{"gene":"POP7","run_date":"2026-04-28T19:45:44","timeline":{"discoveries":[{"year":2007,"finding":"Pop6 and Pop7 (yeast orthologs of human Rpp25 and Rpp20) form a soluble heterodimer that binds the P3 domain of both RNase MRP and RNase P RNAs. Footprint analysis showed the Pop6/7 complex binds a conserved region of the P3 domain and induces local structural rearrangement of the P3 loop, suggesting it mediates binding of other protein components.","method":"Bacterial expression of recombinant proteins, gel mobility shift assays, RNA footprint analysis","journal":"RNA (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1-2 — reconstituted heterodimer, footprinting, gel shift; multiple orthogonal methods in single study","pmids":["17717080"],"is_preprint":false},{"year":1998,"finding":"Rpp2 (yeast ortholog of human POP7/Rpp20) is a protein subunit of nuclear RNase P and RNase MRP; depletion of Rpp2 in vivo causes accumulation of precursor tRNAs with unprocessed introns and 5'/3' termini, and defects in processing of 35S precursor rRNA and 5.8S rRNA. Rpp2 immunoprecipitates cleave precursor tRNAs and rRNAs at expected sites and co-associate with the Rpp1 protein (ortholog of human Rpp30).","method":"Epitope-tagged immunoprecipitation, in vivo depletion, in vitro cleavage assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP, in vivo depletion with defined phenotypic readout, in vitro cleavage assay","pmids":["9618478"],"is_preprint":false},{"year":2006,"finding":"Human Rpp20 (POP7 ortholog) and Rpp25 form a salt- and detergent-resistant heterodimer; heterodimerization strongly enhances their interaction with the P3 domain of RNase MRP RNA. Only a single copy of each protein associates with RNase MRP/P particles. Nucleolar accumulation of Rpp20 is strongly dependent on its interaction with Rpp25. Knockdown and overexpression experiments show their expression levels are codependent.","method":"Co-immunoprecipitation, gel filtration, RNA binding assays, immunofluorescence, knockdown/overexpression","journal":"RNA (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (co-IP, localization, KD/OE, RNA binding), replicated in human cells","pmids":["17119099"],"is_preprint":false},{"year":2010,"finding":"Human Rpp20 and Rpp25 individually bind the P3 arm of RNase MRP RNA with negligible affinity, but the 1:1 Rpp20:Rpp25 heterodimer binds the same target with nM affinity, establishing that heterodimer formation is a prerequisite for RNA recognition. Deletion analysis mapped the Alba-type core domain of both proteins as containing the key determinants for mutual association and P3 RNA binding.","method":"In vitro binding assays, biophysical characterization (CD, ITC/SPR implied), deletion mutagenesis","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 — quantitative in vitro reconstitution with mutagenesis, unambiguous demonstration of cooperativity","pmids":["20215441"],"is_preprint":false},{"year":2004,"finding":"Human Rpp20 (POP7) interacts with SMN protein; the interaction was identified by yeast two-hybrid and validated by in vitro binding assays and co-immunoprecipitation. Exons 3-4 of SMN are necessary and sufficient for Rpp20 binding. In response to stress, SMN aggregates and redistributes Rpp20 from a diffuse nuclear/cytoplasmic distribution into punctuated cytoplasmic SMN granules.","method":"Yeast two-hybrid, in vitro binding assay, co-immunoprecipitation, immunofluorescence","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2-3 — multiple methods (Y2H, in vitro binding, co-IP, IF) but single lab and interaction domain mapped only on SMN side","pmids":["14715275"],"is_preprint":false},{"year":2018,"finding":"Crystal structure of the human Rpp20/Rpp25 (POP7/Rpp25) heterodimer was determined, revealing quaternary-level differences from archaeal Alba homodimers as the structural basis for adaptation to single-stranded RNA binding specificity in the P3 internal loop of RNase P/MRP.","method":"X-ray crystallography, comparative structural analysis","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with comparative functional interpretation","pmids":["29625199"],"is_preprint":false},{"year":2021,"finding":"Crystal structure of human RPP20-RPP25 (POP7-Rpp25) in complex with the P3 domain of lncRNA RMRP was determined; RPP20-RPP25 binds P3 RNA via a conserved positively-charged surface interacting with the distal stem and internal loop regions of P3. Disease-related RMRP mutations cluster at the protein-RNA interface. The structure also reveals a homodimeric organization of the entire RPP20-RPP25-RMRP P3 complex, suggesting dimerization of human RNase MRP complex in cells.","method":"X-ray crystallography","journal":"Journal of structural biology","confidence":"High","confidence_rationale":"Tier 1 — crystal structure of ternary complex with disease-mutation mapping at interface","pmids":["33571640"],"is_preprint":false},{"year":2009,"finding":"Crystals of a complex containing the P3 RNA domain of yeast RNase MRP with Pop6 and Pop7 proteins were obtained and diffracted to 3.25 Å, enabling structural analysis of how these proteins interact with the P3 RNA.","method":"X-ray crystallography (crystallization and preliminary diffraction)","journal":"Acta crystallographica. Section F, Structural biology and crystallization communications","confidence":"Medium","confidence_rationale":"Tier 1 method but only preliminary crystallographic data reported, no refined structure","pmids":["20057077"],"is_preprint":false},{"year":2022,"finding":"Human POP7 binds preferentially to intron regions of mRNAs (identified by RIP-seq) and promotes breast cancer progression by stabilizing ILF3 mRNA; knockdown of ILF3 impaired the malignant phenotypes conferred by POP7 overexpression, placing POP7 upstream of ILF3 in this pathway.","method":"RNA immunoprecipitation sequencing (RIP-seq), mRNA stability assay, knockdown/overexpression with functional readouts (proliferation, invasion, in vivo tumor growth)","journal":"Cancer science","confidence":"Medium","confidence_rationale":"Tier 2-3 — RIP-seq plus epistasis by knockdown, single lab study","pmids":["35579257"],"is_preprint":false}],"current_model":"POP7 (human Rpp20/yeast Rpp2) is a subunit of both RNase P and RNase MRP that obligatorily heterodimerizes with Rpp25 (Pop6 in yeast) to form a complex that binds the P3 RNA domain of these ribonucleases with nM affinity, a interaction structurally mediated by a conserved positively-charged surface of the heterodimer and required for catalytic activity (tRNA 5' leader removal and rRNA processing); the heterodimer also regulates nucleolar localization and protein stability of both subunits, and has been found to interact with SMN and to regulate ILF3 mRNA stability in cancer cells."},"narrative":{"teleology":[{"year":1998,"claim":"Establishing POP7 (Rpp2) as an essential subunit of both RNase P and RNase MRP resolved that the same protein participates in tRNA 5'-end processing and pre-rRNA maturation.","evidence":"Epitope-tagged immunoprecipitation, in vivo depletion, and in vitro cleavage assays in yeast","pmids":["9618478"],"confidence":"High","gaps":["Mechanism by which Rpp2 contributes to catalysis was unknown","Direct RNA-binding site not identified","Physical partners within the holoenzyme not mapped"]},{"year":2004,"claim":"Identification of SMN as a physical interaction partner of POP7 raised the possibility that RNase P/MRP components participate in stress-granule biology or SMN-dependent pathways.","evidence":"Yeast two-hybrid, in vitro binding, co-immunoprecipitation, and immunofluorescence in human cells","pmids":["14715275"],"confidence":"Medium","gaps":["Interaction mapped only on the SMN side (exons 3–4); POP7 binding determinants undefined","Functional consequence of POP7–SMN interaction not established","Not independently replicated"]},{"year":2006,"claim":"Demonstrating that Rpp20 and Rpp25 form a stable obligate heterodimer whose assembly is prerequisite for P3 RNA binding and nucleolar localization explained how two individually weak RNA-binding proteins achieve high-affinity recognition and co-regulate each other's stability.","evidence":"Co-immunoprecipitation, gel filtration, RNA binding assays, immunofluorescence, knockdown/overexpression in human cells","pmids":["17119099"],"confidence":"High","gaps":["Structural basis of heterodimerization unknown","Whether dimerization is sufficient for holoenzyme assembly not tested"]},{"year":2007,"claim":"Footprinting of the yeast Pop6–Pop7 complex on P3 RNA revealed that the heterodimer induces local structural rearrangement of the P3 loop, suggesting it primes the RNA for recruitment of additional protein subunits.","evidence":"Recombinant protein expression, gel mobility shift, RNA footprinting in vitro","pmids":["17717080"],"confidence":"High","gaps":["Identity of subsequently recruited subunits not determined","No atomic-resolution view of the RNA conformational change"]},{"year":2010,"claim":"Quantitative binding measurements and deletion mutagenesis pinpointed the Alba-type core domains as the minimal determinants for both heterodimerization and cooperative nM-affinity P3 RNA binding, definitively establishing cooperativity as the mechanism underlying RNA recognition.","evidence":"In vitro binding assays with deletion mutants, biophysical characterization","pmids":["20215441"],"confidence":"High","gaps":["No structure of the RNA-bound complex","Contributions of regions outside the Alba core not fully resolved"]},{"year":2018,"claim":"The crystal structure of the free Rpp20–Rpp25 heterodimer revealed how quaternary-level divergence from archaeal Alba homodimers adapted the complex for single-stranded RNA recognition in the P3 internal loop.","evidence":"X-ray crystallography with comparative structural analysis","pmids":["29625199"],"confidence":"High","gaps":["Structure lacked bound RNA, so the RNA-recognition interface was inferred rather than observed"]},{"year":2021,"claim":"The co-crystal structure of RPP20–RPP25 with the RMRP P3 domain provided the first atomic view of the protein–RNA interface, showing that a conserved positively charged surface contacts the distal stem and internal loop, and that cartilage-hair hypoplasia RMRP mutations cluster at this interface.","evidence":"X-ray crystallography of the ternary complex","pmids":["33571640"],"confidence":"High","gaps":["Homodimeric organization of the ternary complex awaits validation in the context of the full holoenzyme","Functional impact of individual interface mutations not tested by mutagenesis-activity assays"]},{"year":2022,"claim":"Discovery that POP7 binds mRNA introns and stabilizes ILF3 mRNA to promote breast cancer progression expanded its functional repertoire beyond canonical RNase P/MRP activities.","evidence":"RIP-seq, mRNA stability assays, knockdown/overexpression with proliferation and invasion readouts in breast cancer cells and xenografts","pmids":["35579257"],"confidence":"Medium","gaps":["Mechanism of mRNA stabilization not defined (direct vs. indirect)","Single-lab finding; not independently replicated","Relationship between RNase MRP function and mRNA stabilization role unclear"]},{"year":null,"claim":"How POP7–Rpp25 heterodimer assembly integrates into full RNase P and RNase MRP holoenzyme architecture and catalytic mechanism in human cells remains unresolved, as does the physiological significance of the SMN interaction and the non-canonical mRNA-stabilizing activity.","evidence":"","pmids":[],"confidence":"High","gaps":["No cryo-EM or crystal structure of the complete human RNase P or MRP holoenzyme with POP7 positioned","SMN interaction has no established functional consequence","mRNA stabilization mechanism and its relationship to canonical ribonuclease function are undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[0,2,3,6,8]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,2,5,6]}],"localization":[{"term_id":"GO:0005730","term_label":"nucleolus","supporting_discovery_ids":[2]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[2,4]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[1,0,3,6]}],"complexes":["RNase P","RNase MRP"],"partners":["RPP25","RPP30","SMN1"],"other_free_text":[]},"mechanistic_narrative":"POP7 (also known as Rpp20; yeast ortholog Rpp2/Pop7) is an obligate subunit of both RNase P and RNase MRP ribonucleoprotein complexes, where it functions in tRNA 5'-leader processing and pre-rRNA maturation. POP7 forms a salt-resistant heterodimer with Rpp25 (Pop6 in yeast) through their conserved Alba-type core domains; neither subunit alone binds the P3 RNA domain of RNase MRP/P with appreciable affinity, but the 1:1 heterodimer engages the P3 internal loop and distal stem via a conserved positively charged surface with nanomolar affinity, and this interaction is required for catalytic activity and nucleolar localization [PMID:17717080, PMID:20215441, PMID:33571640]. Crystal structures of the free heterodimer and its ternary complex with the RMRP P3 domain reveal quaternary-level divergence from archaeal Alba homodimers that underlies single-stranded RNA recognition specificity, and show that disease-causing RMRP mutations cluster at the protein–RNA interface [PMID:29625199, PMID:33571640]. Beyond its canonical ribonuclease roles, POP7 binds intronic regions of mRNAs and stabilizes ILF3 mRNA to promote breast cancer cell proliferation and invasion [PMID:35579257]."},"prefetch_data":{"uniprot":{"accession":"O75817","full_name":"Ribonuclease P protein subunit p20","aliases":["Ribonucleases P/MRP protein subunit POP7 homolog","hPOP7"],"length_aa":140,"mass_kda":15.7,"function":"Component of ribonuclease P, a ribonucleoprotein complex that generates mature tRNA molecules by cleaving their 5'-ends (PubMed:30454648, PubMed:9630247). Also a component of the MRP ribonuclease complex, which cleaves pre-rRNA sequences (PubMed:28115465)","subcellular_location":"Nucleus, nucleolus; Cytoplasm; Cytoplasmic granule","url":"https://www.uniprot.org/uniprotkb/O75817/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/POP7","classification":"Common Essential","n_dependent_lines":960,"n_total_lines":1208,"dependency_fraction":0.7947019867549668},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"RPP30","stoichiometry":10.0},{"gene":"RACK1","stoichiometry":0.2},{"gene":"RBM8A","stoichiometry":0.2},{"gene":"RPS16","stoichiometry":0.2},{"gene":"SSB","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/POP7","total_profiled":1310},"omim":[{"mim_id":"619235","title":"RIBONUCLEASE P/MRP SUBUNIT p25; RPP25","url":"https://www.omim.org/entry/619235"},{"mim_id":"606113","title":"POP7 HOMOLOG, RIBONUCLEASE P/MRP SUBUNIT; POP7","url":"https://www.omim.org/entry/606113"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoli","reliability":"Supported"},{"location":"Vesicles","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/POP7"},"hgnc":{"alias_symbol":["RPP20","RPP2"],"prev_symbol":[]},"alphafold":{"accession":"O75817","domains":[{"cath_id":"3.30.110.20","chopping":"33-135","consensus_level":"high","plddt":90.3298,"start":33,"end":135}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O75817","model_url":"https://alphafold.ebi.ac.uk/files/AF-O75817-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O75817-F1-predicted_aligned_error_v6.png","plddt_mean":83.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=POP7","jax_strain_url":"https://www.jax.org/strain/search?query=POP7"},"sequence":{"accession":"O75817","fasta_url":"https://rest.uniprot.org/uniprotkb/O75817.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O75817/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O75817"}},"corpus_meta":[{"pmid":"20977308","id":"PMC_20977308","title":"Functional analysis of the Asian soybean rust resistance pathway mediated by Rpp2.","date":"2011","source":"Molecular plant-microbe interactions : MPMI","url":"https://pubmed.ncbi.nlm.nih.gov/20977308","citation_count":47,"is_preprint":false},{"pmid":"17717080","id":"PMC_17717080","title":"Specific binding of a Pop6/Pop7 heterodimer to the P3 stem of the yeast RNase MRP and RNase P RNAs.","date":"2007","source":"RNA (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/17717080","citation_count":41,"is_preprint":false},{"pmid":"17119099","id":"PMC_17119099","title":"Heterodimerization regulates RNase MRP/RNase P association, localization, and expression of Rpp20 and Rpp25.","date":"2006","source":"RNA (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/17119099","citation_count":38,"is_preprint":false},{"pmid":"9618478","id":"PMC_9618478","title":"Rpp2, an essential protein subunit of nuclear RNase P, is required for processing of precursor tRNAs and 35S precursor rRNA in Saccharomyces cerevisiae.","date":"1998","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/9618478","citation_count":37,"is_preprint":false},{"pmid":"20215441","id":"PMC_20215441","title":"Heterodimerization of the human RNase P/MRP subunits Rpp20 and Rpp25 is a prerequisite for interaction with the P3 arm of RNase MRP RNA.","date":"2010","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/20215441","citation_count":33,"is_preprint":false},{"pmid":"14715275","id":"PMC_14715275","title":"Rpp20 interacts with SMN and is re-distributed into SMN granules in response to stress.","date":"2004","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/14715275","citation_count":29,"is_preprint":false},{"pmid":"25504467","id":"PMC_25504467","title":"Fine mapping of the Asian soybean rust resistance gene Rpp2 from soybean PI 230970.","date":"2014","source":"TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik","url":"https://pubmed.ncbi.nlm.nih.gov/25504467","citation_count":20,"is_preprint":false},{"pmid":"33571640","id":"PMC_33571640","title":"Crystal structure of human RPP20-RPP25 proteins in complex with the P3 domain of lncRNA RMRP.","date":"2021","source":"Journal of structural biology","url":"https://pubmed.ncbi.nlm.nih.gov/33571640","citation_count":10,"is_preprint":false},{"pmid":"35579257","id":"PMC_35579257","title":"RNA binding protein POP7 regulates ILF3 mRNA stability and expression to promote breast cancer progression.","date":"2022","source":"Cancer science","url":"https://pubmed.ncbi.nlm.nih.gov/35579257","citation_count":10,"is_preprint":false},{"pmid":"29625199","id":"PMC_29625199","title":"Crystal Structure of Human Rpp20/Rpp25 Reveals Quaternary Level Adaptation of the Alba Scaffold as Structural Basis for Single-stranded RNA Binding.","date":"2018","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/29625199","citation_count":9,"is_preprint":false},{"pmid":"20057077","id":"PMC_20057077","title":"Crystallization and preliminary X-ray diffraction analysis of the P3 RNA domain of yeast ribonuclease MRP in a complex with RNase P/MRP protein components Pop6 and Pop7.","date":"2009","source":"Acta crystallographica. Section F, Structural biology and crystallization communications","url":"https://pubmed.ncbi.nlm.nih.gov/20057077","citation_count":6,"is_preprint":false},{"pmid":"41925523","id":"PMC_41925523","title":"Rpp2 Encodes a TIR-NBS-WH-LRR Protein That Confers Resistance to Phakopsora pachyrhizi in Soybean.","date":"2026","source":"Molecular plant-microbe interactions : MPMI","url":"https://pubmed.ncbi.nlm.nih.gov/41925523","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.05.20.652543","title":"Transcriptome Profiling of Resistance Genes Analogs in Soybean’s Cross-Tolerance to Water Limitation and Rust Stress","date":"2025-05-23","source":"bioRxiv","url":"https://doi.org/10.1101/2025.05.20.652543","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7253,"output_tokens":2303,"usd":0.028152},"stage2":{"model":"claude-opus-4-6","input_tokens":5590,"output_tokens":2206,"usd":0.12465},"total_usd":0.152802,"stage1_batch_id":"msgbatch_01SUR8NDzVrNmyszWyJeCct7","stage2_batch_id":"msgbatch_01G7Yfutko3cDWzejrwH5AMx","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2007,\n      \"finding\": \"Pop6 and Pop7 (yeast orthologs of human Rpp25 and Rpp20) form a soluble heterodimer that binds the P3 domain of both RNase MRP and RNase P RNAs. Footprint analysis showed the Pop6/7 complex binds a conserved region of the P3 domain and induces local structural rearrangement of the P3 loop, suggesting it mediates binding of other protein components.\",\n      \"method\": \"Bacterial expression of recombinant proteins, gel mobility shift assays, RNA footprint analysis\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstituted heterodimer, footprinting, gel shift; multiple orthogonal methods in single study\",\n      \"pmids\": [\"17717080\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Rpp2 (yeast ortholog of human POP7/Rpp20) is a protein subunit of nuclear RNase P and RNase MRP; depletion of Rpp2 in vivo causes accumulation of precursor tRNAs with unprocessed introns and 5'/3' termini, and defects in processing of 35S precursor rRNA and 5.8S rRNA. Rpp2 immunoprecipitates cleave precursor tRNAs and rRNAs at expected sites and co-associate with the Rpp1 protein (ortholog of human Rpp30).\",\n      \"method\": \"Epitope-tagged immunoprecipitation, in vivo depletion, in vitro cleavage assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP, in vivo depletion with defined phenotypic readout, in vitro cleavage assay\",\n      \"pmids\": [\"9618478\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Human Rpp20 (POP7 ortholog) and Rpp25 form a salt- and detergent-resistant heterodimer; heterodimerization strongly enhances their interaction with the P3 domain of RNase MRP RNA. Only a single copy of each protein associates with RNase MRP/P particles. Nucleolar accumulation of Rpp20 is strongly dependent on its interaction with Rpp25. Knockdown and overexpression experiments show their expression levels are codependent.\",\n      \"method\": \"Co-immunoprecipitation, gel filtration, RNA binding assays, immunofluorescence, knockdown/overexpression\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (co-IP, localization, KD/OE, RNA binding), replicated in human cells\",\n      \"pmids\": [\"17119099\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Human Rpp20 and Rpp25 individually bind the P3 arm of RNase MRP RNA with negligible affinity, but the 1:1 Rpp20:Rpp25 heterodimer binds the same target with nM affinity, establishing that heterodimer formation is a prerequisite for RNA recognition. Deletion analysis mapped the Alba-type core domain of both proteins as containing the key determinants for mutual association and P3 RNA binding.\",\n      \"method\": \"In vitro binding assays, biophysical characterization (CD, ITC/SPR implied), deletion mutagenesis\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — quantitative in vitro reconstitution with mutagenesis, unambiguous demonstration of cooperativity\",\n      \"pmids\": [\"20215441\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Human Rpp20 (POP7) interacts with SMN protein; the interaction was identified by yeast two-hybrid and validated by in vitro binding assays and co-immunoprecipitation. Exons 3-4 of SMN are necessary and sufficient for Rpp20 binding. In response to stress, SMN aggregates and redistributes Rpp20 from a diffuse nuclear/cytoplasmic distribution into punctuated cytoplasmic SMN granules.\",\n      \"method\": \"Yeast two-hybrid, in vitro binding assay, co-immunoprecipitation, immunofluorescence\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — multiple methods (Y2H, in vitro binding, co-IP, IF) but single lab and interaction domain mapped only on SMN side\",\n      \"pmids\": [\"14715275\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Crystal structure of the human Rpp20/Rpp25 (POP7/Rpp25) heterodimer was determined, revealing quaternary-level differences from archaeal Alba homodimers as the structural basis for adaptation to single-stranded RNA binding specificity in the P3 internal loop of RNase P/MRP.\",\n      \"method\": \"X-ray crystallography, comparative structural analysis\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with comparative functional interpretation\",\n      \"pmids\": [\"29625199\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Crystal structure of human RPP20-RPP25 (POP7-Rpp25) in complex with the P3 domain of lncRNA RMRP was determined; RPP20-RPP25 binds P3 RNA via a conserved positively-charged surface interacting with the distal stem and internal loop regions of P3. Disease-related RMRP mutations cluster at the protein-RNA interface. The structure also reveals a homodimeric organization of the entire RPP20-RPP25-RMRP P3 complex, suggesting dimerization of human RNase MRP complex in cells.\",\n      \"method\": \"X-ray crystallography\",\n      \"journal\": \"Journal of structural biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure of ternary complex with disease-mutation mapping at interface\",\n      \"pmids\": [\"33571640\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Crystals of a complex containing the P3 RNA domain of yeast RNase MRP with Pop6 and Pop7 proteins were obtained and diffracted to 3.25 Å, enabling structural analysis of how these proteins interact with the P3 RNA.\",\n      \"method\": \"X-ray crystallography (crystallization and preliminary diffraction)\",\n      \"journal\": \"Acta crystallographica. Section F, Structural biology and crystallization communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 method but only preliminary crystallographic data reported, no refined structure\",\n      \"pmids\": [\"20057077\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Human POP7 binds preferentially to intron regions of mRNAs (identified by RIP-seq) and promotes breast cancer progression by stabilizing ILF3 mRNA; knockdown of ILF3 impaired the malignant phenotypes conferred by POP7 overexpression, placing POP7 upstream of ILF3 in this pathway.\",\n      \"method\": \"RNA immunoprecipitation sequencing (RIP-seq), mRNA stability assay, knockdown/overexpression with functional readouts (proliferation, invasion, in vivo tumor growth)\",\n      \"journal\": \"Cancer science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — RIP-seq plus epistasis by knockdown, single lab study\",\n      \"pmids\": [\"35579257\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"POP7 (human Rpp20/yeast Rpp2) is a subunit of both RNase P and RNase MRP that obligatorily heterodimerizes with Rpp25 (Pop6 in yeast) to form a complex that binds the P3 RNA domain of these ribonucleases with nM affinity, a interaction structurally mediated by a conserved positively-charged surface of the heterodimer and required for catalytic activity (tRNA 5' leader removal and rRNA processing); the heterodimer also regulates nucleolar localization and protein stability of both subunits, and has been found to interact with SMN and to regulate ILF3 mRNA stability in cancer cells.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"POP7 (also known as Rpp20; yeast ortholog Rpp2/Pop7) is an obligate subunit of both RNase P and RNase MRP ribonucleoprotein complexes, where it functions in tRNA 5'-leader processing and pre-rRNA maturation. POP7 forms a salt-resistant heterodimer with Rpp25 (Pop6 in yeast) through their conserved Alba-type core domains; neither subunit alone binds the P3 RNA domain of RNase MRP/P with appreciable affinity, but the 1:1 heterodimer engages the P3 internal loop and distal stem via a conserved positively charged surface with nanomolar affinity, and this interaction is required for catalytic activity and nucleolar localization [PMID:17717080, PMID:20215441, PMID:33571640]. Crystal structures of the free heterodimer and its ternary complex with the RMRP P3 domain reveal quaternary-level divergence from archaeal Alba homodimers that underlies single-stranded RNA recognition specificity, and show that disease-causing RMRP mutations cluster at the protein–RNA interface [PMID:29625199, PMID:33571640]. Beyond its canonical ribonuclease roles, POP7 binds intronic regions of mRNAs and stabilizes ILF3 mRNA to promote breast cancer cell proliferation and invasion [PMID:35579257].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Establishing POP7 (Rpp2) as an essential subunit of both RNase P and RNase MRP resolved that the same protein participates in tRNA 5'-end processing and pre-rRNA maturation.\",\n      \"evidence\": \"Epitope-tagged immunoprecipitation, in vivo depletion, and in vitro cleavage assays in yeast\",\n      \"pmids\": [\"9618478\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Mechanism by which Rpp2 contributes to catalysis was unknown\",\n        \"Direct RNA-binding site not identified\",\n        \"Physical partners within the holoenzyme not mapped\"\n      ]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Identification of SMN as a physical interaction partner of POP7 raised the possibility that RNase P/MRP components participate in stress-granule biology or SMN-dependent pathways.\",\n      \"evidence\": \"Yeast two-hybrid, in vitro binding, co-immunoprecipitation, and immunofluorescence in human cells\",\n      \"pmids\": [\"14715275\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Interaction mapped only on the SMN side (exons 3–4); POP7 binding determinants undefined\",\n        \"Functional consequence of POP7–SMN interaction not established\",\n        \"Not independently replicated\"\n      ]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Demonstrating that Rpp20 and Rpp25 form a stable obligate heterodimer whose assembly is prerequisite for P3 RNA binding and nucleolar localization explained how two individually weak RNA-binding proteins achieve high-affinity recognition and co-regulate each other's stability.\",\n      \"evidence\": \"Co-immunoprecipitation, gel filtration, RNA binding assays, immunofluorescence, knockdown/overexpression in human cells\",\n      \"pmids\": [\"17119099\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis of heterodimerization unknown\",\n        \"Whether dimerization is sufficient for holoenzyme assembly not tested\"\n      ]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Footprinting of the yeast Pop6–Pop7 complex on P3 RNA revealed that the heterodimer induces local structural rearrangement of the P3 loop, suggesting it primes the RNA for recruitment of additional protein subunits.\",\n      \"evidence\": \"Recombinant protein expression, gel mobility shift, RNA footprinting in vitro\",\n      \"pmids\": [\"17717080\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Identity of subsequently recruited subunits not determined\",\n        \"No atomic-resolution view of the RNA conformational change\"\n      ]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Quantitative binding measurements and deletion mutagenesis pinpointed the Alba-type core domains as the minimal determinants for both heterodimerization and cooperative nM-affinity P3 RNA binding, definitively establishing cooperativity as the mechanism underlying RNA recognition.\",\n      \"evidence\": \"In vitro binding assays with deletion mutants, biophysical characterization\",\n      \"pmids\": [\"20215441\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No structure of the RNA-bound complex\",\n        \"Contributions of regions outside the Alba core not fully resolved\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"The crystal structure of the free Rpp20–Rpp25 heterodimer revealed how quaternary-level divergence from archaeal Alba homodimers adapted the complex for single-stranded RNA recognition in the P3 internal loop.\",\n      \"evidence\": \"X-ray crystallography with comparative structural analysis\",\n      \"pmids\": [\"29625199\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structure lacked bound RNA, so the RNA-recognition interface was inferred rather than observed\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"The co-crystal structure of RPP20–RPP25 with the RMRP P3 domain provided the first atomic view of the protein–RNA interface, showing that a conserved positively charged surface contacts the distal stem and internal loop, and that cartilage-hair hypoplasia RMRP mutations cluster at this interface.\",\n      \"evidence\": \"X-ray crystallography of the ternary complex\",\n      \"pmids\": [\"33571640\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Homodimeric organization of the ternary complex awaits validation in the context of the full holoenzyme\",\n        \"Functional impact of individual interface mutations not tested by mutagenesis-activity assays\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Discovery that POP7 binds mRNA introns and stabilizes ILF3 mRNA to promote breast cancer progression expanded its functional repertoire beyond canonical RNase P/MRP activities.\",\n      \"evidence\": \"RIP-seq, mRNA stability assays, knockdown/overexpression with proliferation and invasion readouts in breast cancer cells and xenografts\",\n      \"pmids\": [\"35579257\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism of mRNA stabilization not defined (direct vs. indirect)\",\n        \"Single-lab finding; not independently replicated\",\n        \"Relationship between RNase MRP function and mRNA stabilization role unclear\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How POP7–Rpp25 heterodimer assembly integrates into full RNase P and RNase MRP holoenzyme architecture and catalytic mechanism in human cells remains unresolved, as does the physiological significance of the SMN interaction and the non-canonical mRNA-stabilizing activity.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No cryo-EM or crystal structure of the complete human RNase P or MRP holoenzyme with POP7 positioned\",\n        \"SMN interaction has no established functional consequence\",\n        \"mRNA stabilization mechanism and its relationship to canonical ribonuclease function are undefined\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [0, 2, 3, 6, 8]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 2, 5, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [2, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [1, 0, 3, 6]}\n    ],\n    \"complexes\": [\n      \"RNase P\",\n      \"RNase MRP\"\n    ],\n    \"partners\": [\n      \"RPP25\",\n      \"RPP30\",\n      \"SMN1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}