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SNAPC3

snRNA-activating protein complex subunit 3 · UniProt Q92966

Length
411 aa
Mass
46.8 kDa
Annotated
2026-06-10
25 papers in source corpus 10 papers cited in narrative 10 extracted findings
Cross-family judge vs UniProt: tie faithfulness: 5/5 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

SNAPC3 (SNAP50) is an essential DNA-contacting core subunit of the snRNA-activating protein complex (SNAPc), a TBP-containing general transcription factor that binds the proximal sequence element (PSE) of snRNA promoters and is required for transcription of both RNA polymerase II and III snRNA genes (PMID:7715707, PMID:9732265). Within the assembled five-subunit complex, SNAP50 makes direct sequence-specific contacts with PSE DNA through an unorthodox zinc finger domain that, despite containing 15 candidate cysteine/histidine residues across two potential coordination arrangements, binds only a single zinc atom; eight of these residues are critical for SNAPc DNA binding and a subset is essential for both U1 (Pol II) and U6 (Pol III) transcription (PMID:9003788, PMID:16901896). SNAP50 recognizes the PSE through both major- and minor-groove contacts in coordination with the SNAP190 Myb domain in a 'wrap-around' binding mode, and participates in the cooperative recruitment of TBP to the U6 TATA box (PMID:12391172, PMID:36369505). SNAP50 directly associates with SNAP43 (SNAPC1), an interaction that is independent of SNAPC1 SUMOylation status (PMID:9003788, PMID:40956881). The role of SNAP50-like subunits in snRNA gene transcription is evolutionarily conserved (PMID:12486231).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 1995 High

    Establishing that snRNA promoters require a dedicated factor answered how PSE-driven genes are transcribed by two different polymerases, identifying SNAP50 as a subunit of the PSE-binding SNAPc complex.

    Evidence Biochemical purification and in vitro transcription assays

    PMID:7715707

    Open questions at the time
    • Did not resolve which subunit contacts DNA
    • Subunit stoichiometry and individual roles undefined
  2. 1996 High

    Cloning and cross-linking determined that SNAP50 itself directly contacts PSE DNA and is functionally required, distinguishing it from purely scaffolding subunits.

    Evidence cDNA cloning, UV cross-linking, antibody depletion with in vitro transcription readout, and co-immunoprecipitation

    PMID:9003788

    Open questions at the time
    • Zinc finger metal coordination not directly demonstrated
    • Specific DNA-contacting residues not mapped
  3. 1998 High

    Full reconstitution from five recombinant subunits established SNAP50 as an essential core subunit rather than a co-purifying contaminant.

    Evidence Recombinant five-subunit reconstitution with PSE binding and in vitro transcription

    PMID:9732265

    Open questions at the time
    • Did not map subunit-subunit contact surfaces
    • No structural detail of DNA recognition
  4. 2000 Medium

    Domain mapping defined the minimal SNAP50 regions required for assembly into a PSE-binding-competent complex, clarifying the architecture of subunit interactions.

    Evidence Co-immunoprecipitation, deletion/domain mapping, PSE binding assays

    PMID:11056176

    Open questions at the time
    • Single-lab mapping without structural confirmation
    • Interaction interfaces inferred, not visualized
  5. 2002 High

    A minimal SNAP43/SNAP50/SNAP190 complex showed SNAP50 participates in cooperative TBP recruitment to the U6 TATA box, linking PSE binding to TATA-element promoter engagement.

    Evidence Recombinant mini-complex assembly, TBP recruitment assays, in vitro transcription

    PMID:12391172

    Open questions at the time
    • Mechanism of SNAP50-TBP cooperativity not structurally defined
  6. 2002 Medium

    Identification of an orthologous 57 kDa subunit in trypanosome PBP-1 demonstrated that the SNAP50 function in snRNA transcription is deeply conserved.

    Evidence Biochemical purification, gene cloning, sequence/structural homology analysis

    PMID:12486231

    Open questions at the time
    • Functional equivalence inferred from homology
    • Conservation of DNA-contact residues not tested
  7. 2006 High

    Systematic mutagenesis defined the SNAP50 zinc finger as an unorthodox single-zinc domain and identified the residues critical for DNA binding versus transcription, mechanistically separating these functions.

    Evidence Alanine-scanning mutagenesis, metal binding studies, PSE DNA binding and in vitro transcription assays

    PMID:16603380 PMID:16901896

    Open questions at the time
    • Three-dimensional fold of the zinc finger not yet resolved
    • Suppression by TFIIIB cooperativity mechanism unclear
  8. 2022 High

    The cryo-EM structure of mini-SNAPc on the PSE revealed how SNAP50 reads DNA, showing three motifs engaging both grooves alongside the SNAP190 Myb domain in a wrap-around mode.

    Evidence Cryo-EM structure of mini-SNAPc-PSE at 3.49 Å

    PMID:36369505

    Open questions at the time
    • Structure limited to a partial complex lacking SNAP45 and SNAP19
    • TBP/TATA-bound state not captured
  9. 2025 Medium

    Endogenous-tag co-IP with a SUMOylation-deficient SNAPC1 showed SNAP50-SNAPC1 contact is SUMO-independent while SNAPC4 interaction is SUMO-sensitive, refining how post-translational modification shapes complex assembly.

    Evidence Endogenous tagging and co-immunoprecipitation with SUMOylation-deficient SNAPC1 (2KR) mutant

    PMID:40956881

    Open questions at the time
    • Single-lab finding
    • Functional consequence of SUMO-dependent SNAPC4 interaction on transcription not established

Open questions

Synthesis pass · forward-looking unresolved questions
  • How SNAP50-mediated PSE recognition is integrated with full holo-SNAPc assembly and differential recruitment of Pol II versus Pol III machinery in vivo remains open.
  • No structure of the complete five-subunit SNAPc on promoter DNA
  • Determinants of Pol II versus Pol III specificity downstream of SNAP50 binding unresolved

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0003677 DNA binding 3 GO:0140110 transcription regulator activity 3
Localization
GO:0005634 nucleus 2
Pathway
R-HSA-74160 Gene expression (Transcription) 3
Partners
SNAP190SNAPC1SNAPC4TBP
Complex memberships
SNAPc

Evidence

Reading pass · 10 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1995 SNAP50 (SNAPC3) is a subunit of SNAPc, a TBP-TAF complex that binds specifically to the proximal sequence element (PSE) and is required for transcription of both RNA polymerase II and III snRNA genes. Biochemical purification, transcription assays in vitro Nature High 7715707
1996 SNAP50 (SNAPC3) contains two potential zinc finger motifs and directly contacts DNA within the SNAPc-PSE complex, as shown by UV cross-linking; antibody depletion of SNAP50 inhibits both RNA polymerase II and III snRNA gene transcription in vitro. SNAP50 interacts with SNAP43 (SNAPC1) by co-immunoprecipitation but not with SNAP45 or TBP. cDNA cloning, UV cross-linking, co-immunoprecipitation, antibody depletion/transcription assays The EMBO journal High 9003788
1998 SNAPc can be reconstituted from five recombinant subunits (SNAP43, SNAP45, SNAP50, SNAP190, and SNAP19); this recombinant complex binds specifically to the PSE and directs both RNA polymerase II and III snRNA gene transcription, establishing SNAP50 as an essential core subunit. Recombinant protein reconstitution, PSE binding assay, in vitro transcription Genes & development High 9732265
2000 Subunit-subunit interaction mapping within SNAPc revealed specific domains required for SNAP50 to associate with other subunits; complexes containing only the mapped interaction domains retain specific PSE binding. Co-immunoprecipitation, deletion/domain mapping, PSE binding assays The Journal of biological chemistry Medium 11056176
2002 A mini-SNAPc composed of SNAP43, SNAP50, and the N-terminal third of SNAP190 binds cooperatively with TBP to the core U6 promoter and supports transcription; SNAP50 participates in cooperative TBP recruitment to the U6 TATA box. Recombinant mini-complex assembly, TBP recruitment assays, in vitro transcription Molecular and cellular biology High 12391172
2002 The 57 kDa subunit of the trypanosome PBP-1 transcription factor complex is orthologous to human SNAP50, indicating an evolutionarily conserved role for SNAP50-like subunits in snRNA gene transcription across large evolutionary distances. Biochemical purification, gene cloning, sequence/structural homology analysis Proceedings of the National Academy of Sciences of the United States of America Medium 12486231
2006 The SNAP50 zinc finger domain contains 15 cysteine and histidine residues in two potential zinc coordination arrangements, but binds only a single zinc atom; eight residues are critical for DNA binding by SNAPc, four of which are also essential for both U1 (RNA Pol II) and U6 (RNA Pol III) transcription. Defects in DNA binding caused by mutations in four residues can be suppressed by cooperative DNA binding with TFIIIB. Alanine-scanning mutagenesis, metal binding studies, PSE DNA binding assays, in vitro transcription The Journal of biological chemistry High 16901896
2006 A partial SNAPc comprising SNAP190(1-505), SNAP50, SNAP43, and SNAP19 co-expressed in E. coli binds PSE specifically, recruits TBP to U6 promoter DNA, and supports transcription of both human U1 and U6 snRNA genes by RNA polymerases II and III. Bacterial co-expression, PSE binding assay, TBP recruitment assay, reconstituted in vitro transcription Protein expression and purification High 16603380
2022 Cryo-EM structure of human mini-SNAPc (N-terminal domain of SNAP190, SNAP50, and SNAP43) bound to the U6-1 PSE at 3.49 Å resolution reveals that SNAP50 contributes three important motifs involved in both major groove and minor groove recognition of the PSE, acting in coordination with the SNAP190 Myb domain, with a 'wrap-around' binding mode. Cryo-electron microscopy structure determination, structural analysis of protein-DNA contacts Nature communications High 36369505
2025 SUMOylation-deficient SNAPC1 (2KR mutant) retains the ability to interact with SNAPC3 (SNAP50) but shows impaired interaction with SNAPC4, indicating that SNAPC3 interaction with SNAPC1 is independent of SNAPC1 SUMOylation status. Endogenous tagging of SNAPC3 and SNAPC4, co-immunoprecipitation with SUMOylation-deficient SNAPC1 mutant Proceedings of the National Academy of Sciences of the United States of America Medium 40956881

Source papers

Stage 0 corpus · 25 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
1995 A TBP-TAF complex required for transcription of human snRNA genes by RNA polymerase II and III. Nature 128 7715707
2009 Histone acetylations mark origins of polycistronic transcription in Leishmania major. BMC genomics 115 19356248
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
1998 SNAP19 mediates the assembly of a functional core promoter complex (SNAPc) shared by RNA polymerases II and III. Genes & development 73 9732265
1996 Cloning and characterization of SNAP50, a subunit of the snRNA-activating protein complex SNAPc. The EMBO journal 51 9003788
2019 Expression of MHC class I, HLA-A and HLA-B identifies immune-activated breast tumors with favorable outcome. Oncoimmunology 46 31646075
2002 RNA polymerase II-dependent transcription in trypanosomes is associated with a SNAP complex-like transcription factor. Proceedings of the National Academy of Sciences of the United States of America 46 12486231
2000 A map of protein-protein contacts within the small nuclear RNA-activating protein complex SNAPc. The Journal of biological chemistry 41 11056176
2021 Profiles of immune cell infiltration and immune-related genes in the tumor microenvironment of osteosarcoma cancer. BMC cancer 40 34922489
2021 DNA methylation mediates the association between breastfeeding and early-life growth trajectories. Clinical epigenetics 37 34937578
2004 The Trypanosoma brucei spliced leader RNA and rRNA gene promoters have interchangeable TbSNAP50-binding elements. Nucleic acids research 36 14757834
2002 Redundant cooperative interactions for assembly of a human U6 transcription initiation complex. Molecular and cellular biology 34 12391172
2014 Dual-trait selection for ethanol consumption and withdrawal: genetic and transcriptional network effects. Alcoholism, clinical and experimental research 28 25581648
2004 Molecular hierarchy in neurons differentiated from mouse ES cells containing a single human chromosome 21. Biochemical and biophysical research communications 22 14733910
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
2006 The unorthodox SNAP50 zinc finger domain contributes to cooperative promoter recognition by human SNAPC. The Journal of biological chemistry 16 16901896
2022 Structural basis of human SNAPc recognizing proximal sequence element of snRNA promoter. Nature communications 12 36369505
2013 Genomic analysis of sequence-dependent DNA curvature in Leishmania. PloS one 8 23646176
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
2004 Failure to detect binding of Trypanosoma brucei SNAPc to U2 and U6 snRNA gene sequences by in vitro transcription competition and pull-down assays. Molecular and biochemical parasitology 5 15383299
2025 Integrating genetic and transcriptomic data to identify genes underlying obesity risk loci. International journal of obesity (2005) 2 41006818
2024 Integrating Genetic and Transcriptomic Data to Identify Genes Underlying Obesity Risk Loci. medRxiv : the preprint server for health sciences 2 38903089
2021 TBP and SNAP50 transcription factors bind specifically to the Pr77 promoter sequence from trypanosomatid non-LTR retrotransposons. Parasites & vectors 1 34108018
2025 A Systematic, Evidence-Based Workflow for Classifying KMT2A Fusions in Acute Myeloid Leukemia. The Journal of molecular diagnostics : JMD 0 40706988
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

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