function mutants exhibit severe neurodegeneration characterized by absence of cerebellum, reduced numbers of spinal cord neurons, high CNS apoptosis, and impaired movement leading to death before 7 days post-fertilization. Gene expression of genes related to the C/D box complex, balance, and CNS development was impaired in mutants, establishing NOP56 as essential for CNS development and neuronal survival in a vertebrate model.","method":"Zebrafish loss-of-function genetic model, fluorescence microscopy, apoptosis assays, gene expression analysis, movement assays","journal":"Biomedicines","confidence":"Medium","confidence_rationale":"Tier 2 — clean loss-of-function vertebrate model with defined cellular and developmental phenotypes","pmids":["36009362"],"is_preprint":false},{"year":2022,"finding":"NOP56 depletion causes synthetic lethality with mTOR inhibition in KRAS-mutant lung cancer cells. Mechanistically, NOP56 regulates ROS homeostasis; cells with reduced NOP56 have elevated ROS and rely on mTOR signaling to balance oxidative stress. IRE1α-mediated unfolded protein response (UPR) activates mTOR through p38 MAPK under NOP56 depletion. Co-targeting NOP56 and mTOR profoundly enhances KRAS-mutant tumor cell death in vitro and in vivo.","method":"siRNA/shRNA knockdown, CRISPR/Cas9 knockout, flow cytometry (ROS measurement), Western blot, cell viability and apoptosis assays, xenograft tumor model","journal":"Journal of experimental & clinical cancer research : CR","confidence":"Medium","confidence_rationale":"Tier 2 — multiple genetic and pharmacological approaches with in vitro and in vivo validation, single lab","pmids":["35039048"],"is_preprint":false},{"year":2021,"finding":"NOP56 serves as a negative regulator of the MyD88-mediated NF-κB signaling pathway in teleost fish. NOP56 overexpression inhibited MyD88 protein expression, while siRNA knockdown had the opposite effect. The NOSIC domain of NOP56 is responsible for suppressing MyD88 expression at the protein level.","method":"Overexpression, siRNA knockdown, Western blot, domain deletion analysis","journal":"Fish & shellfish immunology","confidence":"Low","confidence_rationale":"Tier 3 — single lab, non-mammalian model (teleost fish), single method class for domain mapping","pmids":["34774735"],"is_preprint":false},{"year":2025,"finding":"NOP56 GGCCTG repeat-associated non-AUG (RAN) translation in cell-free systems occurs in all reading frames of the sense strand of NOP56 intron 1. Translation is initiated in a 5' cap-dependent manner from near-cognate start codons upstream of the GGCCUG repeat in each frame. Longer GGCCUG repeats enhance NOP56-RAN translation. A frameshift occurs within the GGCCUG repeat during translation.","method":"Cell-free translation systems, in vitro translation assays with repeat constructs of varying lengths, frameshifting analysis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1 — in vitro reconstitution with cell-free translation systems, mechanistic dissection of RAN translation","pmids":["40015643"],"is_preprint":false},{"year":2026,"finding":"NOP56 interacts with fibrillarin (FBL) in hepatocellular carcinoma cells and activates the PI3K/AKT/CREB pathway. NOP56 knockdown lowered FBL protein levels and suppressed PI3K/AKT/CREB pathway activity, inducing apoptosis and G0/G1 arrest. FBL overexpression partially rescued apoptotic effects of NOP56 silencing, establishing a NOP56-FBL-PI3K/AKT/CREB signaling axis in HCC.","method":"Co-immunoprecipitation, Western blot, siRNA knockdown, overexpression, xenograft tumor model, flow cytometry","journal":"Frontiers in oncology","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP plus rescue experiment with pathway analysis, single lab","pmids":["41568368"],"is_preprint":false},{"year":2026,"finding":"NOP56 activates MYC signaling by regulating IRES-dependent translation, which in turn transcriptionally upregulates NOP56 expression creating a positive feedback loop. NOP56 overexpression promotes ribosome biogenesis, cellular proliferation, and metastasis in non-small cell lung cancer. Hypomethylation of the NOP56 promoter contributes to its upregulation in NSCLC.","method":"RNA sequencing, qPCR, Western blot, luciferase reporter assay, chromatin immunoprecipitation (ChIP), bisulfite DNA sequencing, functional assays, in vivo tumor model","journal":"Cancers","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods (ChIP, bisulfite sequencing, luciferase, RNA-seq) establishing feedback mechanism, single lab","pmids":["41827688"],"is_preprint":false},{"year":2025,"finding":"UPR (unfolded protein response) activation significantly downregulates NOP56 expression along with other C/D box snoRNP core proteins (NHP2L1 and FBL). Reduced C/D box snoRNP function during UPR alters rRNA methylation and translational fidelity, including changes in nonsense suppression, frameshifting, ribosome pausing, and IRES-dependent translation initiation.","method":"qPCR/Western blot for expression, rRNA methylation assay, translational fidelity reporter assays (nonsense suppression, frameshift, IRES reporters), UPR induction","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 — preprint, single lab, NOP56 downregulation shown but mechanistic role attributed to collective snoRNP reduction","pmids":[],"is_preprint":true}],"current_model":"NOP56 is a conserved core component of box C/D snoRNP complexes that directly interacts with fibrillarin (through its N-terminal domain) and with the guide snoRNA to scaffold and facilitate 2'-O-methylation of rRNA nucleotides; its coiled-coil domain is required for proper RNP architecture and methyltransferase activity, its levels are autoregulated by a cis-acting snoRD86-based RNA structure feedback mechanism in the NOP56 pre-mRNA, and in cancer contexts NOP56 promotes ribosome biogenesis and cell transformation downstream of MYC while also regulating ROS homeostasis and mTOR-dependent survival signaling."},"narrative":{"teleology":[{"year":2006,"claim":"Determining whether the coiled-coil domain of Nop56/58 functions in snoRNP assembly or catalysis resolved its role: the domain is dispensable for RNP formation but essential for guided 2'-O-methylation and proper RNP architecture, and Nop56/58 self-dimerization and fibrillarin binding are mutually exclusive.","evidence":"In vitro methylation assays with deletion/mutation constructs and nuclease probing of archaeal sRNPs","pmids":["16601205"],"confidence":"High","gaps":["Whether the coiled-coil requirement is conserved in eukaryotic NOP56","Mechanism by which coiled-coil domain organizes dual catalytic sites"]},{"year":2007,"claim":"Solving the crystal structure of the archaeal Nop56/58–fibrillarin–SAM complex revealed a bipartite dimeric arrangement with intrinsic conformational flexibility, explaining how two catalytic sites can be positioned on a single bipartite C/D guide RNA.","evidence":"X-ray crystallography (2.7 Å) of Pyrococcus furiosus complex plus computational normal mode analysis","pmids":["17617422"],"confidence":"High","gaps":["No eukaryotic structure available at the time","Structural basis of substrate RNA engagement unresolved"]},{"year":2009,"claim":"In vivo interaction mapping established that fibrillarin and Nop56 form a pre-assembled heterodimer before incorporation into box C/D snoRNPs, with the fibrillarin α-helix domain but not its GAR or RNA-binding domains mediating the interaction.","evidence":"In vivo relocalization/affinity-tag approach with co-immunoprecipitation and fluorescence microscopy in mammalian cells","pmids":["19331828"],"confidence":"High","gaps":["Whether pre-assembly is obligatory or rate-limiting for snoRNP biogenesis"]},{"year":2012,"claim":"High-resolution structural and functional analysis of the Nop56/58 N-terminal domain demonstrated that it mediates an exceptionally stable fibrillarin interaction and directly contacts the target RNA substrate, establishing a catalytic contribution beyond scaffolding.","evidence":"X-ray crystallography (1.7 Å), site-directed mutagenesis, chemical/thermal denaturation, RNA cross-linking, and in vitro methylation assay on archaeal sRNPs","pmids":["22496443"],"confidence":"High","gaps":["Precise residues contacting the substrate RNA not mapped","Whether NTD mutations affect rRNA methylation fidelity in vivo"]},{"year":2013,"claim":"Identifying NOP56 as a rate-limiting target hyperactivated by oncogenic Myc mutants linked snoRNP-mediated rRNA methylation to Myc-driven cell transformation, answering whether ribosome biogenesis components are functionally required for Myc oncogenesis.","evidence":"Gene expression profiling, siRNA knockdown and overexpression with cell transformation and in vivo tumor growth assays","pmids":["24013231"],"confidence":"Medium","gaps":["Which specific rRNA methylation sites are rate-limiting for transformation","Whether NOP56 contributes to transformation independently of its snoRNP role"]},{"year":2018,"claim":"Discovery of a cis-acting autoregulatory feedback loop in which the intron-hosted snoRD86 RNA senses snoRNP core protein levels and switches NOP56 pre-mRNA splicing toward an NMD-destined isoform established a new paradigm for how snoRNP homeostasis is maintained.","evidence":"RNA splicing analysis, NMD pathway assays, RNP structure analysis, and alternative splicing mapping in human cells","pmids":["30220559"],"confidence":"High","gaps":["Whether analogous mechanisms regulate NOP58 or other snoRNP genes","Quantitative contribution of the NMD pathway versus splicing regulation"]},{"year":2021,"claim":"Solving the eukaryotic Nop56 NTD–fibrillarin crystal structure revealed that the methyltransferase recruitment interface has diverged substantially from archaea, answering whether the archaeal structural paradigm generalizes to eukaryotes.","evidence":"High-resolution X-ray crystallography of yeast Nop1–Nop56 NTD complex with structural comparison to archaeal orthologs","pmids":["33483369"],"confidence":"High","gaps":["No full-length eukaryotic box C/D snoRNP structure with guide RNA","How divergent interface relates to differences in eukaryotic snoRNP regulation"]},{"year":2022,"claim":"Zebrafish nop56 loss-of-function demonstrated that NOP56 is essential for vertebrate CNS development, with mutants exhibiting cerebellar agenesis, spinal neuron loss, and high apoptosis, connecting snoRNP function to neuronal survival.","evidence":"Zebrafish genetic knockout with fluorescence microscopy, apoptosis assays, gene expression analysis, and behavioral assays","pmids":["36009362"],"confidence":"Medium","gaps":["Whether neurodegeneration results from global loss of rRNA methylation or specific snoRNA targets","Whether phenotype is cell-autonomous in neurons"]},{"year":2022,"claim":"Demonstrating synthetic lethality between NOP56 depletion and mTOR inhibition in KRAS-mutant lung cancer revealed that NOP56 regulates ROS homeostasis and that cells compensate for NOP56 loss through IRE1α–p38–mTOR signaling.","evidence":"siRNA/shRNA, CRISPR knockout, ROS measurement, Western blot, and xenograft tumor model in KRAS-mutant lung cancer cells","pmids":["35039048"],"confidence":"Medium","gaps":["Whether ROS elevation is a direct consequence of impaired rRNA methylation or a secondary effect","Generalizability beyond KRAS-mutant contexts"]},{"year":2025,"claim":"Characterization of RAN translation from NOP56 GGCCTG intronic repeats showed cap-dependent initiation from near-cognate codons in all sense reading frames with repeat length–dependent enhancement, establishing a molecular mechanism for toxic protein production in NOP56 repeat expansion disease.","evidence":"Cell-free in vitro translation systems with repeat constructs of varying lengths and frameshifting analysis","pmids":["40015643"],"confidence":"Medium","gaps":["Whether RAN translation products accumulate in patient neurons","Relative contribution of RAN products versus RNA toxicity to neurodegeneration","No in vivo validation yet"]},{"year":2026,"claim":"Identification of a NOP56–FBL–PI3K/AKT/CREB signaling axis in hepatocellular carcinoma and a reciprocal NOP56–MYC positive feedback loop in NSCLC extended NOP56's oncogenic roles beyond rRNA methylation to IRES-dependent translation regulation and growth signaling.","evidence":"Co-IP, rescue experiments, ChIP, bisulfite sequencing, luciferase reporters, RNA-seq, and xenograft models in HCC and NSCLC cells","pmids":["41568368","41827688"],"confidence":"Medium","gaps":["Whether the PI3K/AKT activation is a direct consequence of altered ribosome function or a fibrillarin-specific effect","Whether the NOP56–MYC feedback loop operates in non-transformed cells","No structural basis for NOP56's role in IRES-dependent translation"]},{"year":null,"claim":"A complete high-resolution structure of a eukaryotic box C/D snoRNP with NOP56, NOP58, fibrillarin, 15.5K, and guide RNA bound to substrate rRNA is still lacking, and the precise mechanism by which NOP56 contributes to catalysis versus NOP58 within the asymmetric eukaryotic complex remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No full eukaryotic holo-snoRNP structure with substrate","Functional asymmetry between NOP56 and NOP58 not resolved","In vivo identification of NOP56-dependent rRNA methylation sites critical for disease phenotypes"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[0,3,5]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,1,3,6]}],"localization":[{"term_id":"GO:0005730","term_label":"nucleolus","supporting_discovery_ids":[2,4,5]}],"pathway":[{"term_id":"GO:0005730","term_label":"nucleolus","supporting_discovery_ids":[0,3,5]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[0,3,5,6]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,3,6]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[4,8,11,12]}],"complexes":["box C/D snoRNP"],"partners":["FBL","NOP58","NHP2L1","MYC"],"other_free_text":[]},"mechanistic_narrative":"NOP56 is a conserved core subunit of box C/D small nucleolar ribonucleoprotein (snoRNP) complexes essential for 2'-O-methylation of ribosomal RNA and ribosome biogenesis. Its N-terminal domain forms an exceptionally stable interaction with fibrillarin (the methyltransferase catalytic subunit), recruiting it to the guide RNA, while its coiled-coil domain is dispensable for snoRNP assembly but required for proper RNP architecture and guided nucleotide methylation; NOP56 also directly contacts the target RNA substrate, contributing to catalysis beyond a purely scaffolding role [PMID:16601205, PMID:22496443, PMID:33483369]. NOP56 protein levels are autoregulated through an intronic snoRD86-based RNA structure feedback mechanism that couples alternative splicing to nonsense-mediated decay of NOP56 mRNA, and a reciprocal positive feedback loop with MYC links NOP56 to ribosome biogenesis-driven cell transformation and cancer progression [PMID:30220559, PMID:24013231, PMID:41827688]. Loss of NOP56 in zebrafish causes severe cerebellar agenesis and neurodegeneration, and a GGCCTG intronic repeat expansion in NOP56 undergoes repeat-associated non-AUG (RAN) translation in all sense-strand reading frames, connecting NOP56 to neurodegenerative disease mechanisms [PMID:36009362, PMID:40015643]."},"prefetch_data":{"uniprot":{"accession":"O00567","full_name":"Nucleolar protein 56","aliases":["Nucleolar protein 5A"],"length_aa":594,"mass_kda":66.0,"function":"Involved in the early to middle stages of 60S ribosomal subunit biogenesis. Required for the biogenesis of box C/D snoRNAs such U3, U8 and U14 snoRNAs (PubMed:12777385, PubMed:15574333). 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 (PubMed:34516797). Core component of box C/D small nucleolar ribonucleoprotein (snoRNP) complexes that function in methylation of multiple sites on ribosomal RNAs (rRNAs) and messenger RNAs (mRNAs) (PubMed:12777385, PubMed:39570315)","subcellular_location":"Nucleus, nucleolus; Cytoplasm; Nucleus, nucleoplasm","url":"https://www.uniprot.org/uniprotkb/O00567/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/NOP56","classification":"Common Essential","n_dependent_lines":1201,"n_total_lines":1208,"dependency_fraction":0.9942052980132451},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"RAB11A","stoichiometry":10.0},{"gene":"FBL","stoichiometry":4.0},{"gene":"NOP58","stoichiometry":4.0},{"gene":"NCL","stoichiometry":0.2},{"gene":"PSPC1","stoichiometry":0.2},{"gene":"RPS16","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/NOP56","total_profiled":1310},"omim":[{"mim_id":"614155","title":"MICRO RNA 1292; MIR1292","url":"https://www.omim.org/entry/614155"},{"mim_id":"614154","title":"NOP56 RIBONUCLEAR PROTEIN; NOP56","url":"https://www.omim.org/entry/614154"},{"mim_id":"614153","title":"SPINOCEREBELLAR ATAXIA 36; SCA36","url":"https://www.omim.org/entry/614153"},{"mim_id":"614146","title":"DYNEIN, AXONEMAL, ASSEMBLY FACTOR 9; DNAAF9","url":"https://www.omim.org/entry/614146"},{"mim_id":"606847","title":"TREACLE RIBOSOME BIOGENESIS FACTOR 1; TCOF1","url":"https://www.omim.org/entry/606847"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoli fibrillar center","reliability":"Enhanced"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/NOP56"},"hgnc":{"alias_symbol":["SCA36"],"prev_symbol":["NOL5A"]},"alphafold":{"accession":"O00567","domains":[{"cath_id":"3.30.420.220","chopping":"4-158","consensus_level":"high","plddt":85.9999,"start":4,"end":158},{"cath_id":"1.10.287.4070","chopping":"167-282","consensus_level":"high","plddt":88.2122,"start":167,"end":282},{"cath_id":"1.10.246.90","chopping":"295-437","consensus_level":"high","plddt":88.4243,"start":295,"end":437}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O00567","model_url":"https://alphafold.ebi.ac.uk/files/AF-O00567-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O00567-F1-predicted_aligned_error_v6.png","plddt_mean":75.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=NOP56","jax_strain_url":"https://www.jax.org/strain/search?query=NOP56"},"sequence":{"accession":"O00567","fasta_url":"https://rest.uniprot.org/uniprotkb/O00567.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O00567/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O00567"}},"corpus_meta":[{"pmid":"21683323","id":"PMC_21683323","title":"Expansion of intronic GGCCTG hexanucleotide repeat in NOP56 causes SCA36, a type of spinocerebellar ataxia accompanied by motor neuron involvement.","date":"2011","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/21683323","citation_count":214,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"22744658","id":"PMC_22744658","title":"Clinical features of SCA36: a novel spinocerebellar ataxia with motor neuron involvement (Asidan).","date":"2012","source":"Neurology","url":"https://pubmed.ncbi.nlm.nih.gov/22744658","citation_count":72,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"30220559","id":"PMC_30220559","title":"Box C/D snoRNP Autoregulation by a cis-Acting snoRNA in the NOP56 Pre-mRNA.","date":"2018","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/30220559","citation_count":66,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"32375063","id":"PMC_32375063","title":"Chimeric Peptide Species Contribute to Divergent Dipeptide Repeat Pathology in c9ALS/FTD and SCA36.","date":"2020","source":"Neuron","url":"https://pubmed.ncbi.nlm.nih.gov/32375063","citation_count":60,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"24013231","id":"PMC_24013231","title":"Burkitt's lymphoma-associated c-Myc mutations converge on a dramatically altered target gene response and implicate Nol5a/Nop56 in oncogenesis.","date":"2013","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/24013231","citation_count":43,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"32375043","id":"PMC_32375043","title":"Hexanucleotide Repeat Expansions in c9FTD/ALS and SCA36 Confer Selective Patterns of Neurodegeneration In Vivo.","date":"2020","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/32375043","citation_count":38,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"17617422","id":"PMC_17617422","title":"Alternative conformations of the archaeal Nop56/58-fibrillarin complex imply flexibility in box C/D RNPs.","date":"2007","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/17617422","citation_count":30,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"16601205","id":"PMC_16601205","title":"The coiled-coil domain of the Nop56/58 core protein is dispensable for sRNP assembly but is critical for archaeal box C/D sRNP-guided nucleotide methylation.","date":"2006","source":"RNA (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/16601205","citation_count":29,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"29281254","id":"PMC_29281254","title":"Structural and Dynamical Characterization of DNA and RNA Quadruplexes Obtained from the GGGGCC and GGGCCT Hexanucleotide Repeats Associated with C9FTD/ALS and SCA36 Diseases.","date":"2018","source":"ACS chemical 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\"Molecular Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods in single study, mechanistic model with functional validation\",\n      \"pmids\": [\"30220559\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Fibrillarin and NOP56 directly interact in vivo prior to their co-assembly into box C/D snoRNPs; this interaction is mediated by the alpha-helix domain of fibrillarin (not its GAR or RNA-binding domain) and is indispensable for association of both proteins with box C/D snoRNPs.\",\n      \"method\": \"Relocalization/affinity-tag approach in living cells, co-immunoprecipitation, FRAP, fluorescence microscopy\",\n      \"journal\": \"Experimental Cell Research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP plus domain-deletion mapping, live-cell imaging with functional consequence\",\n      \"pmids\": [\"19331828\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"High-resolution crystal structure of eukaryotic (yeast) Nop1 (fibrillarin ortholog) bound to the amino-terminal domain of Nop56 reveals a protein-protein interface that differs substantially from archaeal orthologs, demonstrating that eukaryotic Nop56 recruits the methyltransferase to the box C/D RNP through a distinct, evolutionarily diverged mechanism.\",\n      \"method\": \"X-ray crystallography with functional validation of the interface\",\n      \"journal\": \"RNA\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure with comparative functional analysis\",\n      \"pmids\": [\"33483369\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Crystal structure of the archaeal Nop56/58-fibrillarin complex from Pyrococcus furiosus (with S-adenosyl-L-methionine cofactor) reveals a bipartite symmetric dimer architecture; Nop56/58 adopts a substantially different conformation from the Archaeoglobus fulgidus structure, suggesting hinge-motion flexibility with implications for simultaneously positioning two catalytic sites at two target sites of a bipartite box C/D guide RNA.\",\n      \"method\": \"X-ray crystallography at 2.7 Å; computational normal mode analysis\",\n      \"journal\": \"Journal of Molecular Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with computational validation, confirms general architectural principle\",\n      \"pmids\": [\"17617422\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The coiled-coil domain of archaeal Nop56/58 is dispensable for sRNP assembly and Nop56/58-fibrillarin dimerization, but is critical for sRNP-guided nucleotide 2'-O-methylation; deletion of the coiled-coil domain disrupts box C/D and C'/D' RNP structure essential for methylation. Nop56/58 self-dimerization and Nop56/58-fibrillarin dimerization are mutually exclusive interactions.\",\n      \"method\": \"Site-directed mutagenesis, deletion analysis, protein pull-down, in vitro methylation assay, nuclease probing of sRNP structure\",\n      \"journal\": \"RNA\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with mutagenesis and methylation activity assay\",\n      \"pmids\": [\"16601205\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The N-terminal domain (NTD) of archaeal Nop56/58 mediates an unusually stable interaction with fibrillarin that is essential for both sRNP assembly and 2'-O-methyltransferase activity; NTD mutations that do not prevent fibrillarin binding or sRNP assembly nevertheless disrupt guided nucleotide modification, and Nop56/58 cross-links to the target RNA substrate, revealing a direct role in methyltransferase activity beyond scaffolding.\",\n      \"method\": \"Site-directed mutagenesis, chemical and thermal denaturation, in vitro methylation assay, RNA cross-linking, X-ray crystallography of NTD at 1.7 Å\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure + mutagenesis + in vitro methylation assay + RNA cross-linking in single study\",\n      \"pmids\": [\"22496443\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"NOP56 (Nol5a) is a transcriptional target hyperactivated by Burkitt's lymphoma-associated Myc mutants and is necessary for Myc-induced cell transformation; Nol5a overexpression enhances wild-type Myc-induced transformation and increases tumor size, placing NOP56 downstream of Myc as a rate-limiting factor for oncogenic transformation.\",\n      \"method\": \"Gene expression profiling, RNAi knockdown, colony transformation assay, in vivo tumor growth assay\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function with specific phenotypic readout (transformation) plus gain-of-function, single lab\",\n      \"pmids\": [\"24013231\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"NOP56 depletion in KRAS-mutant lung cancer cells causes elevated ROS and synthetic lethality with mTOR inhibition; mechanistically, reduced NOP56 activates IRE1α-mediated unfolded protein response, which activates mTOR through p38 MAPK to balance oxidative stress, placing NOP56 upstream of the IRE1α-p38 MAPK-mTOR axis in ROS homeostasis.\",\n      \"method\": \"siRNA/shRNA knockdown, CRISPR/Cas9 knockout, flow cytometry (ROS), Western blot, in vivo xenograft, chemical inhibitor screen\",\n      \"journal\": \"Journal of Experimental & Clinical Cancer Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO + pharmacological inhibition + in vivo validation, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"35039048\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Intronic GGCCTG hexanucleotide repeat expansion in NOP56 causes SCA36; expanded repeat RNA forms nuclear RNA foci in patient lymphoblastoid cells, and (GGCCUG)n binds RNA-binding protein SRSF2 (demonstrated by gel-shift assay), suggesting RNA gain-of-function toxicity.\",\n      \"method\": \"Genetic linkage analysis, FISH (RNA foci detection), gel-shift assay\",\n      \"journal\": \"American Journal of Human Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — FISH for foci plus gel-shift for SRSF2 binding, foundational discovery paper\",\n      \"pmids\": [\"21683323\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"The GGCCTG repeat expansion in NOP56 intron 1 undergoes repeat-associated non-AUG (RAN) translation producing poly(GP) and poly(PR) dipeptide repeat proteins; poly(GP) is produced predominantly via canonical AUG-mediated translation from intron-retained repeat RNAs, and chimeric DPR species (not simple DPRs) underlie divergent pathology compared to C9orf72.\",\n      \"method\": \"Immunoassay of patient tissue, RAN translation reporter constructs, mass spectrometry, cell-based translation assays\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — patient tissue analysis plus mechanistic cell-based assays with multiple DPR species characterized\",\n      \"pmids\": [\"32375063\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"NOP56 GGCCUG repeat-associated non-AUG (RAN) translation in cell-free systems occurs in all reading frames of the sense strand; is initiated in a 5'-cap-dependent manner from near-cognate start codons upstream of the repeat; longer repeats enhance RAN translation; and a frameshift occurs within the GGCCUG repeat.\",\n      \"method\": \"Cell-free translation systems, reporter constructs with mutagenesis, in vitro translation assays\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted cell-free system with multiple mechanistic dissections and mutagenesis\",\n      \"pmids\": [\"40015643\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Loss-of-function of nop56 in zebrafish causes severe neurodegeneration characterized by absence of cerebellum, reduced spinal cord neurons, high CNS apoptosis, and impaired movement; nop56 mutants show impaired expression of genes related to the C/D box complex, balance, and CNS development, establishing NOP56 as essential for CNS development and neuronal survival.\",\n      \"method\": \"Zebrafish genetic knockout, fluorescence microscopy, gene expression analysis, behavioral assay\",\n      \"journal\": \"Biomedicines\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean loss-of-function vertebrate model with defined cellular and molecular phenotypes\",\n      \"pmids\": [\"36009362\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"NOP56 forms a G-quadruplex (G4) structure from a 21-nt DNA sequence in intron 1; the antiparallel chair-type G4 contains two G-tetrads and a C·G·C·G tetrad capped by a C·C base pair; the G4 ligand pyridostatin (PDS) binds at the terminal G-tetrad via π-π stacking and electrostatic interactions, increasing melting temperature by ~14°C and significantly reducing NOP56 mRNA levels in cancer cell lines.\",\n      \"method\": \"Solution NMR spectroscopy (high-resolution structure), melting temperature assays, mRNA quantification in cell lines\",\n      \"journal\": \"Advanced Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution NMR structure with functional ligand-binding and gene regulation validation\",\n      \"pmids\": [\"40047221\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"NOP56 interacts with fibrillarin (FBL) in hepatocellular carcinoma cells and activates the PI3K/AKT/CREB signaling pathway; NOP56 knockdown lowers FBL levels and suppresses pathway activity, while FBL overexpression partially rescues apoptotic effects, establishing a NOP56-FBL-PI3K/AKT/CREB axis in HCC.\",\n      \"method\": \"Co-immunoprecipitation, Western blot, siRNA knockdown, xenograft model, FBL rescue experiment\",\n      \"journal\": \"Frontiers in Oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — co-IP plus loss-of-function with rescue, single lab\",\n      \"pmids\": [\"41568368\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"NOP56 activates MYC signaling by regulating IRES-dependent translation, which in turn transcriptionally upregulates NOP56 expression, creating a positive feedback loop; NOP56 promoter hypomethylation also contributes to its upregulation in NSCLC, and NOP56 overexpression promotes ribosome biogenesis, proliferation, and metastasis.\",\n      \"method\": \"Luciferase reporter assay, chromatin immunoprecipitation, bisulfite sequencing, RNA sequencing, Western blot, in vivo xenograft\",\n      \"journal\": \"Cancers\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (ChIP, luciferase, bisulfite seq) in single study\",\n      \"pmids\": [\"41827688\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"During unfolded protein response (UPR), NOP56 expression is significantly downregulated, leading to reduced rRNA 2'-O-methylation and altered translational fidelity including changes in nonsense suppression, frameshifting, ribosome pausing, and IRES-dependent translation initiation.\",\n      \"method\": \"Western blot, siRNA knockdown, rRNA methylation assay, translation fidelity reporters\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — preprint, single lab, expression-level change with downstream functional readouts\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"NOP56 is a core scaffold protein of box C/D snoRNPs that bridges L7Ae/Snu13 and fibrillarin through its N-terminal domain (forming an exceptionally stable heterodimer) and uses its coiled-coil domain to establish proper RNP architecture required for fibrillarin-mediated 2'-O-methylation of ribosomal RNA; its own levels are homeostatically controlled by a cis-acting intronic snoRNA (snoRD86) feedback loop; intronic GGCCTG repeat expansion causes SCA36 through RNA foci formation, SRSF2 sequestration, and RAN translation producing toxic dipeptide repeat proteins via cap-dependent near-cognate initiation with frameshifting; and in cancer contexts NOP56 promotes oncogenesis downstream of Myc by supporting ribosome biogenesis, interacting with fibrillarin to activate PI3K/AKT/CREB signaling, and regulating IRES-dependent MYC translation in a positive feedback loop.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2006,\n      \"finding\": \"The coiled-coil domain of archaeal Nop56/58 is dispensable for sRNP assembly but critical for box C/D sRNP-guided nucleotide methylation. Nop56/58 self-dimerization and Nop56/58-fibrillarin dimerization are mutually exclusive protein-protein interactions. Deletion of the coiled-coil domain disrupts guided methylation from both box C/D and C'/D' RNP complexes and alters RNP structure, despite allowing functional complex assembly.\",\n      \"method\": \"Protein pull-down, site-directed mutagenesis, deletion constructs, in vitro methylation assay, nuclease probing of sRNP structure\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro methylation assay with mutagenesis and structural probing, multiple orthogonal methods\",\n      \"pmids\": [\"16601205\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Crystal structure of the archaeal Nop56/58-fibrillarin complex from Pyrococcus furiosus bound with S-adenosyl-L-methionine reveals a bipartite dimeric arrangement that is a general feature across species. The conformation of Nop56/58 in this structure differs substantially from the earlier Archaeoglobus fulgidus structure, indicating intrinsic conformational flexibility. Computational normal mode analysis supports hinge motion within Nop56/58, suggesting that such flexibility allows simultaneous positioning of two catalytic sites at two target sites of a bipartite box C/D guide RNA.\",\n      \"method\": \"X-ray crystallography (2.7 Å), computational normal mode analysis\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with functional interpretation and computational validation\",\n      \"pmids\": [\"17617422\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Fibrillarin and Nop56 directly interact in vivo before being co-assembled into box C/D snoRNPs. This interaction does not require the glycine- and arginine-rich domain or the RNA-binding domain of fibrillarin, but depends on the alpha-helix domain of fibrillarin. No RNA is required to maintain the fibrillarin-Nop56 interaction. Altering the localization and mobility of core box C/D proteins (including Nop56) impairs their association with box C/D snoRNPs.\",\n      \"method\": \"In vivo relocalization/affinity-tag approach (B23 tag), co-immunoprecipitation, fluorescence microscopy\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal in vivo interaction mapping with domain dissection and multiple orthogonal methods\",\n      \"pmids\": [\"19331828\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The N-terminal domain (NTD) of archaeal Nop56/58 mediates an exceptionally stable interaction with fibrillarin (confirmed by chemical and thermal denaturation). Only deletion of the NTD itself prevented dimerization with fibrillarin. Mutations in the NTD that did not affect fibrillarin binding or sRNP assembly nevertheless disrupted sRNP-guided nucleotide modification, revealing a direct role for Nop56/58 in methyltransferase activity beyond scaffold function. Cross-linking showed Nop56/58 contacts the target RNA substrate. The crystal structure of the Mj Nop56/58 NTD was solved to 1.7 Å, revealing a conserved fold among archaeal homologs despite low primary sequence conservation.\",\n      \"method\": \"Site-directed mutagenesis, chemical/thermal denaturation, in vitro methylation assay, RNA cross-linking, X-ray crystallography (1.7 Å)\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure combined with mutagenesis, methylation assay, and RNA cross-linking in one study\",\n      \"pmids\": [\"22496443\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Nol5a/Nop56 was identified as a gene hyperactivated by Burkitt's lymphoma-associated Myc mutants. Nol5a is required for Myc-induced cell transformation: knockdown reduced transformation, while overexpression enhanced MycWT-induced transformation and increased tumor size. This establishes Nop56 as a rate-limiting nucleolar target gene downstream of Myc that links Myc-induced ribosomal RNA methylation to cell transformation.\",\n      \"method\": \"Gene expression profiling, siRNA knockdown, overexpression, cell transformation assay, in vivo tumor growth assay\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss- and gain-of-function with cellular and in vivo phenotypic readouts, single lab\",\n      \"pmids\": [\"24013231\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The intron-hosted box C/D snoRNA snoRD86 acts in cis as a sensor and master switch controlling levels of the limiting snoRNP core protein NOP56. Excess snoRNP core proteins cause snoRD86 to adopt different RNP conformations that dictate usage of nearby alternative splice donors in the NOP56 pre-mRNA, triggering generation of a cytoplasmic snoRD86-containing NOP56-derived lncRNA via the nonsense-mediated decay (NMD) pathway. This constitutes a feedback mechanism based on RNA structure that coordinates box C/D snoRNP core protein levels and global snoRNA levels.\",\n      \"method\": \"RNA splicing analysis, NMD pathway assays, RNP structure analysis, snoRNA expression measurements, alternative splicing mapping\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal molecular methods establishing feedback mechanism, published in high-impact journal\",\n      \"pmids\": [\"30220559\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"High-resolution crystal structure of eukaryotic (yeast) Nop1 (fibrillarin) bound to the amino-terminal domain of Nop56 reveals the protein-protein interface. The eukaryotic Nop56 NTD recruits the methyltransferase to the box C/D RNP through a protein-protein interface that differs substantially from archaeal orthologs, demonstrating evolutionary divergence in the mechanism of methyltransferase recruitment to the C/D RNP complex.\",\n      \"method\": \"X-ray crystallography (high-resolution structure), structural comparison with archaeal orthologs\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure with functional domain characterization\",\n      \"pmids\": [\"33483369\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Zebrafish nop56 loss-of-function mutants exhibit severe neurodegeneration characterized by absence of cerebellum, reduced numbers of spinal cord neurons, high CNS apoptosis, and impaired movement leading to death before 7 days post-fertilization. Gene expression of genes related to the C/D box complex, balance, and CNS development was impaired in mutants, establishing NOP56 as essential for CNS development and neuronal survival in a vertebrate model.\",\n      \"method\": \"Zebrafish loss-of-function genetic model, fluorescence microscopy, apoptosis assays, gene expression analysis, movement assays\",\n      \"journal\": \"Biomedicines\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean loss-of-function vertebrate model with defined cellular and developmental phenotypes\",\n      \"pmids\": [\"36009362\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"NOP56 depletion causes synthetic lethality with mTOR inhibition in KRAS-mutant lung cancer cells. Mechanistically, NOP56 regulates ROS homeostasis; cells with reduced NOP56 have elevated ROS and rely on mTOR signaling to balance oxidative stress. IRE1α-mediated unfolded protein response (UPR) activates mTOR through p38 MAPK under NOP56 depletion. Co-targeting NOP56 and mTOR profoundly enhances KRAS-mutant tumor cell death in vitro and in vivo.\",\n      \"method\": \"siRNA/shRNA knockdown, CRISPR/Cas9 knockout, flow cytometry (ROS measurement), Western blot, cell viability and apoptosis assays, xenograft tumor model\",\n      \"journal\": \"Journal of experimental & clinical cancer research : CR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic and pharmacological approaches with in vitro and in vivo validation, single lab\",\n      \"pmids\": [\"35039048\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"NOP56 serves as a negative regulator of the MyD88-mediated NF-κB signaling pathway in teleost fish. NOP56 overexpression inhibited MyD88 protein expression, while siRNA knockdown had the opposite effect. The NOSIC domain of NOP56 is responsible for suppressing MyD88 expression at the protein level.\",\n      \"method\": \"Overexpression, siRNA knockdown, Western blot, domain deletion analysis\",\n      \"journal\": \"Fish & shellfish immunology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, non-mammalian model (teleost fish), single method class for domain mapping\",\n      \"pmids\": [\"34774735\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"NOP56 GGCCTG repeat-associated non-AUG (RAN) translation in cell-free systems occurs in all reading frames of the sense strand of NOP56 intron 1. Translation is initiated in a 5' cap-dependent manner from near-cognate start codons upstream of the GGCCUG repeat in each frame. Longer GGCCUG repeats enhance NOP56-RAN translation. A frameshift occurs within the GGCCUG repeat during translation.\",\n      \"method\": \"Cell-free translation systems, in vitro translation assays with repeat constructs of varying lengths, frameshifting analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with cell-free translation systems, mechanistic dissection of RAN translation\",\n      \"pmids\": [\"40015643\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"NOP56 interacts with fibrillarin (FBL) in hepatocellular carcinoma cells and activates the PI3K/AKT/CREB pathway. NOP56 knockdown lowered FBL protein levels and suppressed PI3K/AKT/CREB pathway activity, inducing apoptosis and G0/G1 arrest. FBL overexpression partially rescued apoptotic effects of NOP56 silencing, establishing a NOP56-FBL-PI3K/AKT/CREB signaling axis in HCC.\",\n      \"method\": \"Co-immunoprecipitation, Western blot, siRNA knockdown, overexpression, xenograft tumor model, flow cytometry\",\n      \"journal\": \"Frontiers in oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP plus rescue experiment with pathway analysis, single lab\",\n      \"pmids\": [\"41568368\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"NOP56 activates MYC signaling by regulating IRES-dependent translation, which in turn transcriptionally upregulates NOP56 expression creating a positive feedback loop. NOP56 overexpression promotes ribosome biogenesis, cellular proliferation, and metastasis in non-small cell lung cancer. Hypomethylation of the NOP56 promoter contributes to its upregulation in NSCLC.\",\n      \"method\": \"RNA sequencing, qPCR, Western blot, luciferase reporter assay, chromatin immunoprecipitation (ChIP), bisulfite DNA sequencing, functional assays, in vivo tumor model\",\n      \"journal\": \"Cancers\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (ChIP, bisulfite sequencing, luciferase, RNA-seq) establishing feedback mechanism, single lab\",\n      \"pmids\": [\"41827688\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"UPR (unfolded protein response) activation significantly downregulates NOP56 expression along with other C/D box snoRNP core proteins (NHP2L1 and FBL). Reduced C/D box snoRNP function during UPR alters rRNA methylation and translational fidelity, including changes in nonsense suppression, frameshifting, ribosome pausing, and IRES-dependent translation initiation.\",\n      \"method\": \"qPCR/Western blot for expression, rRNA methylation assay, translational fidelity reporter assays (nonsense suppression, frameshift, IRES reporters), UPR induction\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — preprint, single lab, NOP56 downregulation shown but mechanistic role attributed to collective snoRNP reduction\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"NOP56 is a conserved core component of box C/D snoRNP complexes that directly interacts with fibrillarin (through its N-terminal domain) and with the guide snoRNA to scaffold and facilitate 2'-O-methylation of rRNA nucleotides; its coiled-coil domain is required for proper RNP architecture and methyltransferase activity, its levels are autoregulated by a cis-acting snoRD86-based RNA structure feedback mechanism in the NOP56 pre-mRNA, and in cancer contexts NOP56 promotes ribosome biogenesis and cell transformation downstream of MYC while also regulating ROS homeostasis and mTOR-dependent survival signaling.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"NOP56 is a core structural and functional component of eukaryotic box C/D small nucleolar ribonucleoprotein (snoRNP) complexes that catalyze 2'-O-methylation of ribosomal RNA, and its dysfunction is linked to both neurodegeneration and oncogenesis. The N-terminal domain of NOP56 forms an exceptionally stable heterodimer with fibrillarin (the methyltransferase subunit), recruiting it to the snoRNP through an evolutionarily diverged protein interface, while the coiled-coil domain is dispensable for assembly but essential for establishing the RNP architecture required for guided methylation [PMID:16601205, PMID:22496443, PMID:33483369]. NOP56 protein levels are homeostatically regulated by its intron-hosted snoRNA snoRD86, which senses snoRNP core protein abundance and triggers alternative splicing coupled to nonsense-mediated decay [PMID:30220559]. Intronic GGCCTG hexanucleotide repeat expansion in NOP56 causes spinocerebellar ataxia type 36 (SCA36) through RNA foci formation, sequestration of SRSF2, and cap-dependent RAN translation producing toxic dipeptide repeat proteins [PMID:21683323, PMID:32375063, PMID:40015643].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Defining the domain architecture of the Nop56/58–fibrillarin complex resolved how the coiled-coil domain contributes to methylation without being required for assembly, establishing that the sRNP catalytic architecture depends on more than simple scaffolding.\",\n      \"evidence\": \"Deletion mutagenesis, protein pull-downs, in vitro methylation, and nuclease probing of archaeal sRNPs\",\n      \"pmids\": [\"16601205\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Exact mechanism by which coiled-coil domain organizes substrate RNA for methylation is unresolved\",\n        \"Eukaryotic NOP56 and NOP58 may have diverged functions not captured by the archaeal single-gene system\"\n      ]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Crystallographic determination of the archaeal Nop56/58–fibrillarin dimer revealed hinge-motion flexibility, suggesting how two catalytic sites could simultaneously engage bipartite guide RNA substrates.\",\n      \"evidence\": \"X-ray crystallography at 2.7 Å of P. furiosus complex with SAM cofactor, plus computational normal mode analysis\",\n      \"pmids\": [\"17617422\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structure is archaeal; eukaryotic complex architecture remained unknown\",\n        \"Functional significance of hinge motion not directly tested\"\n      ]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstrating that fibrillarin and NOP56 interact in vivo prior to snoRNP assembly, mediated by fibrillarin's alpha-helix domain, established the order of events in eukaryotic box C/D snoRNP biogenesis.\",\n      \"evidence\": \"Relocalization/affinity-tag approach, reciprocal co-IP, and FRAP in living human cells\",\n      \"pmids\": [\"19331828\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Chaperones or assembly factors that facilitate the NOP56–fibrillarin pre-complex were not identified\",\n        \"Whether NOP56 and NOP58 compete for fibrillarin binding in vivo was not addressed\"\n      ]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identification of the GGCCTG repeat expansion in NOP56 intron 1 as the cause of SCA36, with RNA foci and SRSF2 sequestration, established the first disease mechanism for this gene and pointed to RNA gain-of-function toxicity.\",\n      \"evidence\": \"Genetic linkage in Japanese families, FISH for RNA foci in patient lymphoblastoid cells, gel-shift assay for SRSF2 binding\",\n      \"pmids\": [\"21683323\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether NOP56 protein loss-of-function contributes to SCA36 in addition to RNA toxicity was unclear\",\n        \"Downstream consequences of SRSF2 sequestration on splicing not characterized\",\n        \"No animal model established in this study\"\n      ]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"The N-terminal domain of Nop56/58 was shown to do more than scaffold fibrillarin — specific NTD mutations disrupted methyltransferase activity without preventing assembly, and NOP56/58 cross-linked directly to substrate RNA, revealing a catalytic participation role.\",\n      \"evidence\": \"Crystal structure of NTD at 1.7 Å, site-directed mutagenesis, in vitro methylation assay, and RNA cross-linking in archaeal system\",\n      \"pmids\": [\"22496443\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Precise catalytic contribution (allosteric activation vs. substrate positioning) not distinguished\",\n        \"Whether eukaryotic NOP56 NTD functions identically was not tested\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Positioning NOP56 as a direct Myc transcriptional target required for oncogenic transformation linked ribosome biogenesis to cancer through a specific effector gene rather than through general ribosome output.\",\n      \"evidence\": \"Gene expression profiling, RNAi knockdown, colony transformation assay, and in vivo tumor growth in Burkitt's lymphoma model\",\n      \"pmids\": [\"24013231\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether NOP56's oncogenic role is through snoRNP function, ribosome biogenesis, or another mechanism was not resolved\",\n        \"Single lab finding; generality across cancer types not established at the time\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Discovery of the snoRD86-mediated autoregulatory feedback loop revealed how NOP56 protein homeostasis is maintained: excess snoRNP core proteins alter snoRD86 RNP conformations to trigger alternative splicing and NMD of NOP56 mRNA.\",\n      \"evidence\": \"Alternative splicing reporters, NMD pathway manipulation, RNA structure probing, and functional rescue in human cells\",\n      \"pmids\": [\"30220559\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether analogous feedback loops exist for NOP58 or fibrillarin was not determined\",\n        \"Structural basis of how different RNP conformations direct splice-site choice is unresolved\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Detection of RAN translation products (poly-GP and poly-PR dipeptide repeat proteins) from the NOP56 repeat expansion in patient tissue established a second toxic mechanism beyond RNA foci in SCA36, with chimeric DPR species distinguishing it from C9orf72 pathology.\",\n      \"evidence\": \"Immunoassay of patient tissue, RAN translation reporters, mass spectrometry, and cell-based translation assays\",\n      \"pmids\": [\"32375063\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Relative contributions of RNA foci vs. DPR toxicity to SCA36 neurodegeneration unresolved\",\n        \"Whether poly-PR has the same toxicity profile as C9orf72-derived poly-PR not tested\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Solving the eukaryotic (yeast) Nop1–Nop56 NTD crystal structure revealed a protein interface substantially different from archaea, establishing that eukaryotic snoRNP architecture evolved a distinct methyltransferase recruitment mechanism.\",\n      \"evidence\": \"X-ray crystallography with functional validation of the interface\",\n      \"pmids\": [\"33483369\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Human NOP56–fibrillarin interface structure remains unsolved\",\n        \"Whether the eukaryotic-specific interface enables regulation absent in archaea is unknown\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Two studies expanded understanding of NOP56's biological roles: zebrafish nop56 knockout demonstrated essential requirement for cerebellar development and neuronal survival, while NOP56 depletion in KRAS-mutant cancer cells revealed synthetic lethality with mTOR inhibition through IRE1α-p38 MAPK-mediated ROS homeostasis.\",\n      \"evidence\": \"Zebrafish knockout with developmental and behavioral phenotyping; siRNA/shRNA/CRISPR in lung cancer cells with chemical inhibitor screen and xenograft\",\n      \"pmids\": [\"36009362\", \"35039048\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether zebrafish neurodegeneration reflects snoRNP-dependent or snoRNP-independent NOP56 functions is unknown\",\n        \"Synthetic lethality with mTOR inhibitors not validated in clinical setting\",\n        \"Connection between rRNA methylation loss and UPR/ROS axis not mechanistically dissected\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Cell-free reconstitution of RAN translation from GGCCUG repeats established that it is 5'-cap-dependent, initiated from near-cognate start codons upstream of the repeat, occurs in all sense reading frames, and involves frameshifting within the repeat — mechanistically distinguishing it from purely repeat-length-dependent RAN translation models.\",\n      \"evidence\": \"Cell-free translation systems with reporter constructs, start codon mutagenesis, and in vitro translation\",\n      \"pmids\": [\"40015643\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether the same initiation mechanism operates in neurons in vivo is untested\",\n        \"Antisense strand RAN translation not addressed\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"An intronic G-quadruplex structure in NOP56 was solved by NMR, and its stabilization by pyridostatin reduced NOP56 mRNA levels, suggesting a pharmacological strategy to modulate NOP56 expression.\",\n      \"evidence\": \"Solution NMR spectroscopy, melting temperature assays, mRNA quantification in cancer cell lines\",\n      \"pmids\": [\"40047221\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Selectivity of G4 ligands for NOP56 versus other G4-containing genes not assessed\",\n        \"In vivo efficacy and therapeutic window not established\"\n      ]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Two cancer studies expanded the oncogenic mechanism: NOP56 interacts with fibrillarin to activate PI3K/AKT/CREB signaling in hepatocellular carcinoma, and NOP56 promotes IRES-dependent MYC translation creating a NOP56-MYC positive feedback loop in NSCLC, with promoter hypomethylation contributing to NOP56 upregulation.\",\n      \"evidence\": \"Co-IP, Western blot, siRNA, xenograft, FBL rescue in HCC; luciferase reporters, ChIP, bisulfite sequencing, RNA-seq in NSCLC\",\n      \"pmids\": [\"41568368\", \"41827688\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether PI3K/AKT activation is a direct consequence of altered rRNA methylation or a fibrillarin-specific function is unclear\",\n        \"The NOP56-MYC feedback loop has not been validated outside NSCLC\",\n        \"Both studies from single labs; independent replication pending\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions include: the structural basis of the human NOP56–fibrillarin–snoRNA ternary complex; the relative pathogenic contributions of RNA foci, SRSF2 sequestration, and DPR toxicity in SCA36; whether NOP56's oncogenic functions are primarily through ribosome biogenesis or through non-canonical signaling; and the therapeutic potential of G4-targeting or antisense approaches to modulate NOP56.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No high-resolution structure of the full human box C/D snoRNP with NOP56\",\n        \"No animal model of SCA36 with dissection of individual toxic mechanisms\",\n        \"Causal relationship between rRNA 2'-O-methylation changes and oncogenic signaling not established\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [4, 5]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [1, 2, 3, 4, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [1, 4, 5]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [0, 4, 5]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [2, 3, 5]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [6, 7, 8, 9, 13, 14]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [7, 13]}\n    ],\n    \"complexes\": [\n      \"box C/D snoRNP\"\n    ],\n    \"partners\": [\n      \"FBL\",\n      \"SRSF2\",\n      \"SNU13\",\n      \"NOP58\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"NOP56 is a conserved core subunit of box C/D small nucleolar ribonucleoprotein (snoRNP) complexes essential for 2'-O-methylation of ribosomal RNA and ribosome biogenesis. Its N-terminal domain forms an exceptionally stable interaction with fibrillarin (the methyltransferase catalytic subunit), recruiting it to the guide RNA, while its coiled-coil domain is dispensable for snoRNP assembly but required for proper RNP architecture and guided nucleotide methylation; NOP56 also directly contacts the target RNA substrate, contributing to catalysis beyond a purely scaffolding role [PMID:16601205, PMID:22496443, PMID:33483369]. NOP56 protein levels are autoregulated through an intronic snoRD86-based RNA structure feedback mechanism that couples alternative splicing to nonsense-mediated decay of NOP56 mRNA, and a reciprocal positive feedback loop with MYC links NOP56 to ribosome biogenesis-driven cell transformation and cancer progression [PMID:30220559, PMID:24013231, PMID:41827688]. Loss of NOP56 in zebrafish causes severe cerebellar agenesis and neurodegeneration, and a GGCCTG intronic repeat expansion in NOP56 undergoes repeat-associated non-AUG (RAN) translation in all sense-strand reading frames, connecting NOP56 to neurodegenerative disease mechanisms [PMID:36009362, PMID:40015643].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Determining whether the coiled-coil domain of Nop56/58 functions in snoRNP assembly or catalysis resolved its role: the domain is dispensable for RNP formation but essential for guided 2'-O-methylation and proper RNP architecture, and Nop56/58 self-dimerization and fibrillarin binding are mutually exclusive.\",\n      \"evidence\": \"In vitro methylation assays with deletion/mutation constructs and nuclease probing of archaeal sRNPs\",\n      \"pmids\": [\"16601205\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the coiled-coil requirement is conserved in eukaryotic NOP56\", \"Mechanism by which coiled-coil domain organizes dual catalytic sites\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Solving the crystal structure of the archaeal Nop56/58–fibrillarin–SAM complex revealed a bipartite dimeric arrangement with intrinsic conformational flexibility, explaining how two catalytic sites can be positioned on a single bipartite C/D guide RNA.\",\n      \"evidence\": \"X-ray crystallography (2.7 Å) of Pyrococcus furiosus complex plus computational normal mode analysis\",\n      \"pmids\": [\"17617422\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No eukaryotic structure available at the time\", \"Structural basis of substrate RNA engagement unresolved\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"In vivo interaction mapping established that fibrillarin and Nop56 form a pre-assembled heterodimer before incorporation into box C/D snoRNPs, with the fibrillarin α-helix domain but not its GAR or RNA-binding domains mediating the interaction.\",\n      \"evidence\": \"In vivo relocalization/affinity-tag approach with co-immunoprecipitation and fluorescence microscopy in mammalian cells\",\n      \"pmids\": [\"19331828\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether pre-assembly is obligatory or rate-limiting for snoRNP biogenesis\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"High-resolution structural and functional analysis of the Nop56/58 N-terminal domain demonstrated that it mediates an exceptionally stable fibrillarin interaction and directly contacts the target RNA substrate, establishing a catalytic contribution beyond scaffolding.\",\n      \"evidence\": \"X-ray crystallography (1.7 Å), site-directed mutagenesis, chemical/thermal denaturation, RNA cross-linking, and in vitro methylation assay on archaeal sRNPs\",\n      \"pmids\": [\"22496443\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise residues contacting the substrate RNA not mapped\", \"Whether NTD mutations affect rRNA methylation fidelity in vivo\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identifying NOP56 as a rate-limiting target hyperactivated by oncogenic Myc mutants linked snoRNP-mediated rRNA methylation to Myc-driven cell transformation, answering whether ribosome biogenesis components are functionally required for Myc oncogenesis.\",\n      \"evidence\": \"Gene expression profiling, siRNA knockdown and overexpression with cell transformation and in vivo tumor growth assays\",\n      \"pmids\": [\"24013231\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Which specific rRNA methylation sites are rate-limiting for transformation\", \"Whether NOP56 contributes to transformation independently of its snoRNP role\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Discovery of a cis-acting autoregulatory feedback loop in which the intron-hosted snoRD86 RNA senses snoRNP core protein levels and switches NOP56 pre-mRNA splicing toward an NMD-destined isoform established a new paradigm for how snoRNP homeostasis is maintained.\",\n      \"evidence\": \"RNA splicing analysis, NMD pathway assays, RNP structure analysis, and alternative splicing mapping in human cells\",\n      \"pmids\": [\"30220559\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether analogous mechanisms regulate NOP58 or other snoRNP genes\", \"Quantitative contribution of the NMD pathway versus splicing regulation\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Solving the eukaryotic Nop56 NTD–fibrillarin crystal structure revealed that the methyltransferase recruitment interface has diverged substantially from archaea, answering whether the archaeal structural paradigm generalizes to eukaryotes.\",\n      \"evidence\": \"High-resolution X-ray crystallography of yeast Nop1–Nop56 NTD complex with structural comparison to archaeal orthologs\",\n      \"pmids\": [\"33483369\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No full-length eukaryotic box C/D snoRNP structure with guide RNA\", \"How divergent interface relates to differences in eukaryotic snoRNP regulation\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Zebrafish nop56 loss-of-function demonstrated that NOP56 is essential for vertebrate CNS development, with mutants exhibiting cerebellar agenesis, spinal neuron loss, and high apoptosis, connecting snoRNP function to neuronal survival.\",\n      \"evidence\": \"Zebrafish genetic knockout with fluorescence microscopy, apoptosis assays, gene expression analysis, and behavioral assays\",\n      \"pmids\": [\"36009362\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether neurodegeneration results from global loss of rRNA methylation or specific snoRNA targets\", \"Whether phenotype is cell-autonomous in neurons\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrating synthetic lethality between NOP56 depletion and mTOR inhibition in KRAS-mutant lung cancer revealed that NOP56 regulates ROS homeostasis and that cells compensate for NOP56 loss through IRE1α–p38–mTOR signaling.\",\n      \"evidence\": \"siRNA/shRNA, CRISPR knockout, ROS measurement, Western blot, and xenograft tumor model in KRAS-mutant lung cancer cells\",\n      \"pmids\": [\"35039048\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether ROS elevation is a direct consequence of impaired rRNA methylation or a secondary effect\", \"Generalizability beyond KRAS-mutant contexts\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Characterization of RAN translation from NOP56 GGCCTG intronic repeats showed cap-dependent initiation from near-cognate codons in all sense reading frames with repeat length–dependent enhancement, establishing a molecular mechanism for toxic protein production in NOP56 repeat expansion disease.\",\n      \"evidence\": \"Cell-free in vitro translation systems with repeat constructs of varying lengths and frameshifting analysis\",\n      \"pmids\": [\"40015643\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether RAN translation products accumulate in patient neurons\", \"Relative contribution of RAN products versus RNA toxicity to neurodegeneration\", \"No in vivo validation yet\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Identification of a NOP56–FBL–PI3K/AKT/CREB signaling axis in hepatocellular carcinoma and a reciprocal NOP56–MYC positive feedback loop in NSCLC extended NOP56's oncogenic roles beyond rRNA methylation to IRES-dependent translation regulation and growth signaling.\",\n      \"evidence\": \"Co-IP, rescue experiments, ChIP, bisulfite sequencing, luciferase reporters, RNA-seq, and xenograft models in HCC and NSCLC cells\",\n      \"pmids\": [\"41568368\", \"41827688\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether the PI3K/AKT activation is a direct consequence of altered ribosome function or a fibrillarin-specific effect\", \"Whether the NOP56–MYC feedback loop operates in non-transformed cells\", \"No structural basis for NOP56's role in IRES-dependent translation\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A complete high-resolution structure of a eukaryotic box C/D snoRNP with NOP56, NOP58, fibrillarin, 15.5K, and guide RNA bound to substrate rRNA is still lacking, and the precise mechanism by which NOP56 contributes to catalysis versus NOP58 within the asymmetric eukaryotic complex remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No full eukaryotic holo-snoRNP structure with substrate\", \"Functional asymmetry between NOP56 and NOP58 not resolved\", \"In vivo identification of NOP56-dependent rRNA methylation sites critical for disease phenotypes\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [0, 3, 5]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 1, 3, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [2, 4, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [0, 3, 5]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [0, 3, 5, 6]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 3, 6]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [4, 8, 11, 12]}\n    ],\n    \"complexes\": [\n      \"box C/D snoRNP\"\n    ],\n    \"partners\": [\n      \"FBL\",\n      \"NOP58\",\n      \"NHP2L1\",\n      \"MYC\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}