Affinage

SNRPD1

Small nuclear ribonucleoprotein Sm D1 · UniProt P62314

Round 2 corrected
Length
119 aa
Mass
13.3 kDa
Annotated
2026-04-28
38 papers in source corpus 12 papers cited in narrative 12 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

SNRPD1 (SmD1) is a core Sm protein of the spliceosomal snRNP machinery, forming a heterodimeric complex with SmD2 via a conserved Sm fold and assembling into the heptameric Sm ring that encircles U1, U2, U4, and U5 snRNAs, while being specifically excluded from U7 snRNPs where Lsm10 substitutes (PMID:10025403, PMID:11574479, PMID:12226669). Its C-terminal arginine-glycine-rich domain undergoes symmetric dimethylation by the PRMT5/pICln-containing methylosome; pICln binding prevents premature Sm core assembly, and subsequent sDMA modification redirects SmD1 to the SMN complex for regulated snRNP biogenesis (PMID:11713266, PMID:11747828). SMN directly binds SmD1 and other Sm proteins, coupling snRNP assembly to the survival of motor neurons pathway (PMID:9323129). In cancer cells, SNRPD1 depletion arrests the cell cycle at G0/G1, activates autophagy, and suppresses the PI3K/AKT/mTOR/4EBP1 axis, with SNRPD1 mRNA stability maintained by IGF2BP2-mediated m6A recognition (PMID:37268273, PMID:39411513).

Mechanistic history

Synthesis pass · year-by-year structured walk · 11 steps
  1. 1997 High

    Establishing that SNRPD1 is a direct physical partner of the SMN complex resolved how Sm proteins are chaperoned during snRNP biogenesis and linked spliceosome assembly to the spinal muscular atrophy gene product.

    Evidence Co-immunoprecipitation and direct binding assays between SMN/SIP1 and Sm proteins including SmD1

    PMID:9323129

    Open questions at the time
    • Stoichiometry of SMN–SmD1 interaction not defined
    • Whether SMN binding requires prior methylation of SmD1 was unknown
  2. 1997 Medium

    Characterization of the SNRPD1 gene structure and promoter identified coordinate regulatory motifs shared with other snRNP component genes, establishing a basis for transcriptional co-regulation.

    Evidence Southern blotting, sequencing, and CAT reporter assay of SNRPD1 promoter

    PMID:9168134

    Open questions at the time
    • Trans-acting factors driving the shared promoter motifs were not identified
    • In vivo transcriptional regulation not tested
  3. 1999 High

    The crystal structure of the SmD1–SmD2 heterodimer revealed the conserved Sm fold and showed how pairwise Sm interactions generate a heptameric ring with a positively charged central channel for snRNA threading, providing the first atomic-resolution model of Sm ring architecture.

    Evidence X-ray crystallography of the D1–D2 dimer

    PMID:10025403

    Open questions at the time
    • Full heptameric ring structure with RNA not yet resolved at that time
    • Structural basis of RNA sequence selectivity by the Sm ring was unresolved
  4. 2001 High

    Discovery that PRMT5/pICln symmetrically dimethylates SmD1's RG domain and that pICln binding blocks premature Sm core assembly while sDMA modification redirects SmD1 to SMN revealed a two-step quality-control checkpoint in snRNP biogenesis.

    Evidence In vitro methyltransferase assays, Sm core assembly reconstitution, and co-immunoprecipitation

    PMID:11713266 PMID:11747828

    Open questions at the time
    • Individual arginine residues required for sDMA-dependent SMN binding not mapped
    • Kinetic parameters of the methylation-assembly switch not determined
  5. 2001 High

    Demonstrating that U7 snRNPs lack SmD1 and SmD2 — replaced by Lsm10 — and that this exclusion is dictated by the U7 Sm site sequence established that Sm ring composition is RNA-specified, not protein-intrinsic.

    Evidence Affinity purification of U7 snRNPs, microsequencing, immunofluorescence

    PMID:11574479

    Open questions at the time
    • Structural basis for Sm site discrimination between canonical and U7 snRNA not resolved
    • Whether other Sm-like substitutions exist in specialized snRNPs was unknown
  6. 2002 High

    Mass-spectrometric identification of SmD1 as a component of the purified functional spliceosome confirmed its presence in the catalytically active splicing machinery beyond snRNP particles.

    Evidence Affinity-purified spliceosome analyzed by LC-MS/MS

    PMID:12226669

    Open questions at the time
    • Whether SmD1 has a function in the spliceosome beyond structural scaffolding was not addressed
  7. 2003 Medium

    The finding that HCV NS3 directly binds SmD1's GR-repeat domain and redistributes to the nucleus suggested a viral strategy for co-opting the snRNP assembly pathway.

    Evidence Yeast two-hybrid, deletion mutagenesis, and immunostaining in co-transfected cells

    PMID:14524621

    Open questions at the time
    • Functional consequence on splicing or viral replication not tested
    • Interaction not confirmed by reciprocal co-IP from infected cells
    • Whether NS3–SmD1 binding competes with sDMA-dependent SMN recognition is unknown
  8. 2017 Medium

    Showing that SNRPD1 is upregulated during iPSC reprogramming and required for pluripotency acquisition linked spliceosome activity to cell fate transitions and identified SmD1 as rate-limiting for spliceosome assembly in stem cells.

    Evidence siRNA knockdown in reprogramming assays, co-IP with SNRPA1 and PNN, co-localization with spliceosomal markers

    PMID:28595116

    Open questions at the time
    • Specific splicing events affected by SmD1 depletion in stem cells not catalogued
    • Whether other Sm proteins are similarly limiting for pluripotency was not tested
  9. 2021 Medium

    SNRPD1 knockdown-induced G0/G1 arrest and altered doxorubicin sensitivity in breast cancer cells revealed a non-canonical role for SmD1 in cell cycle progression and drug response that varies by cancer subtype.

    Evidence siRNA knockdown, flow cytometry, drug sensitivity assays in TNBC and luminal breast cancer lines

    PMID:33879154

    Open questions at the time
    • Whether the cell cycle effect is splicing-dependent or due to a moonlighting function was not determined
    • Specific downstream splicing targets mediating the phenotype are unknown
  10. 2023 Medium

    Demonstration that SmD1 depletion in hepatocellular carcinoma activates autophagy and suppresses the PI3K/AKT/mTOR/4EBP1 axis in vitro and in xenografts identified a signaling pathway through which SNRPD1 sustains proliferative signaling in cancer.

    Evidence siRNA knockdown, western blotting for pathway components, autophagy assays, in vivo xenograft tumor growth

    PMID:37268273

    Open questions at the time
    • Whether PI3K/AKT suppression is a direct effect or secondary to global splicing disruption is unresolved
    • No rescue experiment with catalytically active PI3K was performed
  11. 2024 Medium

    Identification of IGF2BP2 as an m6A-dependent stabilizer of SNRPD1 mRNA provided the first post-transcriptional regulatory mechanism controlling SmD1 protein levels in cancer, connecting epitranscriptomic regulation to the spliceosomal core.

    Evidence RIP, MeRIP, RNA stability assays, functional rescue by IGF2BP2 overexpression in TNBC cells

    PMID:39411513

    Open questions at the time
    • Specific m6A sites on SNRPD1 mRNA not mapped
    • Whether this regulatory axis operates in non-malignant contexts is unknown
    • Single-lab finding without independent replication

Open questions

Synthesis pass · forward-looking unresolved questions
  • It remains unresolved whether the oncogenic effects of SNRPD1 overexpression reflect global splicing dysfunction, specific mis-splicing of cancer-relevant transcripts, or splicing-independent moonlighting functions of SmD1.
  • No transcriptome-wide splicing analysis after SNRPD1 perturbation in cancer models
  • Structural basis of how sDMA modification modulates the SmD1–SMN interface at atomic resolution is lacking
  • Whether SmD1 has direct signaling roles outside its spliceosomal function has not been tested with separation-of-function mutants

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0003723 RNA binding 3 GO:0005198 structural molecule activity 2
Localization
GO:0005634 nucleus 2 GO:0005654 nucleoplasm 2
Pathway
R-HSA-8953854 Metabolism of RNA 5 R-HSA-392499 Metabolism of proteins 2
Partners
CLNS1AIGF2BP2PNNPRMT5SMN1SNRPA1SNRPD2
Complex memberships
PRMT5/pICln methylosomeSMN complexSm heptameric ring (SmB/B', SmD1, SmD2, SmD3, SmE, SmF, SmG)Spliceosome

Evidence

Reading pass · 12 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1999 Crystal structure of the SmD1-SmD2 heterodimer revealed that Sm proteins share a common fold consisting of an N-terminal helix followed by a strongly bent five-stranded antiparallel beta sheet, and that the D1D2 dimer interface closely superposes with the D3B dimer, suggesting the seven Sm proteins form a closed ring through which snRNA is threaded in a positively charged central hole. X-ray crystallography Cell High 10025403
1997 SMN (Survival of Motor Neurons protein) directly interacts with spliceosomal snRNP Sm core proteins including SmD1 (SNRPD1), SmD2, SmD3, SmB, and SmE, forming a specific complex with the SIP1-associated SMN protein, implicating SMN and SIP1 in snRNP biogenesis. Co-immunoprecipitation, direct binding assays Cell High 9323129
2001 SNRPD1's C-terminal arginine- and glycine-rich (RG) domain is symmetrically dimethylated on arginine residues (sDMA) by the 20S methylosome complex containing the methyltransferase JBP1 and pICln; unmodified SmD1 RG domain binds JBP1 and pICln, while sDMA-modified SmD1 binds preferentially to SMN, directing Sm proteins to the SMN complex for snRNP assembly. In vitro methyltransferase assay, co-immunoprecipitation, biochemical fractionation Molecular and cellular biology High 11713266
2001 SNRPD1 arginine residues in the RG-rich C-terminal domain are modified to symmetrical dimethylarginines (sDMAs) by a pICln-containing complex that includes PRMT5; pICln binding to the Sm fold of SmD1 inhibits spontaneous Sm core assembly onto U snRNA by preventing Sm–Sm interactions required for Sm core formation, suggesting the pICln complex regulates an early step in U snRNP assembly. In vitro methylation assay, co-immunoprecipitation, Sm core assembly assay Current biology : CB High 11747828
2001 Purified U7 snRNPs lack the canonical Sm proteins D1 (SNRPD1) and D2, and instead contain a novel Sm-like protein (Lsm10) related to SmD1/D3; this absence of SNRPD1 from U7 snRNPs is largely dictated by the special Sm-binding site of U7 snRNA, demonstrating that the identity of the Sm site determines which Sm proteins are incorporated. Biochemical fractionation, affinity purification with biotinylated oligonucleotide, microsequencing, immunofluorescence The EMBO journal High 11574479
2002 SNRPD1 was identified as a component of the purified, functional human spliceosome by mass spectrometry, confirming its presence in the ~145-protein spliceosomal machinery. Affinity purification mass spectrometry (MBP-affinity chromatography + LC-MS/MS) Nature High 12226669
2003 HCV nonstructural protein NS3 directly binds SNRPD1 via the C-terminal GR-repeat region of SmD1; co-expression of NS3 altered SmD1 expression levels and caused NS3 to redistribute to the nucleus, demonstrating that the SmD1–NS3 interaction can alter subcellular localization of NS3. Yeast two-hybrid, deletion mutagenesis, immunostaining Microbiology and immunology Medium 14524621
1997 The human SNRPD1 gene was identified as a three-intron-containing functional gene within a multigene family; two other family members are processed pseudogenes. A 0.38 kb promoter region was shown to drive transcription by CAT reporter assay, and the promoter shares homologous sequence motifs with the SmE gene and U1 snRNA gene promoters, suggesting coordinate regulation of snRNP component genes. Southern blotting, DNA sequencing, CAT reporter gene fusion assay Gene Medium 9168134
2017 SNRPD1 is significantly upregulated during early reprogramming of human somatic cells to iPSCs; depletion of SNRPD1 caused pronounced loss of pluripotency and blocked hiPS generation; SNRPD1 co-localizes with spliceosomal components in hPS cells, physically interacts with SNRPA1 and PNN, and positively influences hPS spliceosome assembly. siRNA knockdown, co-immunoprecipitation, co-localization immunofluorescence, reprogramming assay Stem cell research Medium 28595116
2021 Knockdown of SNRPD1 in breast cancer cells arrested the cell cycle at G0/G1 phase and halted tumor cell growth; reduced SNRPD1 expression also decreased sensitivity of triple-negative breast cancer cells to doxorubicin, while luminal cancer cells were unaffected. siRNA knockdown, flow cytometry cell cycle analysis, western blotting, qPCR, drug response assay Cancer cell international Medium 33879154
2023 SNRPD1 knockdown in hepatocellular carcinoma cells suppressed proliferation, migration, and invasion, induced G0/G1 cell cycle arrest and apoptosis, increased autophagic vacuoles and expression of autophagy genes (ATG5, ATG7, ATG12), and blocked the PI3K/AKT/mTOR/4EBP1 signaling pathway; SNRPD1 inhibition also suppressed tumor growth in vivo. siRNA knockdown, western blotting, flow cytometry, autophagy assays, in vivo xenograft Archives of biochemistry and biophysics Medium 37268273
2024 IGF2BP2, an m6A reader, binds SNRPD1 mRNA and enhances its stability via m6A-dependent mechanisms, thereby increasing SNRPD1 protein levels in triple-negative breast cancer cells; IGF2BP2 overexpression reversed the anti-tumor effects of SNRPD1 knockdown. RIP assay, methylated RNA immunoprecipitation (MeRIP), qRT-PCR for RNA stability, siRNA knockdown, Western blot Breast cancer (Dove Medical Press) Medium 39411513

Source papers

Stage 0 corpus · 38 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2012 Insights into RNA biology from an atlas of mammalian mRNA-binding proteins. Cell 1718 22658674
2002 Generation and initial analysis of more than 15,000 full-length human and mouse cDNA sequences. Proceedings of the National Academy of Sciences of the United States of America 1479 12477932
2015 The BioPlex Network: A Systematic Exploration of the Human Interactome. Cell 1118 26186194
2017 Architecture of the human interactome defines protein communities and disease networks. Nature 1085 28514442
2015 A human interactome in three quantitative dimensions organized by stoichiometries and abundances. Cell 1015 26496610
2014 A proteome-scale map of the human interactome network. Cell 977 25416956
2012 The mRNA-bound proteome and its global occupancy profile on protein-coding transcripts. Molecular cell 973 22681889
2020 A reference map of the human binary protein interactome. Nature 849 32296183
2018 VIRMA mediates preferential m6A mRNA methylation in 3'UTR and near stop codon and associates with alternative polyadenylation. Cell discovery 829 29507755
2002 Comprehensive proteomic analysis of the human spliceosome. Nature 725 12226669
2021 Dual proteome-scale networks reveal cell-specific remodeling of the human interactome. Cell 705 33961781
2012 A census of human soluble protein complexes. Cell 689 22939629
2011 Phylogenetic-based propagation of functional annotations within the Gene Ontology consortium. Briefings in bioinformatics 656 21873635
2018 High-Density Proximity Mapping Reveals the Subcellular Organization of mRNA-Associated Granules and Bodies. Molecular cell 580 29395067
1997 The spinal muscular atrophy disease gene product, SMN, and its associated protein SIP1 are in a complex with spliceosomal snRNP proteins. Cell 569 9323129
2017 Anticancer sulfonamides target splicing by inducing RBM39 degradation via recruitment to DCAF15. Science (New York, N.Y.) 533 28302793
2004 The status, quality, and expansion of the NIH full-length cDNA project: the Mammalian Gene Collection (MGC). Genome research 438 15489334
2022 OpenCell: Endogenous tagging for the cartography of human cellular organization. Science (New York, N.Y.) 432 35271311
2010 Systematic analysis of human protein complexes identifies chromosome segregation proteins. Science (New York, N.Y.) 421 20360068
2013 The intracellular interactome of tetraspanin-enriched microdomains reveals their function as sorting machineries toward exosomes. The Journal of biological chemistry 413 23463506
2015 Panorama of ancient metazoan macromolecular complexes. Nature 407 26344197
2011 IFIT1 is an antiviral protein that recognizes 5'-triphosphate RNA. Nature immunology 405 21642987
2011 Image-based genome-wide siRNA screen identifies selective autophagy factors. Nature 405 22020285
1999 Crystal structures of two Sm protein complexes and their implications for the assembly of the spliceosomal snRNPs. Cell 374 10025403
2007 Functional specialization of beta-arrestin interactions revealed by proteomic analysis. Proceedings of the National Academy of Sciences of the United States of America 360 17620599
2005 The response of autologous T cells to a human melanoma is dominated by mutated neoantigens. Proceedings of the National Academy of Sciences of the United States of America 357 16247014
2001 The methylosome, a 20S complex containing JBP1 and pICln, produces dimethylarginine-modified Sm proteins. Molecular and cellular biology 354 11713266
2021 A proximity-dependent biotinylation map of a human cell. Nature 339 34079125
2003 Splicing double: insights from the second spliceosome. Nature reviews. Molecular cell biology 329 14685174
2001 Methylation of Sm proteins by a complex containing PRMT5 and the putative U snRNP assembly factor pICln. Current biology : CB 323 11747828
2001 Purified U7 snRNPs lack the Sm proteins D1 and D2 but contain Lsm10, a new 14 kDa Sm D1-like protein. The EMBO journal 138 11574479
2017 The unique spliceosome signature of human pluripotent stem cells is mediated by SNRPA1, SNRPD1, and PNN. Stem cell research 26 28595116
2021 SNRPD1 confers diagnostic and therapeutic values on breast cancers through cell cycle regulation. Cancer cell international 19 33879154
1997 Screening of SLE sera using purified recombinant Sm-D1 protein from a baculovirus expression system. Clinical immunology and immunopathology 17 9175921
2023 SNRPD1 inhibition suppresses the proliferation of hepatocellular carcinoma and promotes autophagy through the PI3K/AKT/mTOR/4EBP1 pathway. Archives of biochemistry and biophysics 10 37268273
2003 Hepatitis C virus nonstructural protein NS3 binds to Sm-D1, a small nuclear ribonucleoprotein associated with autoimmune disease. Microbiology and immunology 10 14524621
2024 The Potential Role of SNRPD1 Stabilized by IGF2BP2 in the Progression of Triple-Negative Breast Cancer. Breast cancer (Dove Medical Press) 1 39411513
1997 Analysis of genes for human snRNP Sm-D1 protein and identification of the promoter sequence which shows segmental homology to the promoters of Sm-E and U1 snRNA genes. Gene 1 9168134