Affinage

LSM3

U6 snRNA-associated Sm-like protein LSm3 · UniProt P62310

Length
102 aa
Mass
11.8 kDa
Annotated
2026-06-10
22 papers in source corpus 10 papers cited in narrative 10 extracted findings
Cross-family judge vs UniProt: tie faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

LSM3 is a conserved Sm-like protein that functions as a shared subunit of two heptameric Lsm rings linking RNA splicing to mRNA decay (PMID:24240276, PMID:24139796). In the nuclear Lsm2-8 ring, which adopts a doughnut-shaped assembly with subunit order Lsm3-2-8-4-7-5-6, Lsm3 occupies a critical RNA-contacting position: its His36 and Arg69 sandwich the 3'-terminal uracil of U6 snRNA via π-π and cation-π interactions (PMID:24240276). This contact is the basis of the complex's sole essential function — structure-guided alanine scanning identified Lsm3-R69A as the only lethal mutation among 39 tested positions, and the lethality of LSM3 deletion is rescued by overexpression of U6 snRNA or the U6 snRNP subunit Prp24, establishing that the Lsm2-8 ring exists in vivo to stabilize and recruit U6 snRNA for pre-mRNA splicing (PMID:29615482). In the cytoplasmic Lsm1-7 ring, Lsm3 together with Lsm2 forms the docking surface for the C-terminal domain of the decapping activator Pat1; a reconstituted Lsm2-3–Pat1C subcomplex stimulates mRNA decapping in vitro comparably to the full Lsm1-7–Pat1C complex, coupling deadenylation to decapping (PMID:24139796, PMID:24247251). Consistent with this decay role, LSm3 is recruited to P-bodies in a manner dependent on the CCR4-NOT deadenylase and coincident with maternal mRNA degradation (PMID:18692039), and is required for development, reproduction, and insulin/IGF-1-regulated stress responses (PMID:26150554). LSM3 additionally co-occupies chromatin with Mediator at intron-containing ribosomal protein genes to control their growth-regulated transcription and splicing (PMID:38613396), and its knockdown lengthens the circadian period through effects on clock-gene RNA processing (PMID:25288739).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 2008 Medium

    Before its ring context was resolved, it was unclear how Lsm3 itself oligomerizes and selects partners; the first Lsm3 structure showed it can self-assemble and recruit specific Lsm subunits, hinting at its assembly role.

    Evidence X-ray crystallography of yeast Lsm3 plus pull-down from yeast lysate

    PMID:18329667

    Open questions at the time
    • The octameric homomeric ring is a crystallization artifact relative to the physiological heptamer
    • Recruitment shown only from crude lysate, not reconstituted
    • Does not address RNA recognition
  2. 2008 Medium

    It was unknown whether Lsm3 participates in cytoplasmic mRNA turnover in vivo; imaging in C. elegans embryos placed LSM-3 in P-bodies downstream of deadenylation.

    Evidence Live fluorescence imaging and CCR4-NOT (LET-711) depletion in embryos

    PMID:18692039

    Open questions at the time
    • Recruitment is correlative with deadenylation, not mechanistically dissected
    • Cell-type specificity (soma vs germline) basis unexplained
  3. 2012 High

    Whether Lsm3 binds RNA alone or only in a complex was unresolved; this work showed the Lsm2/3 heterodimer, not Lsm3 monomer, is the minimal RNA-binding unit.

    Evidence X-ray crystallography, analytical ultracentrifugation, and oligo(U) RNA-binding assays in S. pombe

    PMID:22615807

    Open questions at the time
    • Does not establish base-specific recognition residues
    • In-crystal heptamer of Lsm3 differs from physiological assembly
  4. 2013 High

    How the Lsm2-8 ring recognizes U6 snRNA was unknown; the atomic structure defined subunit order and the Lsm3 His36/Arg69 sandwich of the 3'-terminal uracil.

    Evidence 2.8 Å crystal structure of Lsm2-8 bound to U6 3' end with biochemical assays

    PMID:24240276

    Open questions at the time
    • Static structure does not address assembly kinetics
    • Does not test which contacts are essential in vivo
  5. 2013 High

    The basis for Pat1-dependent coupling of decay to the cytoplasmic ring was unclear; structures showed Lsm2 and Lsm3 — not the cytoplasm-specific Lsm1 — provide the Pat1 docking surface, and the minimal Lsm2-3–Pat1C unit activates decapping.

    Evidence Crystal structures of Lsm1-7, Lsm1-7–Pat1C, and Lsm2-3–Pat1C with in vitro decapping and RNA-binding assays plus in vivo mutagenesis

    PMID:24139796 PMID:24247251

    Open questions at the time
    • Stoichiometry of Pat1 binding in the full cellular ring not defined
    • Does not connect decapping activation to specific transcript classes
  6. 2015 Medium

    The organismal consequences of losing lsm-3 were uncharacterized; loss-of-function linked it to development, reproduction, stress granule formation, and insulin/IGF-1 signaling outputs.

    Evidence RNAi and loss-of-function mutants with DAF-16::GFP reporter and stress phenotype assays in C. elegans

    PMID:26150554

    Open questions at the time
    • Phenotypes do not isolate splicing vs decay contributions
    • Direct molecular targets in the IIS pathway not identified
  7. 2018 High

    Which Lsm2-8 contact is functionally indispensable, and what the ring's essential role is, were open; mutagenesis pinpointed Lsm3-R69 and genetic rescue established U6 support as the sole essential function.

    Evidence Alanine scanning across 39 residues plus deletion rescue by U6 or Prp24 overexpression in S. cerevisiae

    PMID:29615482

    Open questions at the time
    • Does not address non-essential Lsm3 functions in decay or transcription
    • Rescue assays measure viability, not splicing fidelity directly
  8. 2024 Medium

    A chromatin-associated role for Lsm3 was unknown; ChIP-seq revealed it co-occupies ribosomal protein genes with Mediator to control growth-regulated transcription and splicing.

    Evidence ChIP-seq (Lsm3, Med1, Med15) with RNA-seq correlation in S. cerevisiae

    PMID:38613396

    Open questions at the time
    • Mechanism is correlative; no mutagenesis of the Lsm3-Mediator interface
    • Whether chromatin recruitment requires the Lsm2-8 ring is untested
  9. 2014 Medium

    Whether Lsm3-dependent RNA processing feeds into physiological rhythms was unknown; knockdown lengthened the circadian period via clock-gene splicing.

    Evidence siRNA knockdown and circadian period measurement in human cells

    PMID:25288739

    Open questions at the time
    • Specific clock-gene splicing events not mapped
    • Cannot separate Lsm2-8 vs Lsm1-7 contribution

Open questions

Synthesis pass · forward-looking unresolved questions
  • How the same Lsm3 subunit is partitioned between nuclear splicing, cytoplasmic decay, and chromatin/Mediator functions, and whether these reflect distinct ring contexts, remains unresolved.
  • No assay distinguishes which ring drives the chromatin and circadian phenotypes
  • Regulation of Lsm3 sorting between rings unknown

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0003723 RNA binding 2 GO:0005198 structural molecule activity 2 GO:0098772 molecular function regulator activity 1
Localization
GO:0005634 nucleus 2 GO:0005829 cytosol 2
Pathway
R-HSA-8953854 Metabolism of RNA 3
Complex memberships
Lsm1-7 complexLsm2-8 complexP-body

Evidence

Reading pass · 10 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2013 Crystal structure of the heptameric Lsm2-8 complex (including Lsm3) bound to the 3' end of U6 snRNA at 2.8 Å resolution revealed the subunit order Lsm3-2-8-4-7-5-6 in a doughnut-shaped assembly. The four 3'-terminal uridines of U6 snRNA are modularly recognized by Lsm3, Lsm2, Lsm8, and Lsm4; uracil base specificity is conferred by a conserved asparagine residue. The 3'-terminal uracil is sandwiched by His36 and Arg69 of Lsm3 via π-π and cation-π interactions, respectively. X-ray crystallography at 2.8 Å with associated biochemical assays Nature High 24240276
2013 Crystal structure of S. cerevisiae Lsm1-7 at 2.3 Å resolution showed a heptameric ring with subunit order Lsm1-2-3-6-5-7-4. Pat1 recognition by the Lsm1-7 complex is mediated by Lsm2 and Lsm3 (not by the cytoplasm-specific Lsm1 subunit), as revealed by the 3.7 Å structure of Lsm1-7 bound to the C-terminal domain of Pat1. X-ray crystallography at 2.3 Å (Lsm1-7) and 3.7 Å (Lsm1-7–Pat1C complex) Cell reports High 24139796
2013 Lsm2 and Lsm3 directly bridge the interaction between the Lsm1-7 heptamer and the C-terminus of Pat1 (Pat1C). The crystal structure of the Lsm2-3–Pat1C complex shows three Pat1C molecules surrounding a heptameric ring of Lsm2-3. The Lsm2-3–Pat1C complex and Lsm1-7–Pat1C complex both stimulate mRNA decapping in vitro to a similar extent and exhibit similar RNA-binding preference. Structure-based mutagenesis confirmed the importance of these contacts for decapping activation in vivo. X-ray crystallography, in vitro decapping assay, RNA-binding assay, structure-guided mutagenesis, in vivo functional assay Cell research High 24247251
2008 Crystal structure of yeast Lsm3 reveals a novel octameric (8-subunit) ring organization of the Sm-fold, distinct from the canonical heptameric arrangement. The homomeric Lsm3 octamer can directly recruit Lsm6, Lsm2, and Lsm5 from yeast lysate, and the C-terminal tail of Lsm3 engages in inter-ring β-sheet interactions via specific protein–protein contacts. X-ray crystallography; pull-down from yeast lysate Journal of molecular biology Medium 18329667
2012 Crystal structure of S. pombe Lsm3 shows it forms a heptamer within the crystal lattice and in solution (confirmed by analytical ultracentrifugation). RNA-binding assays demonstrated that Lsm2/3 together bind oligo(U) RNA, whereas Lsm3 alone does not bind oligo(U), indicating that the complete Lsm2/3 heterodimer is required for RNA binding. X-ray crystallography, analytical ultracentrifugation, RNA-binding assay PloS one High 22615807
2018 Structure-guided alanine scanning of S. cerevisiae Lsm2-8 residues at RNA-binding sites and intersubunit interfaces identified Lsm3-R69A as the sole lethal mutation among 39 positions tested, consistent with Arg69 of Lsm3 being essential for binding the 3'-terminal UUU of U6 snRNA. Deletion of LSM3 (lsm3Δ) is lethal but is rescued by overexpression of U6 snRNA or U6 snRNP subunit Prp24, indicating that the only essential function of the Lsm2-8 ring is to support U6 snRNA. Systematic alanine-scanning mutagenesis; yeast genetics (deletion rescue by U6 overexpression or Prp24 overexpression); growth assays RNA (New York, N.Y.) High 29615482
2008 In C. elegans embryos, LSM-3 (along with LSM-1) is recruited to P-bodies specifically in somatic blastomeres, not germline blastomeres. This recruitment requires the LET-711/Not1 subunit of the CCR4-NOT deadenylase complex and correlates spatially and temporally with the onset of maternal mRNA degradation. Live fluorescence imaging; genetic requirement tested by depleting CCR4-NOT subunit LET-711 Developmental biology Medium 18692039
2015 In C. elegans, lsm-3 (along with lsm-1) is required for normal development, reproduction, and motility. Under stress conditions, cytoplasmic LSm proteins aggregate into granules in an LSM-1-dependent manner, and lsm-3 is required for processes regulated by the insulin/IGF-1 signaling (IIS) pathway including aging and pathogen resistance. RNAi knockdown, loss-of-function mutations, DAF-16::GFP reporter assays, stress phenotype assays RNA (New York, N.Y.) Medium 26150554
2024 ChIP-seq in S. cerevisiae revealed that Lsm3 co-occupies chromatin with Mediator subunits Med1/Med15 at 86 genes, of which 73 are intron-containing ribosomal protein genes. During late exponential growth, Mediator transitions from gene promoters to 3'-exon positions overlapping Lsm3 binding sites ~250 bp downstream of the last intron-exon boundary. This transition correlates with reduced mRNA levels and reduced splicing ratios for these genes, indicating that Lsm3 and Mediator cooperate to control growth-regulated transcription and splicing of ribosomal protein genes. ChIP-seq (Lsm3, Med1, Med15); RNA-seq; correlation of chromatin occupancy with mRNA levels and splicing ratios Nucleic acids research Medium 38613396
2014 Knockdown of LSM3 (as well as LSM5 or LSM7) in human cells lengthens the circadian period, placing LSM3 as a regulator of circadian rhythm via its role in RNA processing (alternative splicing) of core clock genes. siRNA knockdown in human cells; circadian period measurement Proceedings of the National Academy of Sciences of the United States of America Medium 25288739

Source papers

Stage 0 corpus · 22 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2008 Processing bodies and germ granules are distinct RNA granules that interact in C. elegans embryos. Developmental biology 121 18692039
2013 Crystal structures of the Lsm complex bound to the 3' end sequence of U6 small nuclear RNA. Nature 86 24240276
2020 The Predicted Key Molecules, Functions, and Pathways That Bridge Mild Cognitive Impairment (MCI) and Alzheimer's Disease (AD). Frontiers in neurology 66 32308643
2013 Architecture of the Lsm1-7-Pat1 complex: a conserved assembly in eukaryotic mRNA turnover. Cell reports 65 24139796
2014 Role for LSM genes in the regulation of circadian rhythms. Proceedings of the National Academy of Sciences of the United States of America 56 25288739
2010 Analysis of spliceosomal proteins in Trypanosomatids reveals novel functions in mRNA processing. The Journal of biological chemistry 38 20592024
2013 Lsm2 and Lsm3 bridge the interaction of the Lsm1-7 complex with Pat1 for decapping activation. Cell research 35 24247251
2008 Crystal structure of Lsm3 octamer from Saccharomyces cerevisiae: implications for Lsm ring organisation and recruitment. Journal of molecular biology 25 18329667
2021 Immune-Omics Networks of CD27, PD1, and PDL1 in Non-Small Cell Lung Cancer. Cancers 17 34503105
2017 Next-generation sequencing reveals lymph node metastasis associated genetic markers in colorectal cancer. Experimental and therapeutic medicine 16 28672935
2015 Cytoplasmic LSM-1 protein regulates stress responses through the insulin/IGF-1 signaling pathway in Caenorhabditis elegans. RNA (New York, N.Y.) 15 26150554
2012 Crystal structures of Lsm3, Lsm4 and Lsm5/6/7 from Schizosaccharomyces pombe. PloS one 15 22615807
2021 Characterization and comparative genomic analysis of gamma-aminobutyric acid (GABA)-producing lactic acid bacteria from Thai fermented foods. Biotechnology letters 12 33999363
2025 Unsupervised Classification of the Host Response Identifies Dominant Pathobiological Signatures of Sepsis in Sub-Saharan Africa. American journal of respiratory and critical care medicine 10 39514831
2021 Mechanical stretching of cells and lipid nanoparticles for nucleic acid delivery. Journal of controlled release : official journal of the Controlled Release Society 9 34563590
2018 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. RNA (New York, N.Y.) 8 29615482
2010 Antigen-subtracted 2-DE/MS strategy, a novel proteomic analysis platform. Archives of toxicology 4 20407759
2025 Continuous Engineering of Phenylalanine Ammonia Lyase from Lettuce (Lactuca sativa L.) for Efficient Synthesis of 3,4-Substituted Phenylalanine. Journal of agricultural and food chemistry 3 40254840
2025 Interfacial properties and stability of Pickering emulsion stabilized by silkworm pupa protein and preparation of emulsion-filled hydrogel with high hardness: Effect of sodium alginate and ultrasonication. International journal of biological macromolecules 3 40446995
2024 Growth-regulated co-occupancy of Mediator and Lsm3 at intronic ribosomal protein genes. Nucleic acids research 2 38613396
2024 Peripheral Blood CD8+ T-Lymphocyte Immune Response in Benign and Subpopulations of Breast Cancer Patients. International journal of molecular sciences 2 38928129
2020 Species and tissue specific analysis based on quantitative proteomics from allotetraploid and the parents. Journal of proteomics 2 33309926

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