{"gene":"LSM2","run_date":"2026-04-28T18:30:27","timeline":{"discoveries":[{"year":1999,"finding":"Human LSm proteins (including LSm2) form a stable doughnut-shaped heteromeric complex that binds specifically to the 3'-terminal U-tract of U6 snRNA and facilitates U4/U6 RNA duplex formation in vitro; the complex does not bind the U-rich Sm sites of intact U1, U2, U4, or U5 snRNAs.","method":"Protein purification, electron microscopy, in vitro RNA binding assay, immunoprecipitation","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — reconstituted complex, EM structure, in vitro functional assay with specificity controls","pmids":["10523320"],"is_preprint":false},{"year":2001,"finding":"In yeast, LSM2 and LSM4 (but not other LSM genes) act as allele-specific low-copy suppressors of mutations in Lsm8p; overexpression of LSM2 increases levels of both Lsm8p and U6 snRNPs, consistent with Lsm2p and Lsm4p directly contacting Lsm8p within the Lsm2-8 ring; the entire Lsm2-8 complex acts redundantly with La protein (Lhp1p) to stabilize nascent U6 snRNA.","method":"Genetic suppressor analysis, overexpression experiments, snRNP level quantification","journal":"Genetics","confidence":"High","confidence_rationale":"Tier 2 — allele-specific suppression and biochemical quantification, consistent model across multiple genetic tests","pmids":["11333229"],"is_preprint":false},{"year":2002,"finding":"Human LSm1-7 proteins (not LSm8) colocalize with mRNA-degrading enzymes Dcp1/2 and Xrn1 in discrete cytoplasmic foci (P-bodies); LSm8 is excluded from these foci, delineating distinct cytoplasmic (LSm1-7) and nuclear (LSm2-8) complexes; complex formation is required for enrichment in cytoplasmic foci.","method":"Subcellular localization by immunofluorescence, FRET, co-expression of wild-type and dominant-negative LSm mutants","journal":"RNA (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 2 — direct localization with FRET validation and functional mutagenesis, clearly distinguishing LSm2-8 nuclear complex from LSm1-7","pmids":["12515382"],"is_preprint":false},{"year":2004,"finding":"The nuclear Lsm2-8p complex is required for decapping and 5' degradation of nucleus-restricted mRNAs and pre-mRNA degradation intermediates; Lsm8p (but not cytoplasmic Lsm1p) UV-crosslinks directly to nuclear poly(A)+ RNA, indicating the Lsm2-8p complex physically interacts with nuclear RNA substrates and targets them for decapping.","method":"UV crosslinking, genetic deletion analysis, RNA stability assays in yeast strains with nuclear mRNA export blocks","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — direct UV crosslinking combined with genetic epistasis and RNA stability measurements","pmids":["15485930"],"is_preprint":false},{"year":2004,"finding":"A third Lsm complex consisting of Lsm2-Lsm7 (without Lsm1 or Lsm8) associates with the box H/ACA snoRNA snR5 in yeast; in vitro reconstitution shows the 3' end of snR5 is critical for Lsm protein recognition; this Lsm2-7 complex is partially distinct from the canonical snR5 box H/ACA protein complex and localizes to nucleoli, suggesting a nucleolar function for Lsm proteins in snoRNA biogenesis.","method":"In vitro reconstitution of RNA-protein binding, glycerol gradient sedimentation, sequential immunoprecipitation, subcellular fractionation/localization","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro reconstitution plus multiple orthogonal biochemical approaches","pmids":["15075370"],"is_preprint":false},{"year":2007,"finding":"The complete Lsm2-8 complex is required for nuclear accumulation of U6 snRNA in yeast; loss of any single Lsm2-8 subunit causes U6 mislocalization; La protein has a smaller, indirect effect on U6 localization consistent with a chaperone role in Lsm2-8 assembly rather than direct nuclear retention.","method":"In situ hybridization of U6 snRNA in lsm deletion strains, genetic analysis","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 — direct RNA localization measurements across multiple deletion mutants with clear phenotypic readout","pmids":["17251193"],"is_preprint":false},{"year":2007,"finding":"Nuclear accumulation of Lsm proteins in yeast depends on complex formation; Lsm8p plays a crucial role in nuclear localization, with its own localization most strongly influenced by Lsm2p and Lsm4p (its presumed neighbors); Lsm1p and Lsm8p act competitively to partition the shared Lsm2-7 subunits between cytoplasmic and nuclear complexes, and stress shifts Lsm proteins from nucleus to cytoplasm.","method":"Overexpression and depletion experiments, subcellular localization by fluorescence microscopy in yeast","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — systematic overexpression/depletion with direct imaging, showing competitive mechanism","pmids":["18029398"],"is_preprint":false},{"year":2011,"finding":"Crystal structure of the LSm5-6-7 (LSm657) assembly intermediate resolved at 2.5 Å reveals canonical Sm fold monomers arranged in a hexameric ring; NMR and pull-down experiments show that the LSm657 complex can incorporate LSm2-3 to assemble towards native LSm1-7 and LSm2-8 rings, identifying LSm657 as a functional building block on the assembly pathway.","method":"X-ray crystallography (2.5 Å), NMR spectroscopy, pull-down assays","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 — crystal structure plus NMR and pull-down validation of assembly intermediate","pmids":["22001694"],"is_preprint":false},{"year":2013,"finding":"Lsm2 and Lsm3 bridge the interaction between the C-terminus of Pat1 (Pat1C) and the Lsm1-7 complex; crystal structure of the Lsm2-3-Pat1C complex shows three Pat1C molecules surrounding a heptameric Lsm2-3 ring in an asymmetric arrangement; the Lsm2-3-Pat1C complex stimulates mRNA decapping in vitro to a similar extent as full Lsm1-7-Pat1C; structure-based mutagenesis confirmed that Lsm2-3–Pat1C interactions are required for decapping activation in vivo.","method":"Crystal structure determination, in vitro decapping assay, RNA-binding assay, structure-based mutagenesis, yeast in vivo decapping assays","journal":"Cell research","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with reconstituted in vitro functional assay and in vivo mutagenesis validation","pmids":["24247251"],"is_preprint":false},{"year":2017,"finding":"In human cells, Pat1b forms a nuclear complex with the Lsm2-8 heptamer that binds U6 snRNA and interacts with SART3 and additional U4/U6.U5 tri-snRNP components in Cajal bodies; Pat1b depletion causes alternative splicing changes (exon skipping at weak donor sites) as well as upregulation of P-body-enriched mRNAs, demonstrating dual roles for Pat1b/Lsm2-8 in nuclear splicing and cytoplasmic mRNA decay via distinct complexes.","method":"Co-immunoprecipitation, immunofluorescence, RNAi knockdown, RNA sequencing","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP combined with RNA-seq and RNAi, multiple orthogonal methods","pmids":["28768202"],"is_preprint":false},{"year":2018,"finding":"Structure-guided mutagenesis of the yeast Lsm2-8 ring identifies Lsm3-R69A (lethal) and Lsm2-R63A (severe growth defect) as critical RNA-binding residues that contact the 3'-terminal UUU of U6 snRNA; lethal deletions of lsm2, lsm3, lsm4, lsm5, and lsm8 are all rescued by U6 snRNA overexpression, establishing that the sole essential function of the Lsm2-8 ring in yeast is to support U6 snRNA biogenesis/function.","method":"Alanine scanning mutagenesis, high-copy suppressor analysis, genetic rescue with U6 overexpression","journal":"RNA (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1-2 — structure-guided mutagenesis combined with rigorous genetic epistasis across 235 pairwise combinations","pmids":["29615482"],"is_preprint":false},{"year":2020,"finding":"High-resolution cryo-EM structures of Lsm2-8 bound to RNA show that the unique 2',3'-cyclic phosphate end of U6 snRNA is a prime determinant of Lsm2-8 specificity; Lsm5 uniquely recognizes purine bases, explaining its divergent sequence; in contrast, Lsm1-7 strongly discriminates against cyclic phosphates and prefers oligouridylate tracts with terminal purines, revealing the molecular basis for the distinct RNA selectivities of the two complexes.","method":"Cryo-EM structure determination (four high-resolution structures), RNA-binding specificity assays","journal":"RNA (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1 — multiple high-resolution cryo-EM structures with functional RNA-binding specificity characterization","pmids":["32518066"],"is_preprint":false},{"year":2020,"finding":"In C. elegans somatic cells, the LSM2-8 complex contributes to silencing of H3K27me3-marked heterochromatic genes by targeting their transcripts for degradation via the XRN-2 exoribonuclease; disruption of LSM2-8 stabilizes these mRNAs and coincides with a localized reduction of H3K27me3 at sensitive loci; this pathway does not require H3K9 methylation, distinguishing it from other heterochromatic RNA degradation pathways.","method":"Genetic knockdown/knockout, RNA stability assays, chromatin immunoprecipitation for H3K27me3, epistasis with xrn-2","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with XRN-2, RNA stability measurements, and ChIP, replicated across reporters and endogenous genes","pmids":["32251399"],"is_preprint":false},{"year":2020,"finding":"In Arabidopsis, prefoldins (PFDs) interact with LSM2-8 complex components and are required to maintain adequate levels of the complex; LSM8 protein is a client of Hsp90, and PFD4 mediates the interaction between LSM8 and Hsp90; loss of PFDs reduces LSM8 levels and U6 snRNA levels and alters pre-mRNA splicing, establishing a PFD-Hsp90-LSM2-8 axis for spliceosomal complex proteostasis.","method":"Co-expression analysis, co-immunoprecipitation, Hsp90 inhibitor treatment, genetic mutant analysis, U6 snRNA quantification, splicing analysis","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP and genetic analysis in Arabidopsis (plant ortholog context), multiple methods but single organism/lab","pmids":["32396196"],"is_preprint":false},{"year":2025,"finding":"Using colocalization single-molecule spectroscopy, Lsm2-8 association with unprocessed U6 snRNA is highly dependent on Prp24, whereas 3'-end-processed U6 (bearing a 3'-phosphate) can rapidly recruit Lsm2-8 in the absence of Prp24; Prp24 promotes both recruitment and retention of Lsm2-8; this reveals a kinetic selection mechanism by which 3'-end modification and Prp24 coordinate efficient U6 snRNP assembly.","method":"Colocalization single-molecule spectroscopy (CoSMoS), in vitro reconstitution with modified and unmodified RNAs","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — single-molecule kinetic analysis with reconstituted components and defined RNA modifications","pmids":["40216252"],"is_preprint":false},{"year":2025,"finding":"Club cell-specific knockout of Lsm2 in mice leads to a significant reduction in the Club cell population (particularly Chia1+/Crb1+ cells) and subsequent reduction in ciliated epithelial cells, exacerbating lung injury and inflammation caused by cigarette smoke exposure; in vitro, knockdown of Lsm2 in 16HBE cells significantly reduces cell viability.","method":"Club cell-specific conditional knockout in mice, single-nucleus RNA sequencing, multiplexed immunohistochemistry, in vitro siRNA knockdown with cell viability assay","journal":"Respiratory research","confidence":"Medium","confidence_rationale":"Tier 2 — cell-type specific KO with snRNA-seq phenotyping, but mechanism linking Lsm2 RNA function to Club cell proliferation not yet defined","pmids":["40022153"],"is_preprint":false}],"current_model":"LSM2 is a core subunit of two mutually exclusive heteroheptameric complexes — the nuclear Lsm2-8 ring and the cytoplasmic Lsm1-7 ring — whose distinct RNA specificities are structurally determined: Lsm2-8 recognizes the unique 2',3'-cyclic phosphate of U6 snRNA to stabilize U6, retain it in the nucleus, enable U4/U6 duplex formation, and target nuclear RNAs for decapping, while Lsm1-7 binds oligouridylate tracts with terminal purines to activate cytoplasmic mRNA decapping via Pat1 (bridged through Lsm2 and Lsm3); in addition, the Lsm2-8 complex mediates post-transcriptional silencing of H3K27me3-marked heterochromatic genes through XRN-2-dependent RNA decay, and its assembly is kinetically governed by 3'-end RNA modification and Prp24."},"narrative":{"teleology":[{"year":1999,"claim":"The initial biochemical characterization established that human LSm proteins, including LSm2, assemble into a doughnut-shaped heptameric ring that binds the 3′ U-tract of U6 snRNA and facilitates U4/U6 duplex formation, defining LSm2 as a spliceosomal assembly factor.","evidence":"Purified recombinant complex analyzed by EM, in vitro RNA binding, and immunoprecipitation","pmids":["10523320"],"confidence":"High","gaps":["Stoichiometry and order of subunits within the ring not resolved","Structural basis for selective recognition of U6 over other U-rich snRNAs unknown"]},{"year":2001,"claim":"Genetic studies in yeast showed that Lsm2 and Lsm4 directly contact Lsm8 within the nuclear ring, and that the Lsm2-8 complex acts redundantly with La protein to stabilize nascent U6 snRNA, establishing the ring topology and functional redundancy in U6 biogenesis.","evidence":"Allele-specific suppressor analysis and snRNP level quantification in yeast","pmids":["11333229"],"confidence":"High","gaps":["Whether Lsm2-Lsm8 interaction is direct or mediated through Lsm4 not distinguished biochemically","Mechanism of La/Lsm redundancy not defined"]},{"year":2002,"claim":"Demonstration that LSm1-7 (but not LSm8) colocalizes with decapping enzymes in cytoplasmic P-bodies, while LSm2-8 is nuclear, resolved the long-standing question of how shared LSm2-7 subunits partition between two functionally distinct complexes.","evidence":"Immunofluorescence, FRET, and dominant-negative mutagenesis in human cells","pmids":["12515382"],"confidence":"High","gaps":["Mechanism controlling competitive assembly of Lsm1-7 vs Lsm2-8 not yet identified","Whether P-body localization is required for decapping function unclear"]},{"year":2004,"claim":"Two parallel discoveries expanded LSm2 functions: the nuclear Lsm2-8 complex was shown to target nuclear-restricted mRNAs for decapping and 5′ degradation, and an Lsm2-7 sub-complex was found to associate with box H/ACA snoRNAs in nucleoli, indicating roles beyond U6 snRNA.","evidence":"UV crosslinking and RNA stability assays in yeast export mutants; in vitro reconstitution and sequential IP for snoRNP association","pmids":["15485930","15075370"],"confidence":"High","gaps":["Substrates and specificity determinants for nuclear mRNA decapping by Lsm2-8 not defined","Functional consequence of Lsm2-7 association with snoRNAs not established"]},{"year":2007,"claim":"Systematic deletion and localization studies established that the intact Lsm2-8 ring is required for nuclear retention of U6 snRNA, and that Lsm1 and Lsm8 compete for shared Lsm2-7 subunits, with stress shifting the equilibrium toward cytoplasmic Lsm1-7 assembly.","evidence":"In situ hybridization of U6 in yeast lsm deletion strains; overexpression/depletion with fluorescence imaging","pmids":["17251193","18029398"],"confidence":"High","gaps":["Signal or modification that triggers stress-dependent redistribution not identified","Whether U6 mislocalization upon Lsm loss is due to export or degradation not fully resolved"]},{"year":2011,"claim":"The crystal structure of the LSm5-6-7 sub-complex revealed a canonical Sm-fold hexameric ring that serves as an assembly intermediate, with NMR confirming LSm2-3 incorporation to form the full ring, resolving the assembly pathway.","evidence":"X-ray crystallography at 2.5 Å, NMR spectroscopy, pull-down assays","pmids":["22001694"],"confidence":"High","gaps":["Full heptameric ring structure with RNA not yet available at this point","Kinetic control of assembly intermediate progression not addressed"]},{"year":2013,"claim":"A crystal structure of the Lsm2-3–Pat1C complex showed that Lsm2 and Lsm3 bridge Pat1 to the Lsm1-7 ring, and this sub-complex is sufficient to stimulate mRNA decapping, answering how the decapping activator is recruited.","evidence":"Crystal structure, in vitro decapping assay, structure-based mutagenesis validated in vivo in yeast","pmids":["24247251"],"confidence":"High","gaps":["Whether Pat1-Lsm2/3 interaction is regulated or constitutive unknown","Structural basis for full Lsm1-7-Pat1 heptameric complex not resolved"]},{"year":2017,"claim":"Discovery that Pat1b forms a nuclear complex with Lsm2-8 bound to U6 snRNA and SART3 in Cajal bodies extended the Pat1–LSm paradigm to nuclear splicing regulation in human cells, linking Pat1b depletion to alternative splicing defects.","evidence":"Co-immunoprecipitation, immunofluorescence, RNAi, and RNA-seq in human cells","pmids":["28768202"],"confidence":"High","gaps":["Molecular mechanism by which Pat1b-Lsm2-8 influences splice site selection not defined","Whether Pat1b competes with Prp24 for Lsm2-8 binding unknown"]},{"year":2018,"claim":"Structure-guided mutagenesis identified Lsm2-R63 as a critical U6-contacting residue, and demonstrated that U6 snRNA overexpression rescues lethality of all Lsm2-8 subunit deletions, proving that the sole essential function of the Lsm2-8 ring in yeast is U6 snRNA support.","evidence":"Alanine scanning across 235 pairwise combinations, high-copy suppressor analysis in yeast","pmids":["29615482"],"confidence":"High","gaps":["Whether U6 support is the sole essential function in metazoans not tested","Contribution of non-essential Lsm2-8 functions (nuclear decapping, snoRNA association) to fitness unclear"]},{"year":2020,"claim":"Three key advances: cryo-EM structures revealed that 2′,3′-cyclic phosphate recognition discriminates Lsm2-8 from Lsm1-7 RNA selectivity; the Lsm2-8 complex was shown to silence H3K27me3-marked heterochromatic genes via XRN-2; and prefoldins were identified as Hsp90-dependent chaperones for Lsm2-8 assembly in plants.","evidence":"Four high-resolution cryo-EM structures with RNA-binding assays; genetic epistasis with xrn-2 and ChIP in C. elegans; co-IP and Hsp90 inhibitor studies in Arabidopsis","pmids":["32518066","32251399","32396196"],"confidence":"High","gaps":["Whether cyclic phosphate recognition by Lsm2-8 is conserved in metazoans at structural level not confirmed","How Lsm2-8 is recruited specifically to H3K27me3-target transcripts unknown","Whether the PFD-Hsp90 axis for Lsm2-8 assembly operates in animals not tested"]},{"year":2025,"claim":"Single-molecule kinetics revealed that 3′-end processing of U6 and Prp24 cooperatively control Lsm2-8 assembly, and a mouse conditional knockout demonstrated that Lsm2 is essential for Club cell maintenance and lung epithelial homeostasis.","evidence":"CoSMoS with reconstituted components and defined RNA modifications; Club cell-specific Lsm2 knockout in mice with snRNA-seq and immunohistochemistry","pmids":["40216252","40022153"],"confidence":"High","gaps":["Whether Prp24-dependent kinetic selection operates in human cells not shown","Mechanistic link between Lsm2 RNA processing functions and Club cell survival not defined"]},{"year":null,"claim":"Major open questions include the structural basis of full Lsm1-7-Pat1 and Lsm2-8-Pat1b holo-complexes, how Lsm2-8 is recruited to heterochromatic transcripts, whether the sole-essential-function paradigm for U6 support extends to metazoan systems, and the molecular mechanism linking Lsm2 loss to epithelial cell fate decisions.","evidence":"","pmids":[],"confidence":"Low","gaps":["No full heptameric Lsm1-7-Pat1 or Lsm2-8-Pat1b complex structure","Mechanism of Lsm2-8 targeting to H3K27me3-marked transcripts unknown","Essential function of Lsm2-8 in metazoans not genetically delineated as in yeast"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[0,3,4,10,11,14]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,7,8]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[2,3,5,6,9]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[2,8]},{"term_id":"GO:0005730","term_label":"nucleolus","supporting_discovery_ids":[4]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[0,1,3,4,5,8,10,11,12,14]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[9,13]}],"complexes":["LSm2-8 heptameric ring","LSm1-7 heptameric ring","LSm2-3-Pat1C complex","U4/U6.U5 tri-snRNP"],"partners":["LSM8","LSM3","LSM4","PAT1B","SART3","PRP24","LSM1"],"other_free_text":[]},"mechanistic_narrative":"LSM2 is a core subunit of two functionally distinct heteroheptameric Sm-like (LSm) rings—the nuclear LSm2-8 complex and the cytoplasmic LSm1-7 complex—that govern RNA fate through U6 snRNA stabilization, pre-mRNA splicing, and mRNA decapping. In the nucleus, the LSm2-8 ring binds the 3′-terminal oligo(U) tract of U6 snRNA, with specificity conferred by recognition of the 2′,3′-cyclic phosphate end, and assembly kinetics governed by Prp24 and 3′-end RNA processing; the intact ring is essential for U6 nuclear retention, U4/U6 duplex formation, and targeting of nuclear RNAs for decapping [PMID:10523320, PMID:17251193, PMID:29615482, PMID:32518066, PMID:40216252]. LSm2 and LSm3 additionally bridge the Pat1 decapping activator to the LSm1-7 ring, directly stimulating cytoplasmic mRNA decapping [PMID:24247251, PMID:12515382]. Beyond canonical RNA processing, the LSm2-8 complex mediates post-transcriptional silencing of H3K27me3-marked heterochromatic genes through XRN-2-dependent transcript degradation [PMID:32251399]."},"prefetch_data":{"uniprot":{"accession":"Q9Y333","full_name":"U6 snRNA-associated Sm-like protein LSm2","aliases":["Protein G7b","Small nuclear ribonuclear protein D homolog","snRNP core Sm-like protein Sm-x5"],"length_aa":95,"mass_kda":10.8,"function":"Plays a role in pre-mRNA splicing as component of the U4/U6-U5 tri-snRNP complex that is involved in spliceosome assembly, and as component of the precatalytic spliceosome (spliceosome B complex) (PubMed:28781166). The heptameric LSM2-8 complex binds specifically to the 3'-terminal U-tract of U6 snRNA (PubMed:10523320)","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/Q9Y333/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/LSM2","classification":"Common Essential","n_dependent_lines":1208,"n_total_lines":1208,"dependency_fraction":1.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"SNRPF","stoichiometry":4.0},{"gene":"CAPZB","stoichiometry":0.2},{"gene":"CLNS1A","stoichiometry":0.2},{"gene":"CLTA","stoichiometry":0.2},{"gene":"CLTB","stoichiometry":0.2},{"gene":"CPSF6","stoichiometry":0.2},{"gene":"DDX21","stoichiometry":0.2},{"gene":"PSPC1","stoichiometry":0.2},{"gene":"RBM39","stoichiometry":0.2},{"gene":"RBM42","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/LSM2","total_profiled":1310},"omim":[{"mim_id":"621191","title":"LEUKODYSTROPHY AND CEREBELLAR ATROPHY; LDCA","url":"https://www.omim.org/entry/621191"},{"mim_id":"611684","title":"SPLICEOSOME-ASSOCIATED FACTOR 3, U4/U6 RECYCLING PROTEIN; SART3","url":"https://www.omim.org/entry/611684"},{"mim_id":"607288","title":"LSM8 PROTEIN; LSM8","url":"https://www.omim.org/entry/607288"},{"mim_id":"607287","title":"LSM7 PROTEIN; LSM7","url":"https://www.omim.org/entry/607287"},{"mim_id":"607286","title":"LSM6 PROTEIN; LSM6","url":"https://www.omim.org/entry/607286"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoplasm","reliability":"Enhanced"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/LSM2"},"hgnc":{"alias_symbol":["G7b","YBL026W"],"prev_symbol":["C6orf28"]},"alphafold":{"accession":"Q9Y333","domains":[{"cath_id":"2.30.30.100","chopping":"1-95","consensus_level":"medium","plddt":94.7314,"start":1,"end":95}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y333","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y333-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y333-F1-predicted_aligned_error_v6.png","plddt_mean":94.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=LSM2","jax_strain_url":"https://www.jax.org/strain/search?query=LSM2"},"sequence":{"accession":"Q9Y333","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9Y333.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9Y333/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y333"}},"corpus_meta":[{"pmid":"11333229","id":"PMC_11333229","title":"Multiple functional interactions between components of the Lsm2-Lsm8 complex, U6 snRNA, and the yeast La protein.","date":"2001","source":"Genetics","url":"https://pubmed.ncbi.nlm.nih.gov/11333229","citation_count":65,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"15485930","id":"PMC_15485930","title":"Nuclear pre-mRNA decapping and 5' degradation in yeast require the Lsm2-8p complex.","date":"2004","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/15485930","citation_count":57,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"28482101","id":"PMC_28482101","title":"Environment-dependent regulation of spliceosome activity by the LSM2-8 complex in Arabidopsis.","date":"2017","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/28482101","citation_count":43,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"15075370","id":"PMC_15075370","title":"An Lsm2-Lsm7 complex in Saccharomyces cerevisiae associates with the small nucleolar RNA snR5.","date":"2004","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/15075370","citation_count":37,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"24247251","id":"PMC_24247251","title":"Lsm2 and Lsm3 bridge the interaction of the Lsm1-7 complex with Pat1 for decapping activation.","date":"2013","source":"Cell research","url":"https://pubmed.ncbi.nlm.nih.gov/24247251","citation_count":35,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"17251193","id":"PMC_17251193","title":"The Lsm2-8 complex determines nuclear localization of the spliceosomal U6 snRNA.","date":"2007","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/17251193","citation_count":33,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"32518066","id":"PMC_32518066","title":"Molecular basis for the distinct cellular functions of the Lsm1-7 and Lsm2-8 complexes.","date":"2020","source":"RNA (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/32518066","citation_count":31,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"28768202","id":"PMC_28768202","title":"Dual RNA Processing Roles of Pat1b via Cytoplasmic Lsm1-7 and Nuclear Lsm2-8 Complexes.","date":"2017","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/28768202","citation_count":28,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"18029398","id":"PMC_18029398","title":"Requirements for nuclear localization of the Lsm2-8p complex and competition between nuclear and cytoplasmic Lsm complexes.","date":"2007","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/18029398","citation_count":26,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"32251399","id":"PMC_32251399","title":"LSM2-8 and XRN-2 contribute to the silencing of H3K27me3-marked genes through targeted RNA decay.","date":"2020","source":"Nature cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/32251399","citation_count":19,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"32396196","id":"PMC_32396196","title":"Prefoldins contribute to maintaining the levels of the spliceosome LSM2-8 complex through Hsp90 in Arabidopsis.","date":"2020","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/32396196","citation_count":19,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"22001694","id":"PMC_22001694","title":"Structure of the LSm657 complex: an assembly intermediate of the LSm1-7 and LSm2-8 rings.","date":"2011","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/22001694","citation_count":15,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"36016928","id":"PMC_36016928","title":"The cytoplasmic LSm1-7 and nuclear LSm2-8 complexes exert opposite effects on Hepatitis B virus biosynthesis and interferon responses.","date":"2022","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/36016928","citation_count":8,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"29615482","id":"PMC_29615482","title":"Defining essential elements and genetic interactions of the yeast Lsm2-8 ring and demonstration that essentiality of Lsm2-8 is bypassed via overexpression of U6 snRNA or the U6 snRNP subunit Prp24.","date":"2018","source":"RNA (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/29615482","citation_count":8,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"37612479","id":"PMC_37612479","title":"The mechanism of LSM2 in the progression of live hepatocellular carcinoma was analyzed based on bioinformatics.","date":"2023","source":"Medical oncology (Northwood, London, England)","url":"https://pubmed.ncbi.nlm.nih.gov/37612479","citation_count":5,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"40365337","id":"PMC_40365337","title":"LSM2 drives glioma progression through alternative splicing dysregulation: a multi-omics approach to identify a potential therapeutic target.","date":"2025","source":"Frontiers in oncology","url":"https://pubmed.ncbi.nlm.nih.gov/40365337","citation_count":2,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"40022153","id":"PMC_40022153","title":"Lsm2 is critical to club cell proliferation and its inhibition aggravates COPD progression.","date":"2025","source":"Respiratory research","url":"https://pubmed.ncbi.nlm.nih.gov/40022153","citation_count":0,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"40216252","id":"PMC_40216252","title":"RNA modifications and Prp24 coordinate Lsm2-8 binding dynamics during S. cerevisiae U6 snRNP assembly.","date":"2025","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/40216252","citation_count":0,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"40060616","id":"PMC_40060616","title":"RNA Modifications and Prp24 Coordinate Lsm2-8 Binding Dynamics during S. cerevisiae U6 snRNP Assembly.","date":"2025","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/40060616","citation_count":0,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":null,"id":"bio_10.1101_2024.08.23.609445","title":"Recontextualizing Eukaryogenesis via Computational Analysis of RNA Processing in 16,449 Archaeal Genomes","date":"2024-08-24","source":"bioRxiv","url":"https://doi.org/10.1101/2024.08.23.609445","citation_count":0,"is_preprint":true,"source_track":"pubmed_title"},{"pmid":null,"id":"bio_10.1101_2025.02.25.639938","title":"RNA Modifications and Prp24 Coordinate Lsm2-8 Binding Dynamics during <i>S. cerevisiae</i> U6 snRNP Assembly","date":"2025-02-27","source":"bioRxiv","url":"https://doi.org/10.1101/2025.02.25.639938","citation_count":0,"is_preprint":true,"source_track":"pubmed_title"},{"pmid":"16189514","id":"PMC_16189514","title":"Towards a proteome-scale map of the human protein-protein interaction network.","date":"2005","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/16189514","citation_count":2090,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"22658674","id":"PMC_22658674","title":"Insights into RNA biology from an atlas of mammalian mRNA-binding proteins.","date":"2012","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/22658674","citation_count":1718,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"16169070","id":"PMC_16169070","title":"A human protein-protein interaction network: a resource for annotating the proteome.","date":"2005","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/16169070","citation_count":1704,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"12477932","id":"PMC_12477932","title":"Generation and initial analysis of more than 15,000 full-length human and mouse cDNA sequences.","date":"2002","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/12477932","citation_count":1479,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"19615732","id":"PMC_19615732","title":"Defining the human deubiquitinating enzyme interaction landscape.","date":"2009","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/19615732","citation_count":1282,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"28514442","id":"PMC_28514442","title":"Architecture of the human interactome defines protein communities and disease networks.","date":"2017","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/28514442","citation_count":1085,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"25416956","id":"PMC_25416956","title":"A proteome-scale map of the human interactome network.","date":"2014","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/25416956","citation_count":977,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"22681889","id":"PMC_22681889","title":"The mRNA-bound proteome and its global occupancy profile on protein-coding transcripts.","date":"2012","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/22681889","citation_count":973,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"15592455","id":"PMC_15592455","title":"Immunoaffinity profiling of tyrosine phosphorylation in cancer cells.","date":"2004","source":"Nature biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/15592455","citation_count":916,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"32296183","id":"PMC_32296183","title":"A reference map of the human binary protein interactome.","date":"2020","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/32296183","citation_count":849,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"12226669","id":"PMC_12226669","title":"Comprehensive proteomic analysis of the human spliceosome.","date":"2002","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/12226669","citation_count":725,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"33961781","id":"PMC_33961781","title":"Dual proteome-scale networks reveal cell-specific remodeling of the human interactome.","date":"2021","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/33961781","citation_count":705,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"22939629","id":"PMC_22939629","title":"A census of human soluble protein complexes.","date":"2012","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/22939629","citation_count":689,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"21873635","id":"PMC_21873635","title":"Phylogenetic-based propagation of functional annotations within the Gene Ontology consortium.","date":"2011","source":"Briefings in bioinformatics","url":"https://pubmed.ncbi.nlm.nih.gov/21873635","citation_count":656,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"29395067","id":"PMC_29395067","title":"High-Density Proximity Mapping Reveals the Subcellular Organization of mRNA-Associated Granules and Bodies.","date":"2018","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/29395067","citation_count":580,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"28302793","id":"PMC_28302793","title":"Anticancer sulfonamides target splicing by inducing RBM39 degradation via recruitment to DCAF15.","date":"2017","source":"Science (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/28302793","citation_count":533,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"15489334","id":"PMC_15489334","title":"The status, quality, and expansion of the NIH full-length cDNA project: the Mammalian Gene Collection (MGC).","date":"2004","source":"Genome research","url":"https://pubmed.ncbi.nlm.nih.gov/15489334","citation_count":438,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"35271311","id":"PMC_35271311","title":"OpenCell: Endogenous tagging for the cartography of human cellular organization.","date":"2022","source":"Science (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/35271311","citation_count":432,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"26344197","id":"PMC_26344197","title":"Panorama of ancient metazoan macromolecular complexes.","date":"2015","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/26344197","citation_count":407,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"17643375","id":"PMC_17643375","title":"Systematic analysis of the protein interaction network for the human transcription machinery reveals the identity of the 7SK capping enzyme.","date":"2007","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/17643375","citation_count":367,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"14685174","id":"PMC_14685174","title":"Splicing double: insights from the second spliceosome.","date":"2003","source":"Nature reviews. Molecular cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/14685174","citation_count":329,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"22365833","id":"PMC_22365833","title":"Dynamic protein-protein interaction wiring of the human spliceosome.","date":"2012","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/22365833","citation_count":318,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"12515382","id":"PMC_12515382","title":"The human LSm1-7 proteins colocalize with the mRNA-degrading enzymes Dcp1/2 and Xrnl in distinct cytoplasmic foci.","date":"2002","source":"RNA (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/12515382","citation_count":303,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"11991638","id":"PMC_11991638","title":"Purification and characterization of native spliceosomes suitable for three-dimensional structural analysis.","date":"2002","source":"RNA (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/11991638","citation_count":301,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"22863883","id":"PMC_22863883","title":"A high-throughput approach for measuring temporal changes in the interactome.","date":"2012","source":"Nature methods","url":"https://pubmed.ncbi.nlm.nih.gov/22863883","citation_count":273,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"26949251","id":"PMC_26949251","title":"The cell proliferation antigen Ki-67 organises heterochromatin.","date":"2016","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/26949251","citation_count":265,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"10523320","id":"PMC_10523320","title":"A doughnut-shaped heteromer of human Sm-like proteins binds to the 3'-end of U6 snRNA, thereby facilitating U4/U6 duplex formation in vitro.","date":"1999","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/10523320","citation_count":260,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"10601333","id":"PMC_10601333","title":"Gemin3: A novel DEAD box protein that interacts with SMN, the spinal muscular atrophy gene product, and is a component of gems.","date":"1999","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/10601333","citation_count":235,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"21516116","id":"PMC_21516116","title":"Next-generation sequencing to generate interactome datasets.","date":"2011","source":"Nature methods","url":"https://pubmed.ncbi.nlm.nih.gov/21516116","citation_count":200,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"28781166","id":"PMC_28781166","title":"Cryo-EM Structure of a Pre-catalytic Human Spliceosome Primed for Activation.","date":"2017","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/28781166","citation_count":199,"is_preprint":false,"source_track":"gene2pubmed"}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":11763,"output_tokens":3098,"usd":0.040879},"stage2":{"model":"claude-opus-4-6","input_tokens":6444,"output_tokens":2777,"usd":0.152468},"total_usd":0.443995,"stage1_batch_id":"msgbatch_01Mgbec4vM6c9vXht7JVJzss","stage2_batch_id":"msgbatch_01JkuuH5RB2BdJNsgnhjbC6s","note":"batch pricing = 50% of standard","round2_stage1":{"model":"claude-sonnet-4-6","input_tokens":22604,"output_tokens":4316,"usd":0.066276},"round2_rules_fired":"R3","round2_stage2":{"model":"claude-opus-4-6","input_tokens":7993,"output_tokens":3318,"usd":0.184372}},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2001,\n      \"finding\": \"LSM2 and LSM4 act as allele-specific suppressors of mutations in Lsm8p, and overexpression of LSM2 increases levels of both Lsm8p and U6 snRNPs, indicating that Lsm2p and Lsm4p contact Lsm8p in the Lsm2-8 ring and act redundantly with the La protein (Lhp1p) to stabilize nascent U6 snRNA.\",\n      \"method\": \"Genetic suppressor analysis, overexpression experiments, snRNP level measurements in yeast\",\n      \"journal\": \"Genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with multiple alleles, replicated across multiple LSM gene deletions\",\n      \"pmids\": [\"11333229\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The nuclear Lsm2-8p complex targets nuclear RNA substrates (mature mRNAs trapped in nucleus and pre-mRNA degradation intermediates) for decapping and 5' degradation; Lsm8p UV cross-links directly to nuclear poly(A)+ RNA, and nuclear mRNA decay does not involve incremental deadenylation.\",\n      \"method\": \"UV cross-linking, genetic deletion of LSM subunits, mRNA stability assays, northern blotting in yeast\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct UV cross-linking plus genetic KO with defined RNA substrate phenotype\",\n      \"pmids\": [\"15485930\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"An Lsm2-Lsm7 subcomplex (lacking Lsm8) associates with the box H/ACA snoRNA snR5; in vitro reconstitution showed that the 3' end of snR5 is critical for Lsm protein recognition, and Lsm proteins are present in nucleoli where they may contribute to snoRNA biogenesis or function without being required for snR5-guided pseudouridylation.\",\n      \"method\": \"In vitro reconstitution of Lsm-snR5 binding, glycerol gradient sedimentation, sequential immunoprecipitation, fluorescence microscopy showing nucleolar localization\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro reconstitution plus sequential IP and functional (pseudouridylation) assays\",\n      \"pmids\": [\"15075370\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The complete Lsm2-8 complex is required for nuclear accumulation of U6 snRNA in yeast; Lsm8p plays the crucial role in nuclear localization of the complex, and its nuclear localization is most strongly influenced by Lsm2p and Lsm4p (its presumed neighbors in the ring).\",\n      \"method\": \"Fluorescence microscopy of GFP-tagged Lsm proteins, U6 snRNA localization assays in deletion strains\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct localization experiments with genetic deletions and functional consequence (U6 mislocalization)\",\n      \"pmids\": [\"17251193\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Lsm1p and Lsm8p compete for incorporation into cytoplasmic vs. nuclear Lsm complexes, respectively; overexpression or depletion of Lsm1p or Lsm8p shifts localization of shared Lsm proteins between compartments, and Lsm proteins shift from nucleus to cytoplasm under stress conditions.\",\n      \"method\": \"Overexpression and depletion experiments, fluorescence microscopy, localization assays in yeast\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization with functional overexpression/depletion, single lab\",\n      \"pmids\": [\"18029398\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"LSM5, LSM6, and LSM7 form a hexameric LSm657-657 ring assembly intermediate with canonical Sm fold; this complex can incorporate LSm2-3 to assemble toward native LSm1-7 and LSm2-8 rings, defining an ordered assembly pathway.\",\n      \"method\": \"2.5 Å crystal structure, high-resolution NMR spectroscopy in solution, pull-down experiments\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus NMR and pull-down validation\",\n      \"pmids\": [\"22001694\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Lsm2 and Lsm3 bridge the interaction between the C-terminus of Pat1 (Pat1C) and the Lsm1-7 complex; the crystal structure of the Lsm2-3-Pat1C complex shows three Pat1C molecules surrounding a Lsm2-3 heptameric ring, and the Lsm2-3-Pat1C complex stimulates mRNA decapping in vitro; structure-based mutagenesis confirmed the functional importance of these contacts in vivo.\",\n      \"method\": \"Crystal structure of Lsm2-3-Pat1C complex, in vitro decapping assay, RNA-binding assays, structure-based mutagenesis with in vivo validation\",\n      \"journal\": \"Cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus in vitro decapping assay plus mutagenesis validated in vivo\",\n      \"pmids\": [\"24247251\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Pat1b forms a nuclear complex with the Lsm2-8 heptamer that binds U6 snRNA, and this complex connects to SART3 and additional U4/U6.U5 tri-snRNP components in Cajal bodies; Pat1b depletion causes >180 alternative splicing events (predominantly exon skipping at weak donor sites), demonstrating a role for the Pat1b/Lsm2-8 complex in pre-mRNA splicing.\",\n      \"method\": \"Co-immunoprecipitation, immunofluorescence, RNAi knockdown, RNA sequencing for alternative splicing analysis in human cells\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP plus RNA-seq with functional knockdown, multiple orthogonal methods\",\n      \"pmids\": [\"28768202\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Structure-guided mutational analysis identified that Lsm3-R69A and Lsm2-R63A (RNA-binding residues contacting the 3'-terminal UUU of U6) are critical for function; overexpression of U6 snRNA rescues lethal deletions of lsm2, lsm3, lsm4, lsm5, and lsm8, demonstrating that the only essential function of the Lsm2-8 ring is to abet U6 snRNA.\",\n      \"method\": \"Alanine scanning mutagenesis of 39 amino acids, yeast growth assays, U6 snRNA overexpression rescue of 235 pairwise deletion combinations\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — systematic structure-guided mutagenesis plus epistasis rescue experiments across comprehensive deletion matrix\",\n      \"pmids\": [\"29615482\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Four high-resolution structures of Lsm2-8 bound to RNA reveal that the unique 2',3'-cyclic phosphate end of U6 snRNA is a prime determinant of Lsm2-8 specificity; in contrast, Lsm1-7 strongly discriminates against cyclic phosphates and binds oligouridylate tracts with terminal purines, with Lsm5 uniquely recognizing purine bases; Lsm1-7 loads onto RNA from the 3' end with a gated mechanism for internal site access.\",\n      \"method\": \"High-resolution cryo-EM/crystal structures of Lsm complexes bound to RNA, biochemical RNA-binding assays, functional analysis of Lsm1 carboxy-terminal deletion\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple high-resolution structures with biochemical validation of specificity determinants\",\n      \"pmids\": [\"32518066\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"In C. elegans, the LSM2-8 complex contributes selectively to repression of H3K27me3-marked heterochromatic genes by degrading their transcripts through the XRN-2 exoribonuclease; disruption of LSM2-8 stabilizes these mRNAs and coincides with localized reduction in H3K27me3, independent of H3K9 methylation.\",\n      \"method\": \"Genetic knockdown of LSM-8 and XRN-2, mRNA stability assays, chromatin immunoprecipitation for H3K27me3 in C. elegans\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis between LSM2-8 and XRN-2 with defined molecular phenotype (mRNA stabilization) and chromatin readout\",\n      \"pmids\": [\"32251399\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Using colocalization single-molecule spectroscopy, Lsm2-8 association with unprocessed U6 snRNA is highly dependent on Prp24, whereas 3'-end processed U6 snRNA (bearing a 3' phosphate) can rapidly recruit Lsm2-8 in the absence of Prp24; Prp24 promotes both recruitment and retention of Lsm2-8, suggesting kinetic selection of Lsm2-8 for modified or Prp24-bound U6 during snRNP assembly.\",\n      \"method\": \"Colocalization single-molecule spectroscopy (CoSMoS), kinetic analysis of Lsm2-8/U6 snRNA assembly in yeast\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — single-molecule reconstitution with kinetic dissection of assembly pathway\",\n      \"pmids\": [\"40216252\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"LSM2 is a core subunit of two distinct heteroheptameric ring complexes: the nuclear Lsm2-8 complex, which binds the 2',3'-cyclic phosphate 3' end of U6 snRNA to stabilize it, retain it in the nucleus, and regulate its snRNP assembly kinetics in cooperation with Prp24, and also targets nuclear RNAs (including heterochromatic H3K27me3-marked transcripts) for decapping and 5' degradation via XRN-2; and the cytoplasmic Lsm1-7 complex, where Lsm2 and Lsm3 bridge the interaction with Pat1 to activate mRNA decapping, with the two complexes competing for shared subunits to partition RNA processing between nuclear and cytoplasmic compartments.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1999,\n      \"finding\": \"Human LSm proteins (including LSm2) form a stable doughnut-shaped heteromeric complex that binds specifically to the 3'-terminal U-tract of U6 snRNA and facilitates U4/U6 RNA duplex formation in vitro; the complex does not bind the U-rich Sm sites of intact U1, U2, U4, or U5 snRNAs.\",\n      \"method\": \"Protein purification, electron microscopy, in vitro RNA binding assay, immunoprecipitation\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted complex, EM structure, in vitro functional assay with specificity controls\",\n      \"pmids\": [\"10523320\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"In yeast, LSM2 and LSM4 (but not other LSM genes) act as allele-specific low-copy suppressors of mutations in Lsm8p; overexpression of LSM2 increases levels of both Lsm8p and U6 snRNPs, consistent with Lsm2p and Lsm4p directly contacting Lsm8p within the Lsm2-8 ring; the entire Lsm2-8 complex acts redundantly with La protein (Lhp1p) to stabilize nascent U6 snRNA.\",\n      \"method\": \"Genetic suppressor analysis, overexpression experiments, snRNP level quantification\",\n      \"journal\": \"Genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — allele-specific suppression and biochemical quantification, consistent model across multiple genetic tests\",\n      \"pmids\": [\"11333229\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Human LSm1-7 proteins (not LSm8) colocalize with mRNA-degrading enzymes Dcp1/2 and Xrn1 in discrete cytoplasmic foci (P-bodies); LSm8 is excluded from these foci, delineating distinct cytoplasmic (LSm1-7) and nuclear (LSm2-8) complexes; complex formation is required for enrichment in cytoplasmic foci.\",\n      \"method\": \"Subcellular localization by immunofluorescence, FRET, co-expression of wild-type and dominant-negative LSm mutants\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct localization with FRET validation and functional mutagenesis, clearly distinguishing LSm2-8 nuclear complex from LSm1-7\",\n      \"pmids\": [\"12515382\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The nuclear Lsm2-8p complex is required for decapping and 5' degradation of nucleus-restricted mRNAs and pre-mRNA degradation intermediates; Lsm8p (but not cytoplasmic Lsm1p) UV-crosslinks directly to nuclear poly(A)+ RNA, indicating the Lsm2-8p complex physically interacts with nuclear RNA substrates and targets them for decapping.\",\n      \"method\": \"UV crosslinking, genetic deletion analysis, RNA stability assays in yeast strains with nuclear mRNA export blocks\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct UV crosslinking combined with genetic epistasis and RNA stability measurements\",\n      \"pmids\": [\"15485930\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"A third Lsm complex consisting of Lsm2-Lsm7 (without Lsm1 or Lsm8) associates with the box H/ACA snoRNA snR5 in yeast; in vitro reconstitution shows the 3' end of snR5 is critical for Lsm protein recognition; this Lsm2-7 complex is partially distinct from the canonical snR5 box H/ACA protein complex and localizes to nucleoli, suggesting a nucleolar function for Lsm proteins in snoRNA biogenesis.\",\n      \"method\": \"In vitro reconstitution of RNA-protein binding, glycerol gradient sedimentation, sequential immunoprecipitation, subcellular fractionation/localization\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro reconstitution plus multiple orthogonal biochemical approaches\",\n      \"pmids\": [\"15075370\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The complete Lsm2-8 complex is required for nuclear accumulation of U6 snRNA in yeast; loss of any single Lsm2-8 subunit causes U6 mislocalization; La protein has a smaller, indirect effect on U6 localization consistent with a chaperone role in Lsm2-8 assembly rather than direct nuclear retention.\",\n      \"method\": \"In situ hybridization of U6 snRNA in lsm deletion strains, genetic analysis\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct RNA localization measurements across multiple deletion mutants with clear phenotypic readout\",\n      \"pmids\": [\"17251193\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Nuclear accumulation of Lsm proteins in yeast depends on complex formation; Lsm8p plays a crucial role in nuclear localization, with its own localization most strongly influenced by Lsm2p and Lsm4p (its presumed neighbors); Lsm1p and Lsm8p act competitively to partition the shared Lsm2-7 subunits between cytoplasmic and nuclear complexes, and stress shifts Lsm proteins from nucleus to cytoplasm.\",\n      \"method\": \"Overexpression and depletion experiments, subcellular localization by fluorescence microscopy in yeast\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic overexpression/depletion with direct imaging, showing competitive mechanism\",\n      \"pmids\": [\"18029398\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Crystal structure of the LSm5-6-7 (LSm657) assembly intermediate resolved at 2.5 Å reveals canonical Sm fold monomers arranged in a hexameric ring; NMR and pull-down experiments show that the LSm657 complex can incorporate LSm2-3 to assemble towards native LSm1-7 and LSm2-8 rings, identifying LSm657 as a functional building block on the assembly pathway.\",\n      \"method\": \"X-ray crystallography (2.5 Å), NMR spectroscopy, pull-down assays\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus NMR and pull-down validation of assembly intermediate\",\n      \"pmids\": [\"22001694\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Lsm2 and Lsm3 bridge the interaction between the C-terminus of Pat1 (Pat1C) and the Lsm1-7 complex; crystal structure of the Lsm2-3-Pat1C complex shows three Pat1C molecules surrounding a heptameric Lsm2-3 ring in an asymmetric arrangement; the Lsm2-3-Pat1C complex stimulates mRNA decapping in vitro to a similar extent as full Lsm1-7-Pat1C; structure-based mutagenesis confirmed that Lsm2-3–Pat1C interactions are required for decapping activation in vivo.\",\n      \"method\": \"Crystal structure determination, in vitro decapping assay, RNA-binding assay, structure-based mutagenesis, yeast in vivo decapping assays\",\n      \"journal\": \"Cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with reconstituted in vitro functional assay and in vivo mutagenesis validation\",\n      \"pmids\": [\"24247251\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In human cells, Pat1b forms a nuclear complex with the Lsm2-8 heptamer that binds U6 snRNA and interacts with SART3 and additional U4/U6.U5 tri-snRNP components in Cajal bodies; Pat1b depletion causes alternative splicing changes (exon skipping at weak donor sites) as well as upregulation of P-body-enriched mRNAs, demonstrating dual roles for Pat1b/Lsm2-8 in nuclear splicing and cytoplasmic mRNA decay via distinct complexes.\",\n      \"method\": \"Co-immunoprecipitation, immunofluorescence, RNAi knockdown, RNA sequencing\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP combined with RNA-seq and RNAi, multiple orthogonal methods\",\n      \"pmids\": [\"28768202\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Structure-guided mutagenesis of the yeast Lsm2-8 ring identifies Lsm3-R69A (lethal) and Lsm2-R63A (severe growth defect) as critical RNA-binding residues that contact the 3'-terminal UUU of U6 snRNA; lethal deletions of lsm2, lsm3, lsm4, lsm5, and lsm8 are all rescued by U6 snRNA overexpression, establishing that the sole essential function of the Lsm2-8 ring in yeast is to support U6 snRNA biogenesis/function.\",\n      \"method\": \"Alanine scanning mutagenesis, high-copy suppressor analysis, genetic rescue with U6 overexpression\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — structure-guided mutagenesis combined with rigorous genetic epistasis across 235 pairwise combinations\",\n      \"pmids\": [\"29615482\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"High-resolution cryo-EM structures of Lsm2-8 bound to RNA show that the unique 2',3'-cyclic phosphate end of U6 snRNA is a prime determinant of Lsm2-8 specificity; Lsm5 uniquely recognizes purine bases, explaining its divergent sequence; in contrast, Lsm1-7 strongly discriminates against cyclic phosphates and prefers oligouridylate tracts with terminal purines, revealing the molecular basis for the distinct RNA selectivities of the two complexes.\",\n      \"method\": \"Cryo-EM structure determination (four high-resolution structures), RNA-binding specificity assays\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple high-resolution cryo-EM structures with functional RNA-binding specificity characterization\",\n      \"pmids\": [\"32518066\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"In C. elegans somatic cells, the LSM2-8 complex contributes to silencing of H3K27me3-marked heterochromatic genes by targeting their transcripts for degradation via the XRN-2 exoribonuclease; disruption of LSM2-8 stabilizes these mRNAs and coincides with a localized reduction of H3K27me3 at sensitive loci; this pathway does not require H3K9 methylation, distinguishing it from other heterochromatic RNA degradation pathways.\",\n      \"method\": \"Genetic knockdown/knockout, RNA stability assays, chromatin immunoprecipitation for H3K27me3, epistasis with xrn-2\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with XRN-2, RNA stability measurements, and ChIP, replicated across reporters and endogenous genes\",\n      \"pmids\": [\"32251399\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"In Arabidopsis, prefoldins (PFDs) interact with LSM2-8 complex components and are required to maintain adequate levels of the complex; LSM8 protein is a client of Hsp90, and PFD4 mediates the interaction between LSM8 and Hsp90; loss of PFDs reduces LSM8 levels and U6 snRNA levels and alters pre-mRNA splicing, establishing a PFD-Hsp90-LSM2-8 axis for spliceosomal complex proteostasis.\",\n      \"method\": \"Co-expression analysis, co-immunoprecipitation, Hsp90 inhibitor treatment, genetic mutant analysis, U6 snRNA quantification, splicing analysis\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP and genetic analysis in Arabidopsis (plant ortholog context), multiple methods but single organism/lab\",\n      \"pmids\": [\"32396196\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Using colocalization single-molecule spectroscopy, Lsm2-8 association with unprocessed U6 snRNA is highly dependent on Prp24, whereas 3'-end-processed U6 (bearing a 3'-phosphate) can rapidly recruit Lsm2-8 in the absence of Prp24; Prp24 promotes both recruitment and retention of Lsm2-8; this reveals a kinetic selection mechanism by which 3'-end modification and Prp24 coordinate efficient U6 snRNP assembly.\",\n      \"method\": \"Colocalization single-molecule spectroscopy (CoSMoS), in vitro reconstitution with modified and unmodified RNAs\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — single-molecule kinetic analysis with reconstituted components and defined RNA modifications\",\n      \"pmids\": [\"40216252\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Club cell-specific knockout of Lsm2 in mice leads to a significant reduction in the Club cell population (particularly Chia1+/Crb1+ cells) and subsequent reduction in ciliated epithelial cells, exacerbating lung injury and inflammation caused by cigarette smoke exposure; in vitro, knockdown of Lsm2 in 16HBE cells significantly reduces cell viability.\",\n      \"method\": \"Club cell-specific conditional knockout in mice, single-nucleus RNA sequencing, multiplexed immunohistochemistry, in vitro siRNA knockdown with cell viability assay\",\n      \"journal\": \"Respiratory research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — cell-type specific KO with snRNA-seq phenotyping, but mechanism linking Lsm2 RNA function to Club cell proliferation not yet defined\",\n      \"pmids\": [\"40022153\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"LSM2 is a core subunit of two mutually exclusive heteroheptameric complexes — the nuclear Lsm2-8 ring and the cytoplasmic Lsm1-7 ring — whose distinct RNA specificities are structurally determined: Lsm2-8 recognizes the unique 2',3'-cyclic phosphate of U6 snRNA to stabilize U6, retain it in the nucleus, enable U4/U6 duplex formation, and target nuclear RNAs for decapping, while Lsm1-7 binds oligouridylate tracts with terminal purines to activate cytoplasmic mRNA decapping via Pat1 (bridged through Lsm2 and Lsm3); in addition, the Lsm2-8 complex mediates post-transcriptional silencing of H3K27me3-marked heterochromatic genes through XRN-2-dependent RNA decay, and its assembly is kinetically governed by 3'-end RNA modification and Prp24.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"LSM2 is a core subunit of two functionally distinct heteroheptameric Sm-like ring complexes — the nuclear Lsm2-8 and cytoplasmic Lsm1-7 — that partition RNA processing between compartments. In the Lsm2-8 complex, LSM2 directly contacts RNA through residue R63, recognizing the 2',3'-cyclic phosphate 3' end of U6 snRNA to stabilize it, retain it in the nucleus, and cooperate with Prp24 during snRNP assembly; the sole essential function of the Lsm2-8 ring in yeast is to support U6 snRNA [PMID:29615482, PMID:32518066, PMID:40216252]. In the cytoplasmic Lsm1-7 complex, LSM2 and LSM3 bridge the interaction with Pat1 to stimulate mRNA decapping [PMID:24247251]. The Lsm2-8 complex additionally targets heterochromatic H3K27me3-marked transcripts for 5' degradation via XRN-2, links to SART3 and U4/U6.U5 tri-snRNP components in Cajal bodies to regulate pre-mRNA splicing, and associates with snoRNAs [PMID:32251399, PMID:28768202, PMID:15075370].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Establishing that LSM2 directly contacts LSM8 in the Lsm2-8 ring and functions redundantly with the La protein to stabilize nascent U6 snRNA resolved the subunit topology and initial function of the nuclear Lsm ring.\",\n      \"evidence\": \"Genetic suppressor analysis and overexpression experiments measuring snRNP levels in yeast\",\n      \"pmids\": [\"11333229\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physical contact between Lsm2 and Lsm8 inferred from genetics, not yet confirmed structurally\", \"Mechanism by which Lsm2 stabilizes U6 not defined at atomic level\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Demonstrating that the nuclear Lsm2-8 complex targets nuclear RNA substrates for decapping and 5'-to-3' degradation, and that an Lsm2-7 subcomplex associates with box H/ACA snoRNAs in the nucleolus, expanded the functional repertoire beyond U6 snRNA.\",\n      \"evidence\": \"UV cross-linking, genetic deletions, mRNA stability assays, in vitro reconstitution of Lsm-snoRNA binding, sequential immunoprecipitation, and fluorescence microscopy in yeast\",\n      \"pmids\": [\"15485930\", \"15075370\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of snoRNA binding unclear since pseudouridylation was unaffected\", \"Identity of decapping enzyme recruited by Lsm2-8 in the nucleus not determined\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Showing that Lsm1 and Lsm8 compete for shared subunits including Lsm2 to partition them between cytoplasmic and nuclear complexes, and that Lsm2 and Lsm4 most strongly influence Lsm8 nuclear localization, defined the regulatory logic controlling Lsm complex compartmentalization.\",\n      \"evidence\": \"GFP-tagged Lsm protein localization, overexpression/depletion experiments, U6 snRNA localization assays in yeast deletion strains\",\n      \"pmids\": [\"17251193\", \"18029398\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signal or modification directing initial nuclear import of Lsm subunits unknown\", \"Stress-induced redistribution mechanism not molecularly defined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Solving the crystal structure of the Lsm5-6-7 hexameric assembly intermediate and showing it incorporates Lsm2-3 toward native ring formation defined an ordered assembly pathway for both Lsm1-7 and Lsm2-8 complexes.\",\n      \"evidence\": \"2.5 Å crystal structure, NMR spectroscopy, and pull-down experiments\",\n      \"pmids\": [\"22001694\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Chaperone or assembly factor requirements in vivo not addressed\", \"Rate-limiting step of ring closure not determined\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"The crystal structure of the Lsm2-3-Pat1C complex revealed that Lsm2 and Lsm3 serve as the critical bridge between the Lsm1-7 ring and the decapping activator Pat1, directly linking ring architecture to cytoplasmic mRNA decapping.\",\n      \"evidence\": \"Crystal structure, in vitro decapping assay, RNA-binding assays, structure-based mutagenesis validated in vivo\",\n      \"pmids\": [\"24247251\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Pat1 binding alters Lsm ring RNA selectivity not tested\", \"Structural basis for Pat1 exclusion from Lsm2-8 complex not determined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Discovery that Pat1b forms a nuclear complex with Lsm2-8 connected to SART3 and tri-snRNP components in Cajal bodies, and that its depletion causes widespread exon skipping, established a direct role for the Pat1b/Lsm2-8 complex in pre-mRNA splicing regulation in human cells.\",\n      \"evidence\": \"Co-immunoprecipitation, immunofluorescence, RNAi knockdown, and RNA-seq in human cells\",\n      \"pmids\": [\"28768202\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which Pat1b/Lsm2-8 promotes splice site recognition not determined\", \"Whether this function is conserved beyond mammals not tested\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Systematic mutagenesis identified Lsm2-R63 as a critical RNA-contact residue, and U6 overexpression rescued lethal Lsm deletions, proving that the only essential function of the Lsm2-8 ring is to support U6 snRNA.\",\n      \"evidence\": \"Alanine scanning of 39 residues, yeast growth assays, U6 overexpression rescue across 235 pairwise deletion combinations\",\n      \"pmids\": [\"29615482\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Non-essential functions (nuclear mRNA decay, snoRNA binding) not quantitatively assessed for fitness contribution\", \"Whether U6 rescue reflects stabilization, localization, or assembly not distinguished\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"High-resolution structures revealed that Lsm2-8 specifically recognizes the 2',3'-cyclic phosphate on U6 snRNA while Lsm1-7 discriminates against it, explaining how the two ring complexes achieve RNA substrate selectivity; separately, genetic studies showed Lsm2-8 selectively represses H3K27me3-marked heterochromatic transcripts through XRN-2-mediated degradation.\",\n      \"evidence\": \"Cryo-EM/crystal structures of Lsm complexes with RNA, biochemical binding assays; genetic epistasis of LSM-8 and XRN-2 with ChIP for H3K27me3 in C. elegans\",\n      \"pmids\": [\"32518066\", \"32251399\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How Lsm2-8 is recruited specifically to H3K27me3-marked transcripts unknown\", \"Whether cyclic phosphate recognition is regulated post-translationally not explored\", \"Structural basis for XRN-2 coupling to Lsm2-8 not determined\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Single-molecule kinetic analysis showed that Prp24 dramatically enhances Lsm2-8 recruitment to unprocessed U6 but is dispensable for 3'-processed U6, revealing a kinetic selection mechanism that couples U6 3'-end processing to snRNP assembly.\",\n      \"evidence\": \"Colocalization single-molecule spectroscopy (CoSMoS) with purified yeast components\",\n      \"pmids\": [\"40216252\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo validation of kinetic gating not performed\", \"Role of other cofactors (e.g. USPL1/Usb1) in timing of Lsm2-8 loading not addressed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How Lsm2-8 is selectively recruited to heterochromatic transcripts, how Pat1 binding is partitioned between nuclear and cytoplasmic Lsm complexes, and whether Lsm2-8 functions beyond U6 snRNA are physiologically important remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Recruitment mechanism of Lsm2-8 to H3K27me3-marked loci unknown\", \"Structural basis for Pat1 association with nuclear vs. cytoplasmic Lsm rings not determined\", \"Physiological relevance of snoRNA association not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [0, 2, 8, 9, 11]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [5, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 1, 3, 7]},\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [4, 6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [1, 8, 9, 10]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [7, 10]}\n    ],\n    \"complexes\": [\n      \"Lsm2-8 (nuclear)\",\n      \"Lsm1-7 (cytoplasmic)\",\n      \"Lsm1-7-Pat1\"\n    ],\n    \"partners\": [\n      \"LSM8\",\n      \"LSM4\",\n      \"LSM3\",\n      \"LSM1\",\n      \"PATL1\",\n      \"PRP24\",\n      \"SART3\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"LSM2 is a core subunit of two functionally distinct heteroheptameric Sm-like (LSm) rings—the nuclear LSm2-8 complex and the cytoplasmic LSm1-7 complex—that govern RNA fate through U6 snRNA stabilization, pre-mRNA splicing, and mRNA decapping. In the nucleus, the LSm2-8 ring binds the 3′-terminal oligo(U) tract of U6 snRNA, with specificity conferred by recognition of the 2′,3′-cyclic phosphate end, and assembly kinetics governed by Prp24 and 3′-end RNA processing; the intact ring is essential for U6 nuclear retention, U4/U6 duplex formation, and targeting of nuclear RNAs for decapping [PMID:10523320, PMID:17251193, PMID:29615482, PMID:32518066, PMID:40216252]. LSm2 and LSm3 additionally bridge the Pat1 decapping activator to the LSm1-7 ring, directly stimulating cytoplasmic mRNA decapping [PMID:24247251, PMID:12515382]. Beyond canonical RNA processing, the LSm2-8 complex mediates post-transcriptional silencing of H3K27me3-marked heterochromatic genes through XRN-2-dependent transcript degradation [PMID:32251399].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"The initial biochemical characterization established that human LSm proteins, including LSm2, assemble into a doughnut-shaped heptameric ring that binds the 3′ U-tract of U6 snRNA and facilitates U4/U6 duplex formation, defining LSm2 as a spliceosomal assembly factor.\",\n      \"evidence\": \"Purified recombinant complex analyzed by EM, in vitro RNA binding, and immunoprecipitation\",\n      \"pmids\": [\"10523320\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and order of subunits within the ring not resolved\", \"Structural basis for selective recognition of U6 over other U-rich snRNAs unknown\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Genetic studies in yeast showed that Lsm2 and Lsm4 directly contact Lsm8 within the nuclear ring, and that the Lsm2-8 complex acts redundantly with La protein to stabilize nascent U6 snRNA, establishing the ring topology and functional redundancy in U6 biogenesis.\",\n      \"evidence\": \"Allele-specific suppressor analysis and snRNP level quantification in yeast\",\n      \"pmids\": [\"11333229\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Lsm2-Lsm8 interaction is direct or mediated through Lsm4 not distinguished biochemically\", \"Mechanism of La/Lsm redundancy not defined\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Demonstration that LSm1-7 (but not LSm8) colocalizes with decapping enzymes in cytoplasmic P-bodies, while LSm2-8 is nuclear, resolved the long-standing question of how shared LSm2-7 subunits partition between two functionally distinct complexes.\",\n      \"evidence\": \"Immunofluorescence, FRET, and dominant-negative mutagenesis in human cells\",\n      \"pmids\": [\"12515382\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism controlling competitive assembly of Lsm1-7 vs Lsm2-8 not yet identified\", \"Whether P-body localization is required for decapping function unclear\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Two parallel discoveries expanded LSm2 functions: the nuclear Lsm2-8 complex was shown to target nuclear-restricted mRNAs for decapping and 5′ degradation, and an Lsm2-7 sub-complex was found to associate with box H/ACA snoRNAs in nucleoli, indicating roles beyond U6 snRNA.\",\n      \"evidence\": \"UV crosslinking and RNA stability assays in yeast export mutants; in vitro reconstitution and sequential IP for snoRNP association\",\n      \"pmids\": [\"15485930\", \"15075370\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Substrates and specificity determinants for nuclear mRNA decapping by Lsm2-8 not defined\", \"Functional consequence of Lsm2-7 association with snoRNAs not established\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Systematic deletion and localization studies established that the intact Lsm2-8 ring is required for nuclear retention of U6 snRNA, and that Lsm1 and Lsm8 compete for shared Lsm2-7 subunits, with stress shifting the equilibrium toward cytoplasmic Lsm1-7 assembly.\",\n      \"evidence\": \"In situ hybridization of U6 in yeast lsm deletion strains; overexpression/depletion with fluorescence imaging\",\n      \"pmids\": [\"17251193\", \"18029398\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signal or modification that triggers stress-dependent redistribution not identified\", \"Whether U6 mislocalization upon Lsm loss is due to export or degradation not fully resolved\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"The crystal structure of the LSm5-6-7 sub-complex revealed a canonical Sm-fold hexameric ring that serves as an assembly intermediate, with NMR confirming LSm2-3 incorporation to form the full ring, resolving the assembly pathway.\",\n      \"evidence\": \"X-ray crystallography at 2.5 Å, NMR spectroscopy, pull-down assays\",\n      \"pmids\": [\"22001694\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full heptameric ring structure with RNA not yet available at this point\", \"Kinetic control of assembly intermediate progression not addressed\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"A crystal structure of the Lsm2-3–Pat1C complex showed that Lsm2 and Lsm3 bridge Pat1 to the Lsm1-7 ring, and this sub-complex is sufficient to stimulate mRNA decapping, answering how the decapping activator is recruited.\",\n      \"evidence\": \"Crystal structure, in vitro decapping assay, structure-based mutagenesis validated in vivo in yeast\",\n      \"pmids\": [\"24247251\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Pat1-Lsm2/3 interaction is regulated or constitutive unknown\", \"Structural basis for full Lsm1-7-Pat1 heptameric complex not resolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Discovery that Pat1b forms a nuclear complex with Lsm2-8 bound to U6 snRNA and SART3 in Cajal bodies extended the Pat1–LSm paradigm to nuclear splicing regulation in human cells, linking Pat1b depletion to alternative splicing defects.\",\n      \"evidence\": \"Co-immunoprecipitation, immunofluorescence, RNAi, and RNA-seq in human cells\",\n      \"pmids\": [\"28768202\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism by which Pat1b-Lsm2-8 influences splice site selection not defined\", \"Whether Pat1b competes with Prp24 for Lsm2-8 binding unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Structure-guided mutagenesis identified Lsm2-R63 as a critical U6-contacting residue, and demonstrated that U6 snRNA overexpression rescues lethality of all Lsm2-8 subunit deletions, proving that the sole essential function of the Lsm2-8 ring in yeast is U6 snRNA support.\",\n      \"evidence\": \"Alanine scanning across 235 pairwise combinations, high-copy suppressor analysis in yeast\",\n      \"pmids\": [\"29615482\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether U6 support is the sole essential function in metazoans not tested\", \"Contribution of non-essential Lsm2-8 functions (nuclear decapping, snoRNA association) to fitness unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Three key advances: cryo-EM structures revealed that 2′,3′-cyclic phosphate recognition discriminates Lsm2-8 from Lsm1-7 RNA selectivity; the Lsm2-8 complex was shown to silence H3K27me3-marked heterochromatic genes via XRN-2; and prefoldins were identified as Hsp90-dependent chaperones for Lsm2-8 assembly in plants.\",\n      \"evidence\": \"Four high-resolution cryo-EM structures with RNA-binding assays; genetic epistasis with xrn-2 and ChIP in C. elegans; co-IP and Hsp90 inhibitor studies in Arabidopsis\",\n      \"pmids\": [\"32518066\", \"32251399\", \"32396196\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether cyclic phosphate recognition by Lsm2-8 is conserved in metazoans at structural level not confirmed\", \"How Lsm2-8 is recruited specifically to H3K27me3-target transcripts unknown\", \"Whether the PFD-Hsp90 axis for Lsm2-8 assembly operates in animals not tested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Single-molecule kinetics revealed that 3′-end processing of U6 and Prp24 cooperatively control Lsm2-8 assembly, and a mouse conditional knockout demonstrated that Lsm2 is essential for Club cell maintenance and lung epithelial homeostasis.\",\n      \"evidence\": \"CoSMoS with reconstituted components and defined RNA modifications; Club cell-specific Lsm2 knockout in mice with snRNA-seq and immunohistochemistry\",\n      \"pmids\": [\"40216252\", \"40022153\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Prp24-dependent kinetic selection operates in human cells not shown\", \"Mechanistic link between Lsm2 RNA processing functions and Club cell survival not defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major open questions include the structural basis of full Lsm1-7-Pat1 and Lsm2-8-Pat1b holo-complexes, how Lsm2-8 is recruited to heterochromatic transcripts, whether the sole-essential-function paradigm for U6 support extends to metazoan systems, and the molecular mechanism linking Lsm2 loss to epithelial cell fate decisions.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No full heptameric Lsm1-7-Pat1 or Lsm2-8-Pat1b complex structure\", \"Mechanism of Lsm2-8 targeting to H3K27me3-marked transcripts unknown\", \"Essential function of Lsm2-8 in metazoans not genetically delineated as in yeast\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [0, 3, 4, 10, 11, 14]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 7, 8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [2, 3, 5, 6, 9]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [2, 8]},\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [0, 1, 3, 4, 5, 8, 10, 11, 12, 14]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [9, 13]}\n    ],\n    \"complexes\": [\n      \"LSm2-8 heptameric ring\",\n      \"LSm1-7 heptameric ring\",\n      \"LSm2-3-Pat1C complex\",\n      \"U4/U6.U5 tri-snRNP\"\n    ],\n    \"partners\": [\n      \"LSM8\",\n      \"LSM3\",\n      \"LSM4\",\n      \"PAT1B\",\n      \"SART3\",\n      \"PRP24\",\n      \"LSM1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}