Affinage

SNAPC4

snRNA-activating protein complex subunit 4 · UniProt Q5SXM2

Length
1469 aa
Mass
159.4 kDa
Annotated
2026-04-28
31 papers in source corpus 17 papers cited in narrative 17 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

SNAPC4 (SNAP190) is the largest subunit of the five-subunit SNAPc complex and serves as the central scaffold for snRNA gene transcription by both RNA polymerase II and III. Its 4.5-repeat Myb DNA-binding domain directly recognizes the proximal sequence element (PSE) of snRNA promoters in a wrap-around mode together with SNAP50 and SNAP43, while also recruiting TBP to the adjacent TATA box and providing the docking surface for cooperative activation by the Oct-1 POU domain (PMID:9418884, PMID:36369505, PMID:12414730, PMID:12391172). CK2 phosphorylation of the SNAP190 N-terminal region allosterically inhibits its DNA-binding activity, and proper complex assembly depends on SUMOylation of the SNAPC1 subunit to maintain the SNAPC1–SNAPC4 interaction (PMID:17670747, PMID:40956881). Bi-allelic loss-of-function SNAPC4 variants in humans cause reduced snRNA levels, global alternative splicing dysregulation, and a neurodegenerative disorder featuring neuroregression and progressive spastic paraparesis (PMID:36965478).

Mechanistic history

Synthesis pass · year-by-year structured walk · 12 steps
  1. 1998 High

    Identification of SNAP190 as the largest SNAPc subunit and its Myb domain as the direct PSE-binding module resolved how the complex recognizes snRNA promoters, and full reconstitution of SNAPc from five recombinant subunits established SNAP190 as essential for both Pol II and Pol III snRNA transcription.

    Evidence cDNA cloning, recombinant PSE-binding assays, five-subunit reconstitution with in vitro transcription

    PMID:9418884 PMID:9732265

    Open questions at the time
    • Full-length structural model of the Myb–PSE interaction not yet available
    • Mechanism distinguishing Pol II vs Pol III promoter specificity remained unclear
  2. 1998 High

    Demonstration that Oct-1 POU domain directly contacts a specific region of SNAP190 (similar to OBF-1) to cooperatively recruit SNAPc to the PSE explained how enhancer-bound activators stimulate snRNA transcription.

    Evidence Switched-specificity mutagenesis and in vitro transcription

    PMID:9832505

    Open questions at the time
    • Structural basis of the Oct-1/SNAP190 interface not yet resolved at atomic level
  3. 2000 High

    Systematic mapping of subunit–subunit contacts within SNAPc defined which domains of SNAP190 mediate direct interactions with SNAP45 and SNAP43, establishing the internal architecture of the complex.

    Evidence Deletion mapping, pulldown assays, and PSE-binding with minimal domains

    PMID:11056176

    Open questions at the time
    • Three-dimensional arrangement of subunits relative to DNA not known
  4. 2002 High

    Atomic-resolution crystal structure of the Oct-1 POU/octamer/SNAP190 peptide ternary complex, together with identification of a SNAP190 N-terminal region that recruits TBP, revealed dual mechanisms by which SNAP190 bridges activator and basal machinery to snRNA promoters.

    Evidence X-ray crystallography at 2.3 Å; truncation/mutagenesis with cooperative DNA-binding and in vitro U6 transcription

    PMID:12391172 PMID:12414730

    Open questions at the time
    • Redundancy between SNAP190-mediated and Brf2-mediated TBP recruitment not fully dissected in vivo
  5. 2003 High

    Showing that the SNAP190 Myb domain alone suffices to recruit TBP to the U6 TATA box established that PSE recognition and TBP recruitment are mechanistically coupled through the same structural domain.

    Evidence TBP recruitment assay, pulldown, in vitro transcription with domain truncations

    PMID:12621023

    Open questions at the time
    • Role of full-length SNAP190 C-terminal regions in TBP-dependent complex assembly not addressed
  6. 2007 High

    Discovery that CK2 phosphorylates two N-terminal regions of SNAP190 to allosterically inhibit its Myb DNA-binding domain provided the first post-translational regulatory mechanism controlling SNAPc activity.

    Evidence In vitro kinase assay, phosphosite mutagenesis, DNA-binding and U6 transcription assays

    PMID:17670747

    Open questions at the time
    • In vivo regulation by CK2 not demonstrated
    • Conditions or signals triggering CK2-mediated inhibition unknown
  7. 2008 Medium

    RNAi depletion of SNAP190 caused G0/G1 cell-cycle arrest, distinct from the G2/M arrest seen with SNAP45 depletion, revealing subunit-specific cell-cycle consequences of SNAPc disruption.

    Evidence RNAi knockdown in human cells, flow cytometry

    PMID:18356157

    Open questions at the time
    • Mechanism linking snRNA deficiency specifically to G0/G1 arrest not resolved
    • Single lab result
  8. 2012 High

    ChIP-seq showed SNAPC4 occupancy is restricted to snRNA gene loci genome-wide, and photo-cross-linking mapped the topological arrangement of all 4.5 Myb repeats on the PSE, together defining SNAPC4 as an snRNA-gene-specific DNA-recognition module.

    Evidence ChIP-seq in human cells; site-specific protein–DNA photo-cross-linking with Drosophila SNAP190

    PMID:22966203 PMID:23038247

    Open questions at the time
    • Whether the Drosophila Myb–PSE arrangement is conserved in the human complex
  9. 2011 High

    Zebrafish genetic studies revealed that truncating snapc4 mutations and loss of its vertebrate-specific interaction with Snapc2 cause biliary and exocrine pancreatic hypoplasia through altered snRNA expression and apoptosis, establishing developmental requirements for SNAPC4.

    Evidence Zebrafish forward genetic screen, morpholino knockdown, co-IP, snRNA quantification, whole-genome sequencing of ENU mutant

    PMID:22222761 PMID:22496837

    Open questions at the time
    • Specific snRNA targets responsible for tissue-selective phenotypes not identified
    • Whether biliary and pancreatic phenotypes share a common snRNA deficiency mechanism
  10. 2022 High

    Cryo-EM structure of human SNAPc bound to the U6-1 PSE at 3.49 Å resolved the wrap-around DNA-binding mode in which SNAP190 Myb repeats and SNAP50 jointly encircle the PSE, explaining the sequence conservation of PSE motifs.

    Evidence Cryo-EM structure determination

    PMID:36369505

    Open questions at the time
    • Full-length SNAP190 including C-terminal Oct-1 interaction and TBP-recruitment domains not resolved
    • No structure of the complete five-subunit complex on DNA
  11. 2023 High

    Identification of bi-allelic SNAPC4 variants in patients with neuroregression and spastic paraparesis, corroborated by CRISPR depletion showing decreased snRNA levels and global splicing dysregulation, established SNAPC4 deficiency as a human Mendelian neurodegenerative disorder.

    Evidence Human genetics, CRISPR depletion in HeLa, RT-qPCR of snRNAs, transcriptome-wide splicing analysis in patient fibroblasts

    PMID:36965478

    Open questions at the time
    • Which specific snRNAs and mis-spliced transcripts are pathogenic
    • Cell-type-specific vulnerability of neurons to SNAPC4 deficiency not mechanistically explained
  12. 2025 High

    Demonstrating that SUMOylation of SNAPC1 is required for its interaction with SNAPC4 and for basal snRNA transcription revealed a new layer of post-translational control over SNAPc complex integrity.

    Evidence CRISPR/dCas9-SENP1 promoter-targeted deSUMOylation, inducible degron depletion, co-IP of endogenous tagged subunits, snRNA transcription assay

    PMID:40956881

    Open questions at the time
    • Whether SNAPC4 itself is SUMOylated
    • Signals that regulate SNAPC1 SUMOylation status in vivo

Open questions

Synthesis pass · forward-looking unresolved questions
  • A complete structural model of the full five-subunit SNAPc in the context of a Pol II or Pol III pre-initiation complex, and the identity of specific snRNA targets whose deficiency underlies tissue-selective developmental and neurodegenerative phenotypes, remain unresolved.
  • No full-length five-subunit SNAPc structure on DNA
  • Mechanism of Pol II versus Pol III promoter discrimination by SNAPC4-containing complexes not resolved
  • Pathogenic snRNA and splicing targets in human SNAPC4-deficient disease not identified

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0003677 DNA binding 5 GO:0140110 transcription regulator activity 3
Localization
GO:0000228 nuclear chromosome 1 GO:0005634 nucleus 1
Pathway
R-HSA-74160 Gene expression (Transcription) 5 R-HSA-8953854 Metabolism of RNA 2 R-HSA-1640170 Cell Cycle 1
Partners
CSNK2A1POU2F1SNAPC1SNAPC2SNAPC3SNAPC5TBP
Complex memberships
SNAPc (snRNA-activating protein complex)

Evidence

Reading pass · 17 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1998 SNAP190 (SNAPC4) is the largest subunit of SNAPc and contains an unusual Myb DNA-binding domain with four complete repeats (Ra–Rd) and a half repeat (Rh); a truncated protein with only repeats Rc and Rd can bind the PSE, demonstrating that the SNAP190 Myb domain directly contacts the PSE. SNAP190 also interacts with SNAP45 and with Oct-1. cDNA cloning, recombinant protein PSE-binding assay, protein–protein interaction assays (co-immunoprecipitation/pulldown) Molecular and cellular biology High 9418884
1998 SNAPc can be reconstituted from five recombinant subunits (SNAP43, SNAP45, SNAP50, SNAP190, and the newly identified SNAP19) to form a complex that binds specifically to the PSE and directs both RNA polymerase II and III snRNA gene transcription, establishing SNAP190 as an essential core component. Recombinant protein co-expression and reconstitution, PSE-binding assay, in vitro transcription Genes & development High 9732265
1998 The Oct-1 POU domain directly contacts a specific small region of SNAP190 (SNAPC4) to cooperatively recruit SNAPc to the PSE and activate snRNA transcription; a switched-specificity SNAP190 mutant that interacts with Oct-1 POU E7R but not wild-type Oct-1 POU confirmed the direct protein–protein contact. The SNAP190 interacting region is similar to the OBF-1/OCA-B Oct-1 coactivator region. Protein–protein interaction assay, switched-specificity mutagenesis, in vitro transcription Genes & development High 9832505
2000 A detailed map of subunit–subunit contacts within SNAPc was established: SNAP190 (SNAPC4) directly contacts SNAP45 and SNAP43; specific domains required for each pairwise contact were defined, and complexes containing only these minimal interaction domains retain specific PSE-binding activity. Deletion mapping, pulldown/co-immunoprecipitation, PSE-binding assay The Journal of biological chemistry High 11056176
2002 X-ray crystal structure of the Oct-1 POU domain/U1 octamer/SNAP190 peptide ternary complex revealed that the SNAP190 peptide (residues 884–910) makes extensive protein contacts with the Oct-1 POU-specific domain and with DNA phosphate backbone within the enhancer, mechanistically explaining cooperative recruitment of SNAPc by Oct-1. X-ray crystallography (2.3 Å resolution) Genes & development High 12414730
2002 A 50-amino-acid region within the N-terminal third of SNAP190 (SNAPC4) is required for cooperative binding with TBP at the U6 promoter as part of mini-SNAPc (SNAP43 + SNAP50 + N-terminal SNAP190); loss of this region can be compensated by TBP recruitment through Brf2, revealing redundant mechanisms for TBP recruitment to the U6 initiation complex. Truncation/mutagenesis analysis, cooperative DNA-binding assay, in vitro U6 transcription Molecular and cellular biology High 12391172
2003 The SNAP190 (SNAPC4) Myb DNA-binding domain directly interacts with the TBP DNA-binding domain; truncated SNAP190 containing only the Myb domain is sufficient to recruit TBP to the U6 TATA box and to stimulate assembly with Brf2, defining a role for the Myb domain in RNA Pol III pre-initiation complex assembly at juxtaposed promoter elements. TBP recruitment assay, pulldown interaction assay, in vitro transcription The Journal of biological chemistry High 12621023
2006 A partial SNAPc containing SNAP190 (residues 1–505), SNAP50, SNAP43, and SNAP19, co-expressed in E. coli, binds PSE specifically, recruits TBP to U6 promoter DNA, and supports reconstituted transcription of U1 and U6 snRNA genes by RNA Pol II and III respectively, confirming SNAP190 as the PSE-recognizing scaffold of the functional complex. Recombinant co-expression in E. coli, PSE-binding assay, TBP recruitment assay, in vitro transcription Protein expression and purification High 16603380
2007 CK2 phosphorylates the N-terminal half of SNAP190 (SNAPC4) at two regions (amino acids 20–63 and 514–545) containing multiple CK2 consensus sites; this phosphorylation inhibits SNAPc DNA binding and U6 transcription activity, and mutational analyses support an allosteric inhibition of the SNAP190 Myb DNA-binding domain as the mechanism. In vitro kinase assay, phosphorylation site mapping, mutagenesis, DNA-binding assay, in vitro U6 transcription The Journal of biological chemistry High 17670747
2008 Down-regulation of SNAP190 (SNAPC4) by RNAi leads to accumulation of cells with G0/G1 DNA content, whereas down-regulation of SNAP45 causes G2/M arrest, indicating distinct cell-cycle roles for different SNAPc subunits; SNAP190 depletion phenotype is consistent with its role in driving snRNA transcription needed for S-phase entry. RNAi knockdown, flow cytometry cell-cycle analysis The Journal of biological chemistry Medium 18356157
2012 ChIP-seq with anti-SNAPC4 antibody showed that SNAPC4 occupancy is limited to snRNA gene loci genome-wide, while SNAPC1 extends to protein-coding genes, establishing SNAPC4 as an snRNA-gene-specific component of SNAPc in chromatin. Chromatin immunoprecipitation followed by high-throughput sequencing (ChIP-seq) Molecular and cellular biology Medium 22966203
2012 Site-specific protein–DNA photo-cross-linking mapped the topological arrangement of all 4.5 Myb repeats of Drosophila SNAP190 (ortholog of SNAPC4) on a U1 snRNA gene PSE, showing each repeat contacts the DNA and revealing their spatial organization within the SNAPc–DNA complex. Site-specific protein–DNA photo-cross-linking assay The Journal of biological chemistry High 23038247
2011 In zebrafish, a truncating mutation in snapc4 that deletes the C-terminal domain responsible for interaction with Snapc2 (a vertebrate-specific SNAPc subunit) causes apoptosis of biliary epithelial cells and loss of the intrahepatic biliary network; snapc2 knockdown phenocopies this, and the mutant shows altered expression of a subset of snRNAs, linking the Snapc4–Snapc2 physical interaction to snRNA transcription and biliary cell survival. Zebrafish forward genetic screen, morpholino knockdown, co-immunoprecipitation (interaction domain mapping), snRNA quantification, apoptosis assay Developmental biology High 22222761
2012 Whole-genome sequencing of a zebrafish ENU mutant (m1045) identified a nonsense mutation in snapc4; morpholino knockdown confirmed that loss of Snapc4 causes severe exocrine pancreas hypoplasia, establishing a developmental requirement for Snapc4 in exocrine pancreatic organogenesis. Whole-genome sequencing, homozygosity mapping, morpholino knockdown, histology PloS one Medium 22496837
2022 Cryo-EM structure of human SNAPc (N-terminal domain of SNAP190/SNAPC4, SNAP50, and SNAP43) in complex with the U6-1 PSE at 3.49 Å revealed a 'wrap-around' DNA-binding mode; three SNAP50 motifs contact both major and minor grooves of the PSE in coordination with the SNAP190 Myb domain, explaining PSE sequence conservation and SNAPc assembly. Cryo-electron microscopy structure determination (3.49 Å overall resolution) Nature communications High 36369505
2023 Bi-allelic deleterious SNAPC4 variants in humans reduce SNAPC4 protein abundance, decrease snRNA expression levels, and cause global dysregulation of alternative splicing (shown in patient fibroblasts and CRISPR-depleted HeLa cells), leading to neuroregression and progressive spastic paraparesis. Human genetic analysis, CRISPR genomic editing/depletion in HeLa cells, snRNA quantification (RT-qPCR), transcriptome-wide splicing analysis in patient fibroblasts American journal of human genetics High 36965478
2025 SUMOylation-deficient SNAPC1 (2KR mutant) retains interaction with SNAPC3 but has impaired interaction with SNAPC4, and fails to sustain basal snRNA transcription, indicating that SNAPC1 SUMOylation is required for proper SNAPc complex assembly involving SNAPC4 and for snRNA transcriptional activity. CRISPR/dCas9-SENP1 promoter-targeted deSUMOylation, inducible degron depletion of SNAPC1, co-immunoprecipitation of tagged endogenous SNAPC3 and SNAPC4, snRNA transcription assay Proceedings of the National Academy of Sciences of the United States of America High 40956881

Source papers

Stage 0 corpus · 31 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
1998 The large subunit of basal transcription factor SNAPc is a Myb domain protein that interacts with Oct-1. Molecular and cellular biology 82 9418884
2003 STAT5 and Oct-1 form a stable complex that modulates cyclin D1 expression. Molecular and cellular biology 76 14645506
1998 SNAP19 mediates the assembly of a functional core promoter complex (SNAPc) shared by RNA polymerases II and III. Genes & development 73 9732265
2010 Elucidating the chromosome 9 association with AS; CARD9 is a candidate gene. Genes and immunity 59 20463747
1998 The Oct-1 POU domain activates snRNA gene transcription by contacting a region in the SNAPc largest subunit that bears sequence similarities to the Oct-1 coactivator OBF-1. Genes & development 50 9832505
2000 A map of protein-protein contacts within the small nuclear RNA-activating protein complex SNAPc. The Journal of biological chemistry 41 11056176
2002 Redundant cooperative interactions for assembly of a human U6 transcription initiation complex. Molecular and cellular biology 34 12391172
2012 Fast homozygosity mapping and identification of a zebrafish ENU-induced mutation by whole-genome sequencing. PloS one 31 22496837
2003 Inhibition of p53, p21 and Bax by pifithrin-alpha does not affect UV induced apoptotic response in CS-B cells. DNA repair 28 12893085
2020 Implication of m6A mRNA Methylation in Susceptibility to Inflammatory Bowel Disease. Epigenomes 27 34968289
2003 The small nuclear RNA-activating protein 190 Myb DNA binding domain stimulates TATA box-binding protein-TATA box recognition. The Journal of biological chemistry 22 12621023
2015 Determination of IL1 R2, ANTXR2, CARD9, and SNAPC4 single nucleotide polymorphisms in Iranian patients with ankylosing spondylitis. Rheumatology international 20 26590821
2011 Mutation of zebrafish Snapc4 is associated with loss of the intrahepatic biliary network. Developmental biology 18 22222761
2013 Evidence for genetic association of CARD9 and SNAPC4 with ankylosing spondylitis in a Chinese Han population. The Journal of rheumatology 17 24334645
2021 Functional and evolutionary analysis of the Arabidopsis 4R-MYB protein SNAPc4 as part of the SNAP complex. Plant physiology 16 33693812
2006 The unorthodox SNAP50 zinc finger domain contributes to cooperative promoter recognition by human SNAPC. The Journal of biological chemistry 16 16901896
2002 Activator recruitment by the general transcription machinery: X-ray structural analysis of the Oct-1 POU domain/human U1 octamer/SNAP190 peptide ternary complex. Genes & development 16 12414730
2012 Requirement for SNAPC1 in transcriptional responsiveness to diverse extracellular signals. Molecular and cellular biology 15 22966203
2002 Recruitment of the priming protein pTP and DNA binding occur by overlapping Oct-1 POU homeodomain surfaces. The EMBO journal 15 11847120
2007 The protein kinase CK2 phosphorylates SNAP190 to negatively regulate SNAPC DNA binding and human U6 transcription by RNA polymerase III. The Journal of biological chemistry 13 17670747
2022 Identification of the hub genes related to adipose tissue metabolism of bovine. Frontiers in veterinary science 12 36439361
2022 Structural basis of human SNAPc recognizing proximal sequence element of snRNA promoter. Nature communications 11 36369505
2023 Bi-allelic SNAPC4 variants dysregulate global alternative splicing and lead to neuroregression and progressive spastic paraparesis. American journal of human genetics 8 36965478
2006 Co-expression of multiple subunits enables recombinant SNAPC assembly and function for transcription by human RNA polymerases II and III. Protein expression and purification 6 16603380
2012 Architectural arrangement of the small nuclear RNA (snRNA)-activating protein complex 190 subunit (SNAP190) on U1 snRNA gene promoter DNA. The Journal of biological chemistry 5 23038247
2008 Mitotic functions for SNAP45, a subunit of the small nuclear RNA-activating protein complex SNAPc. The Journal of biological chemistry 5 18356157
2024 Genetic overlap between inflammatory bowel disease and iridocyclitis: insights from a genome-wide association study in a European population. BMC genomic data 2 39472800
2002 Crystallization of the Oct-1/SNAP190 peptide/DNA complex. Acta crystallographica. Section D, Biological crystallography 1 11856838
2025 UBE3C promotes pancreatic ductal adenocarcinoma progression by catalysing p53 ubiquitination. Molecular biology reports 0 40553397
2025 SUMO conjugation to promoter-proximal sequence elements-associated proteins impacts on snRNA transcription. Proceedings of the National Academy of Sciences of the United States of America 0 40956881
2024 Multiregion exome sequencing indicates a monoclonal origin of esophageal spindle-cell squamous cell carcinoma. The Journal of pathology 0 39022845