{"gene":"POP7","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":2007,"finding":"Bacterially expressed yeast Pop6 and Pop7 form a soluble heterodimer that binds the RNA components of both RNase MRP and RNase P. Footprint analysis demonstrated that the Pop6/Pop7 complex binds specifically to a conserved region of the P3 domain of RNase MRP RNA, and binding leads to local rearrangement in the structure of the P3 loop, suggesting the complex mediates binding of other protein components.","method":"Bacterial co-expression/reconstitution of heterodimer, RNA footprint analysis, gel mobility shift assay","journal":"RNA (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution of heterodimer, footprint analysis, and gel mobility assays; foundational mechanistic study","pmids":["17717080"],"is_preprint":false},{"year":2006,"finding":"Human Rpp20 (POP7) and Rpp25 form a salt- and detergent-resistant heterodimer; heterodimerization strongly enhances their interaction with the P3 domain of RNase MRP RNA. Coimmunoprecipitation showed only a single copy of each protein associates with RNase MRP and RNase P particles. Nucleolar accumulation of Rpp20 is strongly dependent on its interaction with Rpp25. Overexpression and knockdown experiments showed that expression levels of Rpp20 and Rpp25 are codependent.","method":"Co-immunoprecipitation, RNA-binding assays, knockdown/overexpression, immunofluorescence localization","journal":"RNA (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (Co-IP, RNA-binding, localization, knockdown/OE), replicated across human system","pmids":["17119099"],"is_preprint":false},{"year":2010,"finding":"In vitro analysis demonstrated that individual Rpp20 (POP7) or Rpp25 subunits have negligible affinity for the P3 arm of RNase MRP RNA, whereas the 1:1 Rpp20:Rpp25 heterodimer binds the P3 RNA with nM affinity. The heterodimer is formed prior to RNA binding. The Alba-type core domain of both proteins contains most of the determinants for mutual association and P3 RNA recognition; N- and C-terminal deletions mapped these determinants using deletion mutant proteins.","method":"In vitro binding assays (biophysical/biochemical), circular dichroism, deletion mutagenesis, quantitative affinity measurements","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Strong — quantitative in vitro reconstitution with mutagenesis, unambiguous demonstration of heterodimerization prerequisite for RNA binding","pmids":["20215441"],"is_preprint":false},{"year":2004,"finding":"Human Rpp20 (POP7) physically interacts with the SMN protein (mutated in spinal muscular atrophy); SMN exons 3–4 are necessary and sufficient for binding to Rpp20. SMA-associated mutations in SMN's YG domain abrogate or reduce binding. In response to cellular stress, SMN redistributes Rpp20 from its diffuse nucleo-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 / Moderate — reciprocal Co-IP and in vitro binding, single lab, multiple orthogonal methods","pmids":["14715275"],"is_preprint":false},{"year":2018,"finding":"Crystal structure of the human Rpp20/Rpp25 (POP7/RPP25) heterodimer revealed that the evolutionary divergence from archaeal Alba chromatin protein dimers toward single-stranded RNA binding specificity arises primarily from quaternary-level differences at the heterodimerization interface, providing structural basis for P3 RNA binding by the heterodimer.","method":"X-ray crystallography, comparative structural analysis","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure with comparative structural analysis, single lab but high-resolution structural method","pmids":["29625199"],"is_preprint":false},{"year":2021,"finding":"Crystal structure of human RPP20-RPP25 (POP7-RPP25) in complex with the P3 domain of RMRP lncRNA showed that P3 RNA binds a conserved positively-charged surface of the RPP20-RPP25 heterodimer through its distal stem and internal loop regions. Disease-related RMRP P3 mutations are located at the protein-RNA interface and likely weaken this binding. The structure also revealed a homodimeric organization of the entire RPP20-RPP25-RMRPP3 complex, suggesting possible dimerization of human RNase MRP in cells, and a tetrameric feature conserved with archaeal Alba proteins.","method":"X-ray crystallography, structural analysis of disease mutations at interface","journal":"Journal of structural biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure of ternary complex with structural mapping of disease mutations, single lab","pmids":["33571640"],"is_preprint":false},{"year":2022,"finding":"POP7 (RPP20) binds preferentially to intron regions of mRNA targets as determined by RIP-seq in breast cancer cells. POP7 regulates ILF3 mRNA stability and expression; knockdown of ILF3 impaired the increased malignant phenotype of POP7-overexpressing cells, placing POP7 upstream of ILF3 in a cancer-relevant pathway.","method":"RNA immunoprecipitation coupled with sequencing (RIP-seq), mRNA stability assay, knockdown/overexpression with phenotypic readout","journal":"Cancer science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RIP-seq for binding, mRNA stability assay, epistasis by knockdown rescue, single lab","pmids":["35579257"],"is_preprint":false},{"year":2009,"finding":"Crystals of the yeast P3 RNA domain in complex with Pop6 and Pop7 (selenomethionine derivatives) were obtained, confirming the formation of a stable ternary complex amenable to structural study; diffraction to 3.25 Å established structural tractability of the Pop6/Pop7-P3 RNA complex.","method":"X-ray crystallography (crystal structure determination at 3.25 Å)","journal":"Acta crystallographica. Section F, Structural biology and crystallization communications","confidence":"Low","confidence_rationale":"Tier 1 / Weak — preliminary crystallization/diffraction report only, no functional validation reported in this abstract","pmids":["20057077"],"is_preprint":false}],"current_model":"POP7 (RPP20) obligatorily heterodimerizes with RPP25 (Rpp25/Pop6 in yeast) through their conserved Alba-type core domains; this heterodimer, but not either subunit alone, binds with nM affinity to the P3 stem-loop domain of both RNase P and RNase MRP RNAs via a conserved positively-charged surface (structurally defined by crystal structures), where the interaction induces local RNA rearrangements and scaffolds assembly of additional protein subunits; nucleolar localization of POP7 depends on its association with RPP25; POP7 also interacts with SMN and is redistributed to cytoplasmic stress granules under stress; and independently of its RNase P/MRP role, POP7 binds mRNA intron regions and stabilizes ILF3 mRNA to promote breast cancer cell proliferation and metastasis."},"narrative":{"mechanistic_narrative":"POP7 (RPP20) is a shared protein subunit of the ribonucleoprotein endoribonucleases RNase P and RNase MRP that functions strictly as an obligate heterodimer with RPP25 [PMID:17119099, PMID:20215441]. Neither subunit alone has appreciable affinity for the RNA component; the preformed 1:1 RPP20:RPP25 heterodimer binds the conserved P3 stem-loop domain of both RNase P and RNase MRP RNAs with nanomolar affinity, with the determinants for both mutual association and P3 RNA recognition residing in the Alba-type core domain of each protein [PMID:17717080, PMID:20215441]. Crystal structures of the heterodimer and of its ternary complex with the RMRP P3 RNA show that the RNA contacts a conserved positively-charged surface through its distal stem and internal loop, and that the heterodimer's single-stranded RNA-binding specificity arose from quaternary-level divergence from archaeal Alba chromatin dimers; disease-related RMRP P3 mutations map to the protein-RNA interface [PMID:29625199, PMID:33571640]. Binding induces local rearrangement of the P3 loop, positioning the heterodimer to scaffold assembly of additional protein subunits, and only a single copy of each protein associates per particle [PMID:17717080, PMID:17119099]. Nucleolar accumulation of POP7, and its protein stability, are codependent on RPP25 [PMID:17119099]. POP7 additionally interacts with the SMN protein and is redistributed into cytoplasmic stress granules upon cellular stress [PMID:14715275]. Independently of its RNase P/MRP role, POP7 binds intron regions of mRNA targets and stabilizes ILF3 mRNA to drive a malignant phenotype in breast cancer cells [PMID:35579257].","teleology":[{"year":2004,"claim":"Established the first POP7 protein partner outside the RNase P/MRP enzymes, linking POP7 to the SMN complex and to a stress-responsive subcellular relocalization.","evidence":"Yeast two-hybrid, in vitro binding, Co-IP and immunofluorescence in human cells","pmids":["14715275"],"confidence":"Medium","gaps":["Functional consequence of the SMN-POP7 interaction for RNase P/MRP biogenesis not defined","Single lab; physiological role of stress-granule redistribution unresolved"]},{"year":2006,"claim":"Demonstrated that POP7 acts as an obligate heterodimer with RPP25, that this pairing enhances P3 RNA binding, and that POP7 nucleolar localization and protein stability depend on RPP25.","evidence":"Co-IP, RNA-binding assays, knockdown/overexpression and immunofluorescence in human cells","pmids":["17119099"],"confidence":"High","gaps":["Did not resolve atomic basis of heterodimerization or RNA contact","Stoichiometry within the full enzyme particle inferred by Co-IP only"]},{"year":2007,"claim":"Showed in the yeast orthologs that the Pop6/Pop7 heterodimer binds a conserved P3 region of both RNase MRP and RNase P RNA and remodels the P3 loop, implicating it as a nucleating scaffold for other subunits.","evidence":"Bacterial co-expression/reconstitution, RNA footprinting and gel mobility shift","pmids":["17717080"],"confidence":"High","gaps":["Identity of subsequently recruited subunits not established","Conservation of scaffolding role in human enzyme not directly tested here"]},{"year":2010,"claim":"Quantified that heterodimerization is a strict prerequisite for high-affinity P3 RNA binding and mapped the determinants to the Alba-type core domains.","evidence":"In vitro binding assays, circular dichroism, deletion mutagenesis and quantitative affinity measurement","pmids":["20215441"],"confidence":"High","gaps":["Did not provide a structural model of the interface","Roles of N/C-terminal extensions beyond RNA binding not addressed"]},{"year":2009,"claim":"Achieved a tractable crystal of the yeast Pop6/Pop7-P3 RNA ternary complex, confirming a stable assembly suitable for atomic structure determination.","evidence":"X-ray crystallography, diffraction to 3.25 A (preliminary crystallization report)","pmids":["20057077"],"confidence":"Low","gaps":["Preliminary crystallization/diffraction report only; no functional validation","No refined structure or interface description in this report"]},{"year":2018,"claim":"Provided the structural basis for how the heterodimer acquired single-stranded RNA-binding specificity, tracing it to quaternary differences from archaeal Alba dimers.","evidence":"X-ray crystallography of the human RPP20/RPP25 heterodimer with comparative structural analysis","pmids":["29625199"],"confidence":"High","gaps":["Structure of the heterodimer alone, without bound P3 RNA","Single lab"]},{"year":2021,"claim":"Resolved the human heterodimer bound to RMRP P3 RNA, defining the positively-charged binding surface and rationalizing disease-causing RMRP mutations at the interface, plus a possible higher-order dimerization of RNase MRP.","evidence":"X-ray crystallography of the ternary complex with structural mapping of disease mutations","pmids":["33571640"],"confidence":"High","gaps":["In-cell relevance of the proposed homodimeric/tetrameric organization not validated","Functional impact of mapped RMRP mutations on enzyme activity inferred structurally"]},{"year":2022,"claim":"Uncovered an RNase P/MRP-independent role: POP7 binds mRNA introns and stabilizes ILF3 mRNA to promote breast cancer proliferation and metastasis.","evidence":"RIP-seq, mRNA stability assay, knockdown/overexpression with phenotypic rescue in breast cancer cells","pmids":["35579257"],"confidence":"Medium","gaps":["Whether intron binding requires RPP25 or the heterodimer is unknown","Single lab; mechanism of mRNA stabilization not defined"]},{"year":null,"claim":"How POP7's canonical RNase P/MRP scaffolding role relates mechanistically to its moonlighting mRNA-stabilizing and SMN/stress-granule activities remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No evidence on whether the heterodimer or free POP7 mediates the mRNA-stabilizing function","No integrated model linking nucleolar enzyme assembly to cytoplasmic/stress roles"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[0,1,2,5,6]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,2]}],"localization":[{"term_id":"GO:0005730","term_label":"nucleolus","supporting_discovery_ids":[1]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[3]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[0,1,2]}],"complexes":["RNase P","RNase MRP","RPP20-RPP25 heterodimer"],"partners":["RPP25","SMN1"],"other_free_text":[]}},"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":"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":42,"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":"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":34,"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":"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":11,"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":10,"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}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":5501,"output_tokens":2214,"usd":0.024857,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9278,"output_tokens":2946,"usd":0.06002,"stage2_stop_reason":"end_turn"},"total_usd":0.084877,"stage1_batch_id":"msgbatch_01CNoDbkChHEkgrJnL7BwtGJ","stage2_batch_id":"msgbatch_016Y4x9E9Wg5VQDANj9quSQD","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2007,\n      \"finding\": \"Bacterially expressed yeast Pop6 and Pop7 form a soluble heterodimer that binds the RNA components of both RNase MRP and RNase P. Footprint analysis demonstrated that the Pop6/Pop7 complex binds specifically to a conserved region of the P3 domain of RNase MRP RNA, and binding leads to local rearrangement in the structure of the P3 loop, suggesting the complex mediates binding of other protein components.\",\n      \"method\": \"Bacterial co-expression/reconstitution of heterodimer, RNA footprint analysis, gel mobility shift assay\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution of heterodimer, footprint analysis, and gel mobility assays; foundational mechanistic study\",\n      \"pmids\": [\"17717080\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Human Rpp20 (POP7) and Rpp25 form a salt- and detergent-resistant heterodimer; heterodimerization strongly enhances their interaction with the P3 domain of RNase MRP RNA. Coimmunoprecipitation showed only a single copy of each protein associates with RNase MRP and RNase P particles. Nucleolar accumulation of Rpp20 is strongly dependent on its interaction with Rpp25. Overexpression and knockdown experiments showed that expression levels of Rpp20 and Rpp25 are codependent.\",\n      \"method\": \"Co-immunoprecipitation, RNA-binding assays, knockdown/overexpression, immunofluorescence localization\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (Co-IP, RNA-binding, localization, knockdown/OE), replicated across human system\",\n      \"pmids\": [\"17119099\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"In vitro analysis demonstrated that individual Rpp20 (POP7) or Rpp25 subunits have negligible affinity for the P3 arm of RNase MRP RNA, whereas the 1:1 Rpp20:Rpp25 heterodimer binds the P3 RNA with nM affinity. The heterodimer is formed prior to RNA binding. The Alba-type core domain of both proteins contains most of the determinants for mutual association and P3 RNA recognition; N- and C-terminal deletions mapped these determinants using deletion mutant proteins.\",\n      \"method\": \"In vitro binding assays (biophysical/biochemical), circular dichroism, deletion mutagenesis, quantitative affinity measurements\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — quantitative in vitro reconstitution with mutagenesis, unambiguous demonstration of heterodimerization prerequisite for RNA binding\",\n      \"pmids\": [\"20215441\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Human Rpp20 (POP7) physically interacts with the SMN protein (mutated in spinal muscular atrophy); SMN exons 3–4 are necessary and sufficient for binding to Rpp20. SMA-associated mutations in SMN's YG domain abrogate or reduce binding. In response to cellular stress, SMN redistributes Rpp20 from its diffuse nucleo-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 / Moderate — reciprocal Co-IP and in vitro binding, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"14715275\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Crystal structure of the human Rpp20/Rpp25 (POP7/RPP25) heterodimer revealed that the evolutionary divergence from archaeal Alba chromatin protein dimers toward single-stranded RNA binding specificity arises primarily from quaternary-level differences at the heterodimerization interface, providing structural basis for P3 RNA binding by the heterodimer.\",\n      \"method\": \"X-ray crystallography, comparative structural analysis\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure with comparative structural analysis, single lab but high-resolution structural method\",\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 RMRP lncRNA showed that P3 RNA binds a conserved positively-charged surface of the RPP20-RPP25 heterodimer through its distal stem and internal loop regions. Disease-related RMRP P3 mutations are located at the protein-RNA interface and likely weaken this binding. The structure also revealed a homodimeric organization of the entire RPP20-RPP25-RMRPP3 complex, suggesting possible dimerization of human RNase MRP in cells, and a tetrameric feature conserved with archaeal Alba proteins.\",\n      \"method\": \"X-ray crystallography, structural analysis of disease mutations at interface\",\n      \"journal\": \"Journal of structural biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure of ternary complex with structural mapping of disease mutations, single lab\",\n      \"pmids\": [\"33571640\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"POP7 (RPP20) binds preferentially to intron regions of mRNA targets as determined by RIP-seq in breast cancer cells. POP7 regulates ILF3 mRNA stability and expression; knockdown of ILF3 impaired the increased malignant phenotype of POP7-overexpressing cells, placing POP7 upstream of ILF3 in a cancer-relevant pathway.\",\n      \"method\": \"RNA immunoprecipitation coupled with sequencing (RIP-seq), mRNA stability assay, knockdown/overexpression with phenotypic readout\",\n      \"journal\": \"Cancer science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RIP-seq for binding, mRNA stability assay, epistasis by knockdown rescue, single lab\",\n      \"pmids\": [\"35579257\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Crystals of the yeast P3 RNA domain in complex with Pop6 and Pop7 (selenomethionine derivatives) were obtained, confirming the formation of a stable ternary complex amenable to structural study; diffraction to 3.25 Å established structural tractability of the Pop6/Pop7-P3 RNA complex.\",\n      \"method\": \"X-ray crystallography (crystal structure determination at 3.25 Å)\",\n      \"journal\": \"Acta crystallographica. Section F, Structural biology and crystallization communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 1 / Weak — preliminary crystallization/diffraction report only, no functional validation reported in this abstract\",\n      \"pmids\": [\"20057077\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"POP7 (RPP20) obligatorily heterodimerizes with RPP25 (Rpp25/Pop6 in yeast) through their conserved Alba-type core domains; this heterodimer, but not either subunit alone, binds with nM affinity to the P3 stem-loop domain of both RNase P and RNase MRP RNAs via a conserved positively-charged surface (structurally defined by crystal structures), where the interaction induces local RNA rearrangements and scaffolds assembly of additional protein subunits; nucleolar localization of POP7 depends on its association with RPP25; POP7 also interacts with SMN and is redistributed to cytoplasmic stress granules under stress; and independently of its RNase P/MRP role, POP7 binds mRNA intron regions and stabilizes ILF3 mRNA to promote breast cancer cell proliferation and metastasis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"POP7 (RPP20) is a shared protein subunit of the ribonucleoprotein endoribonucleases RNase P and RNase MRP that functions strictly as an obligate heterodimer with RPP25 [#1, #2]. Neither subunit alone has appreciable affinity for the RNA component; the preformed 1:1 RPP20:RPP25 heterodimer binds the conserved P3 stem-loop domain of both RNase P and RNase MRP RNAs with nanomolar affinity, with the determinants for both mutual association and P3 RNA recognition residing in the Alba-type core domain of each protein [#0, #2]. Crystal structures of the heterodimer and of its ternary complex with the RMRP P3 RNA show that the RNA contacts a conserved positively-charged surface through its distal stem and internal loop, and that the heterodimer's single-stranded RNA-binding specificity arose from quaternary-level divergence from archaeal Alba chromatin dimers; disease-related RMRP P3 mutations map to the protein-RNA interface [#4, #5]. Binding induces local rearrangement of the P3 loop, positioning the heterodimer to scaffold assembly of additional protein subunits, and only a single copy of each protein associates per particle [#0, #1]. Nucleolar accumulation of POP7, and its protein stability, are codependent on RPP25 [#1]. POP7 additionally interacts with the SMN protein and is redistributed into cytoplasmic stress granules upon cellular stress [#3]. Independently of its RNase P/MRP role, POP7 binds intron regions of mRNA targets and stabilizes ILF3 mRNA to drive a malignant phenotype in breast cancer cells [#6].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Established the first POP7 protein partner outside the RNase P/MRP enzymes, linking POP7 to the SMN complex and to a stress-responsive subcellular relocalization.\",\n      \"evidence\": \"Yeast two-hybrid, in vitro binding, Co-IP and immunofluorescence in human cells\",\n      \"pmids\": [\"14715275\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Functional consequence of the SMN-POP7 interaction for RNase P/MRP biogenesis not defined\", \"Single lab; physiological role of stress-granule redistribution unresolved\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Demonstrated that POP7 acts as an obligate heterodimer with RPP25, that this pairing enhances P3 RNA binding, and that POP7 nucleolar localization and protein stability depend on RPP25.\",\n      \"evidence\": \"Co-IP, RNA-binding assays, knockdown/overexpression and immunofluorescence in human cells\",\n      \"pmids\": [\"17119099\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Did not resolve atomic basis of heterodimerization or RNA contact\", \"Stoichiometry within the full enzyme particle inferred by Co-IP only\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Showed in the yeast orthologs that the Pop6/Pop7 heterodimer binds a conserved P3 region of both RNase MRP and RNase P RNA and remodels the P3 loop, implicating it as a nucleating scaffold for other subunits.\",\n      \"evidence\": \"Bacterial co-expression/reconstitution, RNA footprinting and gel mobility shift\",\n      \"pmids\": [\"17717080\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Identity of subsequently recruited subunits not established\", \"Conservation of scaffolding role in human enzyme not directly tested here\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Quantified that heterodimerization is a strict prerequisite for high-affinity P3 RNA binding and mapped the determinants to the Alba-type core domains.\",\n      \"evidence\": \"In vitro binding assays, circular dichroism, deletion mutagenesis and quantitative affinity measurement\",\n      \"pmids\": [\"20215441\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Did not provide a structural model of the interface\", \"Roles of N/C-terminal extensions beyond RNA binding not addressed\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Achieved a tractable crystal of the yeast Pop6/Pop7-P3 RNA ternary complex, confirming a stable assembly suitable for atomic structure determination.\",\n      \"evidence\": \"X-ray crystallography, diffraction to 3.25 A (preliminary crystallization report)\",\n      \"pmids\": [\"20057077\"],\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Preliminary crystallization/diffraction report only; no functional validation\", \"No refined structure or interface description in this report\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Provided the structural basis for how the heterodimer acquired single-stranded RNA-binding specificity, tracing it to quaternary differences from archaeal Alba dimers.\",\n      \"evidence\": \"X-ray crystallography of the human RPP20/RPP25 heterodimer with comparative structural analysis\",\n      \"pmids\": [\"29625199\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Structure of the heterodimer alone, without bound P3 RNA\", \"Single lab\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Resolved the human heterodimer bound to RMRP P3 RNA, defining the positively-charged binding surface and rationalizing disease-causing RMRP mutations at the interface, plus a possible higher-order dimerization of RNase MRP.\",\n      \"evidence\": \"X-ray crystallography of the ternary complex with structural mapping of disease mutations\",\n      \"pmids\": [\"33571640\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"In-cell relevance of the proposed homodimeric/tetrameric organization not validated\", \"Functional impact of mapped RMRP mutations on enzyme activity inferred structurally\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Uncovered an RNase P/MRP-independent role: POP7 binds mRNA introns and stabilizes ILF3 mRNA to promote breast cancer proliferation and metastasis.\",\n      \"evidence\": \"RIP-seq, mRNA stability assay, knockdown/overexpression with phenotypic rescue in breast cancer cells\",\n      \"pmids\": [\"35579257\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Whether intron binding requires RPP25 or the heterodimer is unknown\", \"Single lab; mechanism of mRNA stabilization not defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How POP7's canonical RNase P/MRP scaffolding role relates mechanistically to its moonlighting mRNA-stabilizing and SMN/stress-granule activities remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"No evidence on whether the heterodimer or free POP7 mediates the mRNA-stabilizing function\", \"No integrated model linking nucleolar enzyme assembly to cytoplasmic/stress roles\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [0, 1, 2, 5, 6]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [0, 1, 2]}\n    ],\n    \"complexes\": [\"RNase P\", \"RNase MRP\", \"RPP20-RPP25 heterodimer\"],\n    \"partners\": [\"RPP25\", \"SMN1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}