Affinage

SNAPC1

snRNA-activating protein complex subunit 1 · UniProt Q16533

Length
368 aa
Mass
43.0 kDa
Annotated
2026-04-28
23 papers in source corpus 14 papers cited in narrative 14 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

SNAPC1 (SNAP43) is a core subunit of the five-subunit SNAPc complex that binds the proximal sequence element (PSE) of snRNA gene promoters and nucleates preinitiation complex assembly for both RNA polymerase II and RNA polymerase III transcription. Within SNAPc, SNAPC1 directly contacts SNAP50, SNAP190, and TBP, contributing to a 'wrap-around' DNA-binding architecture resolved by cryo-EM, and its SUMOylation at K245 and K333 is required for interaction with SNAPC4 and for sustaining basal snRNA transcription (PMID:7715707, PMID:36369505, PMID:40956881). Beyond snRNA genes, SNAPC1 associates with elongating RNA polymerase II at protein-coding genes genome-wide and is required for transcriptional responsiveness to extracellular signals such as EGF and retinoic acid, establishing it as a general transcriptional coactivator (PMID:22966203). SNAPC1 thus operates at two levels: as a PSE-recognition scaffold essential for snRNA gene expression, and as an elongation-associated factor modulating signal-dependent transcription of mRNA genes.

Mechanistic history

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

    Identification of SNAPC1 as a subunit of a novel TBP-containing complex (SNAPc) that binds the PSE and is required for both Pol II and Pol III snRNA transcription established the fundamental biochemical framework for understanding snRNA promoter recognition.

    Evidence Biochemical purification, EMSA, and in vitro transcription from human cell extracts

    PMID:7715707 PMID:8633057

    Open questions at the time
    • Structural basis of PSE recognition unknown
    • No information on in vivo relevance or genome-wide occupancy
    • Role of individual subunits in DNA contact not resolved
  2. 1996 High

    Mapping of direct subunit contacts — SNAP50 interacts with SNAP43 but not SNAP45 or TBP — provided the first internal architecture of SNAPc and defined SNAPC1 as a central bridging subunit.

    Evidence UV cross-linking to DNA and co-immunoprecipitation of recombinant subunits

    PMID:9003788

    Open questions at the time
    • Full five-subunit interaction network not yet mapped
    • DNA contacts by SNAPC1 itself not assessed
  3. 1998 High

    Reconstitution of a complete five-subunit recombinant SNAPc (SNAP19, SNAP43, SNAP45, SNAP50, SNAP190) that binds the PSE and directs both Pol II and Pol III snRNA transcription demonstrated that no additional factors are needed for SNAPc function and confirmed SNAPC1 as an essential structural component.

    Evidence Recombinant protein co-expression, EMSA, in vitro transcription

    PMID:9418884 PMID:9732265

    Open questions at the time
    • How the same complex directs two different polymerases remained unclear
    • Contribution of individual subunit domains to transcription not delineated
  4. 2000 High

    Systematic domain-mapping of all pairwise subunit contacts within SNAPc, including SNAPC1, showed that minimal interaction domains are sufficient for PSE binding, establishing that direct protein–protein contacts underpin DNA recognition.

    Evidence Co-immunoprecipitation of truncation/deletion mutants combined with EMSA

    PMID:11056176

    Open questions at the time
    • No high-resolution structural information
    • Post-translational modifications not explored
  5. 2003 High

    Demonstration that both SNAPC1 and SNAP190 directly contact the TBP DNA-binding domain defined the assembly pathway for the Pol III preinitiation complex and established SNAPC1's role in TBP recruitment.

    Evidence TBP recruitment assays, co-immunoprecipitation, and EMSA with truncation mutants

    PMID:12391172 PMID:12621023

    Open questions at the time
    • Structural details of TBP–SNAPC1 interface unknown
    • Whether SNAPC1–TBP contact is required for Pol II snRNA transcription not tested
  6. 2004 Medium

    Photo-cross-linking of the Drosophila SNAPC1 ortholog to PSE DNA revealed polymerase-specific differences in DNA contacts, supporting a model in which PSE-dependent conformational changes in SNAPc determine Pol II vs. Pol III recruitment.

    Evidence Photo-cross-linking and EMSA in Drosophila S2 cells

    PMID:14966271

    Open questions at the time
    • Observation in Drosophila; relevance to human SNAPC1 not confirmed
    • Conformational change inferred indirectly from cross-linking pattern
  7. 2012 High

    ChIP-seq discovery that SNAPC1 occupies protein-coding genes genome-wide and tracks with elongating Pol II, combined with depletion experiments showing impaired EGF and retinoic acid transcriptional responses, revealed an unexpected second role for SNAPC1 as a general transcriptional coactivator beyond snRNA genes.

    Evidence ChIP-seq, RNAi depletion, elongation inhibition, and gene expression profiling in human cells

    PMID:22966203

    Open questions at the time
    • Mechanism by which SNAPC1 promotes elongation unknown
    • Whether this function requires other SNAPc subunits not established
    • Direct protein–protein contacts linking SNAPC1 to the elongation machinery not identified
  8. 2022 High

    A 3.49 Å cryo-EM structure of the SNAP190–SNAP50–SNAP43 sub-complex bound to the U6-1 PSE resolved the 'wrap-around' DNA recognition mode, explaining PSE sequence conservation and providing the first high-resolution view of SNAPC1 within the assembled complex.

    Evidence Cryo-electron microscopy of reconstituted human SNAPc–PSE complex

    PMID:36369505

    Open questions at the time
    • Structure lacks SNAP19 and SNAP45 subunits
    • No structure of full preinitiation complex with TBP or polymerase
    • SNAPC1 DNA contacts not individually resolved in this structure
  9. 2025 High

    Identification of K245 and K333 as SUMOylation sites on SNAPC1, with demonstration that SUMOylation is required for SNAPC4 interaction and for sustaining basal snRNA transcription, established post-translational modification as a regulatory layer controlling SNAPc assembly and activity.

    Evidence CRISPR/dCas9-SENP1 targeting, site-directed mutagenesis, inducible degron depletion, co-immunoprecipitation, in vivo transcription assays

    PMID:40956881

    Open questions at the time
    • Whether SUMOylation affects SNAPC1 function at protein-coding genes is unknown
    • SUMO E3 ligase responsible for SNAPC1 modification not identified
    • Dynamics of SUMOylation during the cell cycle or signaling not explored

Open questions

Synthesis pass · forward-looking unresolved questions
  • Key unresolved questions include how SNAPC1 mechanistically promotes transcriptional elongation at protein-coding genes, whether it functions independently of other SNAPc subunits in that context, and how its SUMOylation is regulated in response to physiological signals.
  • No reconstituted elongation assay with SNAPC1
  • Full SNAPc structure with all five subunits and bound polymerase not available
  • Relationship between SNAPc-dependent and SNAPc-independent functions of SNAPC1 unresolved

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0003677 DNA binding 3 GO:0060090 molecular adaptor activity 2 GO:0140110 transcription regulator activity 1
Localization
GO:0005634 nucleus 3
Pathway
R-HSA-8953854 Metabolism of RNA 3
Partners
SNAPC2SNAPC3SNAPC4SNAPC5TBP
Complex memberships
SNAPc

Evidence

Reading pass · 14 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1995 SNAPc (containing SNAP43/SNAPC1, SNAP45, SNAP50, and TBP) is a TBP-TAF complex required for transcription of both RNA polymerase II and III snRNA genes; it binds specifically to the proximal sequence element (PSE), a non-TATA-box basal promoter element common to both gene types. Biochemical purification, EMSA, in vitro transcription assay Nature High 7715707
1996 SNAP43 (SNAPC1) is a subunit of SNAPc that is required for both RNA polymerase II and III transcription of snRNA genes; antibodies against SNAP45 (which interacts with SNAP43) retard SNAPc-PSE complex mobility, confirming subunit composition. Immunodepletion, EMSA, in vitro transcription assay, co-immunoprecipitation Proceedings of the National Academy of Sciences of the United States of America High 8633057
1996 SNAP50 contacts DNA within the SNAP complex (UV cross-linking) and interacts with SNAP43 (SNAPC1) by co-immunoprecipitation, but not with SNAP45 or TBP, defining initial SNAPc architecture. UV cross-linking, co-immunoprecipitation, in vitro transcription assay The EMBO journal High 9003788
1998 SNAP19 is a fifth SNAPc subunit that, together with SNAP43, SNAP45, SNAP50, and SNAP190, assembles a recombinant SNAPc that binds the PSE and directs both RNA polymerase II and III snRNA gene transcription, demonstrating that the same core SNAPc nucleates two classes of initiation complexes. Recombinant protein reconstitution, EMSA, in vitro transcription assay Genes & development High 9732265
1998 SNAP190, the largest SNAPc subunit, contains a Myb DNA-binding domain (four complete repeats plus a half repeat) that contributes to PSE recognition; SNAP190 interacts with SNAP45 and with the Oct-1 activator, and is required for snRNA gene transcription by both RNA polymerases II and III. cDNA cloning, EMSA with truncation mutants, co-immunoprecipitation, in vitro transcription assay Molecular and cellular biology High 9418884
2000 A detailed map of protein-protein contacts within SNAPc was established: specific subunit domains required for subunit-subunit association were defined, and complexes containing only those interaction domains retain specific PSE binding, indicating that direct subunit contacts are sufficient for DNA recognition. Co-immunoprecipitation with deletion/truncation mutants, EMSA The Journal of biological chemistry High 11056176
2002 A 50-amino-acid region within SNAP190 mediates cooperative binding with TBP in the context of mini-SNAPc (SNAP43, SNAP50, and N-terminal SNAP190); mini-SNAPc derivatives lacking this region remain transcriptionally active because TBP can still be recruited via cooperative interactions with Brf2, revealing redundant mechanisms for TBP recruitment to the U6 promoter. Promoter binding assays with truncation mutants, in vitro transcription assay, recombinant protein reconstitution Molecular and cellular biology High 12391172
2003 Two SNAPc subunits, SNAP43 (SNAPC1) and SNAP190, directly interact with the TBP DNA-binding domain; the SNAP190 Myb domain is sufficient to recruit TBP to the U6 TATA box and stimulates SNAP190-TBP-Brf2 complex assembly, defining the assembly pathway of the RNA polymerase III-specific preinitiation complex. TBP recruitment assays, co-immunoprecipitation, EMSA with truncation mutants The Journal of biological chemistry High 12621023
2004 In Drosophila, the SNAPC1 ortholog DmPBP45 (identified by sequence similarity to human SNAP43) contacts DNA differentially depending on PSE sequence: it cross-links strongly for two turns downstream of the U1 PSE but only a half turn downstream of the U6 PSE, consistent with a model in which PSE-dependent conformational differences in the DmPBP complex determine RNA polymerase specificity. Photo-cross-linking, S2 cell expression, EMSA Molecular and cellular biology Medium 14966271
2006 The SNAP50 zinc finger domain (eight cysteine/histidine residues identified by alanine scanning) plays an important role in PSE DNA binding by SNAPc; metal binding studies revealed a single zinc atom, indicating one functional coordination site; four cysteine residues essential for DNA binding were also required for both U1 (Pol II) and U6 (Pol III) transcription, while the remaining four residues showed differential effects on Pol II vs Pol III transcription. Alanine scanning mutagenesis, metal binding assays, EMSA, in vitro transcription assay The Journal of biological chemistry High 16901896
2006 A partial SNAPc (SNAP190[1-505], SNAP50, SNAP43/SNAPC1, and SNAP19) co-expressed in E. coli binds PSE DNA specifically, recruits TBP to U6 promoter DNA, and supports transcription of both human U1 and U6 snRNA genes by RNA polymerases II and III, respectively. Recombinant co-expression in E. coli, EMSA, TBP recruitment assay, reconstituted in vitro transcription Protein expression and purification High 16603380
2012 ChIP-seq revealed that SNAPC1 occupancy extends beyond snRNA genes to include a large number of transcriptionally active protein-coding genes, co-localizing with elongating RNA polymerase II; inhibition of transcriptional elongation caused loss of SNAPC1 from gene 3' ends; depletion of SNAPC1 specifically diminished transcriptional responsiveness of many genes to EGF and retinoic acid stimulation, identifying SNAPC1 as a general transcriptional coactivator functioning through elongating RNAPII. ChIP-seq, RNA interference/depletion, transcriptional elongation inhibition, gene expression analysis Molecular and cellular biology High 22966203
2022 Cryo-EM structure of human SNAPc (SNAP190 N-terminal domain, SNAP50, and SNAP43/SNAPC1) bound to the U6-1 PSE at 3.49 Å resolution revealed a 'wrap-around' assembly mode; three SNAP50 motifs contact both major and minor grooves of PSE in coordination with the SNAP190 Myb domain, explaining PSE sequence conservation and SNAPc recognition specificity. Cryo-electron microscopy structural determination Nature communications High 36369505
2025 SNAPC1 is SUMOylated at lysine residues K245 and K333; a SUMOylation-deficient mutant (SNAPC1 2KR) cannot sustain basal snRNA transcription despite being recruited to the PSE; SNAPC1 SUMOylation is required for its interaction with SNAPC4 but not SNAPC3, indicating that SUMO modification controls SNAPc complex assembly and snRNA transcriptional activity. CRISPR/dCas9-SENP1 targeting, site-directed mutagenesis, inducible degron depletion system, co-immunoprecipitation, in vivo transcription assay Proceedings of the National Academy of Sciences of the United States of America High 40956881

Source papers

Stage 0 corpus · 23 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2006 Identification of differentially expressed genes in HPV-positive and HPV-negative oropharyngeal squamous cell carcinomas. European journal of cancer (Oxford, England : 1990) 150 17079134
1995 A TBP-TAF complex required for transcription of human snRNA genes by RNA polymerase II and III. Nature 128 7715707
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 The SNAP45 subunit of the small nuclear RNA (snRNA) activating protein complex is required for RNA polymerase II and III snRNA gene transcription and interacts with the TATA box binding protein. Proceedings of the National Academy of Sciences of the United States of America 52 8633057
1996 Cloning and characterization of SNAP50, a subunit of the snRNA-activating protein complex SNAPc. The EMBO journal 51 9003788
2000 A map of protein-protein contacts within the small nuclear RNA-activating protein complex SNAPc. The Journal of biological chemistry 41 11056176
2002 Discovery of over-expressed genes and genetic alterations in breast cancer cells using a combination of suppression subtractive hybridization, multiplex FISH and comparative genomic hybridization. International journal of oncology 40 12168092
2004 Architectural arrangement of cloned proximal sequence element-binding protein subunits on Drosophila U1 and U6 snRNA gene promoters. Molecular and cellular biology 35 14966271
2002 Redundant cooperative interactions for assembly of a human U6 transcription initiation complex. Molecular and cellular biology 34 12391172
2010 Onconase responsive genes in human mesothelioma cells: implications for an RNA damaging therapeutic agent. BMC cancer 28 20137089
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
2018 Regulation of RNA polymerase III transcription during transformation of human IMR90 fibroblasts with defined genetic elements. Cell cycle (Georgetown, Tex.) 19 29171785
2022 Corticosterone-mediated regulation and functions of miR-218-5p in rat brain. Scientific reports 17 34996981
2021 Rare protein-coding variants implicate genes involved in risk of suicide death. American journal of medical genetics. Part B, Neuropsychiatric genetics : the official publication of the International Society of Psychiatric Genetics 17 34042246
2006 The unorthodox SNAP50 zinc finger domain contributes to cooperative promoter recognition by human SNAPC. The Journal of biological chemistry 16 16901896
2012 Requirement for SNAPC1 in transcriptional responsiveness to diverse extracellular signals. Molecular and cellular biology 15 22966203
2022 Structural basis of human SNAPc recognizing proximal sequence element of snRNA promoter. Nature communications 11 36369505
2014 Mapping of a chromosome 12 region associated with airway hyperresponsiveness in a recombinant congenic mouse strain and selection of potential candidate genes by expression and sequence variation analyses. PloS one 6 25111050
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
2023 [Read-through circular RNA rt-circ-HS promotes hypoxia inducible factor 1α expression and renal carcinoma cell proliferation, migration and invasiveness]. Beijing da xue xue bao. Yi xue ban = Journal of Peking University. Health sciences 2 37042131
1998 The human PTFgamma/SNAP43 gene: structure, chromosomal location, and identification of a VNTR in 5'-UTR. Journal of biochemistry 2 9644240
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