Affinage

SNAPC1

snRNA-activating protein complex subunit 1 · UniProt Q16533

Length
368 aa
Mass
43.0 kDa
Annotated
2026-06-10
23 papers in source corpus 13 papers cited in narrative 13 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 5/5 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

SNAPC1 (SNAP43) is a core subunit of the SNAPc (PTF) complex, a TBP-containing assembly that binds the proximal sequence element (PSE) to direct transcription of snRNA genes by both RNA polymerase II and III (PMID:7715707, PMID:9732265). Within SNAPc, SNAP43 contacts SNAP50 and the N-terminal region of SNAP190 to form a minimal PSE-binding module, and cryo-EM of this mini-SNAPc on the U6 PSE reveals a 'wrap-around' DNA recognition mode in which SNAP50 motifs and the SNAP190 Myb domain engage both grooves of the element (PMID:9003788, PMID:12391172, PMID:36369505). SNAP43 also directly contacts the TBP DNA-binding domain, contributing to TBP recruitment and assembly of an RNA polymerase III-specific preinitiation complex on the U6 promoter (PMID:12621023). SUMOylation of SNAPC1 at K245 and K333 is required for its interaction with SNAPC4 and for sustained basal snRNA transcription, linking a post-translational modification to proper complex assembly (PMID:40956881). Beyond snRNA genes, SNAPC1 occupies transcriptionally active protein-coding loci genome-wide, tracking with elongating RNA polymerase II across gene bodies and 3' ends, and its depletion blunts transcriptional responses to EGF and retinoic acid, establishing a broader role as a general transcriptional coactivator (PMID:22966203).

Mechanistic history

Synthesis pass · year-by-year structured walk · 11 steps
  1. 1995 High

    Established SNAP43 as a subunit of a PSE-binding TBP-TAF complex required for snRNA gene transcription by both Pol II and Pol III, defining the foundational machinery.

    Evidence Biochemical purification of SNAPc/PTF, PSE-binding and in vitro transcription assays

    PMID:7715707

    Open questions at the time
    • Individual subunit contributions not yet resolved
    • No structural detail of PSE recognition
  2. 1996 High

    Defined the immediate protein neighborhood of SNAP43 within SNAPc and confirmed its functional requirement, showing it binds SNAP50 but not SNAP45 or TBP directly.

    Evidence Antibody depletion plus in vitro transcription and co-immunoprecipitation; companion work placing SNAP45 as the TBP-contacting subunit

    PMID:8633057 PMID:9003788

    Open questions at the time
    • Did not map contact domains
    • Subunit stoichiometry undefined
  3. 1998 High

    Demonstrated that a defined five-subunit recombinant SNAPc is sufficient for specific PSE binding and snRNA transcription, proving the complete subunit roster.

    Evidence Recombinant reconstitution from SNAP43/45/50/190/19 with PSE binding and in vitro transcription

    PMID:9732265

    Open questions at the time
    • No structural model
    • Mechanism distinguishing Pol II vs Pol III recruitment unresolved
  4. 2000 Medium

    Mapped the minimal subunit-subunit contact architecture, showing interaction domains alone reconstitute PSE-specific binding.

    Evidence Deletion mapping with co-IP and EMSA PSE-binding readout

    PMID:11056176

    Open questions at the time
    • Single-lab mapping
    • Atomic detail of contacts unknown
  5. 2002 High

    Showed that a mini-SNAPc (SNAP43, SNAP50, SNAP190 N-terminus) binds the U6 promoter cooperatively with TBP, identifying the minimal transcriptionally competent module.

    Evidence Recombinant mini-SNAPc reconstitution, PSE/TATA binding and in vitro transcription

    PMID:12391172

    Open questions at the time
    • Direct SNAP43-TBP contact not yet established
    • No structure of the cooperative complex
  6. 2003 Medium

    Identified a direct SNAP43-TBP interaction contributing to TBP recruitment, clarifying how SNAPc assembles a Pol III preinitiation complex on the U6 TATA box.

    Evidence TBP recruitment and direct interaction assays with reconstituted mini-SNAPc

    PMID:12621023

    Open questions at the time
    • Single-lab finding
    • Interplay with SNAP45-TBP contact not reconciled
  7. 2004 Medium

    Provided a mechanistic basis for polymerase selectivity by showing the SNAP43 ortholog adopts distinct conformations on U1 versus U6 PSEs.

    Evidence Photo-cross-linking of Drosophila DmPBP45 on U1/U6 PSEs in S2 cells

    PMID:14966271

    Open questions at the time
    • Demonstrated in ortholog, not human
    • Conformation-to-polymerase link inferred, not directly shown
  8. 2006 Medium

    Confirmed SNAP43 participates in direct DNA contacts and that an E. coli-expressed partial SNAPc recapitulates PSE binding, TBP recruitment and snRNA transcription.

    Evidence E. coli co-expression of partial SNAPc, PSE binding, TBP recruitment and reconstituted transcription

    PMID:16603380

    Open questions at the time
    • Single-lab reconstitution
    • Precise SNAP43 DNA contact residues not defined
  9. 2012 High

    Expanded SNAPC1 function beyond snRNA genes by showing genome-wide occupancy at active protein-coding genes coupled to elongating Pol II and required for stimulus-responsive transcription.

    Evidence ChIP-seq, siRNA/shRNA depletion with EGF/RA responsiveness assays and elongation-inhibitor treatment

    PMID:22966203

    Open questions at the time
    • Whether coactivator role uses the full SNAPc complex unclear
    • Direct partners at protein-coding genes unidentified
  10. 2022 High

    Resolved the atomic basis of PSE recognition, visualizing mini-SNAPc in a wrap-around mode on the U6 PSE with SNAP43 directly in the assembly.

    Evidence Cryo-EM of human mini-SNAPc on U6-1 PSE at 3.49 Å

    PMID:36369505

    Open questions at the time
    • Full five-subunit complex not resolved
    • No structure with TBP or polymerase bound
  11. 2025 High

    Established SUMOylation of SNAPC1 as a regulatory layer required for SNAPC4 interaction, complex assembly and sustained snRNA transcription.

    Evidence dCas9-SENP1 targeted deSUMOylation, K245R/K333R mutagenesis, degron depletion, co-IP and ChIP with snRNA readout

    PMID:40956881

    Open questions at the time
    • SUMO E3 ligase responsible unidentified
    • Whether SUMOylation regulates protein-coding coactivator role unknown
    • Structural consequence of SUMOylation on SNAPC4 binding unresolved

Open questions

Synthesis pass · forward-looking unresolved questions
  • How SNAPc conformation and PSE geometry select between RNA polymerase II and III in human cells, and how SNAPC1's coactivator role at protein-coding genes is integrated with its snRNA function, remain unresolved.
  • No human structure capturing polymerase-specific recruitment
  • Mechanism connecting elongation-coupled occupancy to coactivation undefined

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0003677 DNA binding 2 GO:0140110 transcription regulator activity 2 GO:0140223 general transcription initiation factor activity 2
Localization
GO:0005634 nucleus 2
Pathway
R-HSA-74160 Gene expression (Transcription) 3
Partners
SNAP190SNAP50SNAPC3SNAPC4TBP
Complex memberships
SNAPc/PTF

Evidence

Reading pass · 13 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1995 SNAPC1 (SNAP43) was identified as a subunit of the SNAPc (also called PTF) complex, which is a TBP-TAF complex required for transcription of both RNA polymerase II and III snRNA genes. SNAPc binds specifically to the proximal sequence element (PSE), a non-TATA-box basal promoter element common to both gene types. Biochemical purification, TBP-TAF complex characterization, PSE-binding assay, in vitro transcription Nature High 7715707
1996 SNAPC1 (SNAP43) is required for both RNA polymerase II and III transcription of snRNA genes in vitro. SNAP43 interacts with SNAP50 by co-immunoprecipitation but does not interact with SNAP45 or TBP. Antibody depletion of SNAPc from nuclear extracts, in vitro transcription, co-immunoprecipitation The EMBO journal High 9003788
1996 SNAP45 interacts with TBP and is required for both RNA polymerase II and III snRNA gene transcription; this established that SNAPC1 (SNAP43) resides in a complex that also contains TBP-interacting subunit SNAP45. Co-immunoprecipitation, electrophoretic mobility shift assay with antibody supershift, in vitro transcription Proceedings of the National Academy of Sciences of the United States of America Medium 8633057
1998 Recombinant SNAPc was reconstituted from five subunits (SNAP43, SNAP45, SNAP50, SNAP190, and the newly identified SNAP19), confirming that this defined complex binds specifically to the PSE and directs both RNA polymerase II and III snRNA gene transcription. Recombinant protein reconstitution, PSE binding assay, in vitro transcription Genes & development High 9732265
1998 The genomic structure of the human PTFgamma/SNAP43 gene was determined: it spans ~29 kb, contains 9 exons and 8 introns, and maps to chromosome 14q22 by FISH. The gene lacks a TATA box but has Sp1, Oct1, NF1, AP1, E2F, and USF binding sites in its promoter, and has a VNTR in its 5'-UTR. Genomic cloning, primer extension, fluorescence in situ hybridization (FISH) Journal of biochemistry Medium 9644240
2000 A detailed map of subunit-subunit contacts within SNAPc was defined: SNAPC1 (SNAP43) contacts were mapped to specific domains, and complexes retaining only the interaction domains bound specifically to the PSE, establishing the minimal architecture for PSE recognition. Co-immunoprecipitation, deletion mapping, PSE binding assay (EMSA) 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. A 50-amino-acid region within SNAP190 is required for cooperative binding with TBP in the context of mini-SNAPc. Derivatives of mini-SNAPc lacking this region are still transcriptionally active. Recombinant protein reconstitution, PSE/TATA promoter binding assay, in vitro transcription Molecular and cellular biology High 12391172
2003 SNAPC1 (SNAP43) directly interacts with the TBP DNA binding domain, contributing to TBP recruitment to the U6 TATA box. This interaction, along with that of SNAP190, helps assemble a RNA polymerase III-specific preinitiation complex. TBP recruitment assay, direct protein-protein interaction assay, reconstituted mini-SNAPc (SNAP43 + SNAP50 + truncated SNAP190) The Journal of biological chemistry Medium 12621023
2004 The Drosophila ortholog of SNAPC1 (SNAP43), DmPBP45, shows conformationally distinct DNA cross-linking patterns when bound to U1 versus U6 PSEs — cross-linking strongly for two helical turns downstream of U1 PSE but only half a turn downstream of U6 PSE. This conformational difference is consistent with a model where PBP conformation determines which RNA polymerase is recruited. Photo-cross-linking, S2 cell expression, functional PSE-binding assay Molecular and cellular biology Medium 14966271
2006 SNAP43 participates in direct DNA contacts during PSE recognition by SNAPc. A partial recombinant SNAPc containing SNAP190 (1-505), SNAP50, SNAP43, and SNAP19 expressed in E. coli binds DNA specifically, recruits TBP to U6 promoter DNA, and supports transcription of human U1 and U6 snRNA genes by RNA polymerases II and III. E. coli co-expression system, PSE DNA binding assay, TBP recruitment assay, reconstituted in vitro transcription Protein expression and purification Medium 16603380
2012 SNAPC1 occupies not only snRNA gene loci but also a large number of transcriptionally active protein-coding genes genome-wide, mirroring elongating RNA polymerase II across gene bodies and 3' ends. Inhibition of transcriptional elongation causes loss of SNAPC1 from gene 3' ends. Depletion of SNAPC1 diminishes transcriptional responsiveness of many genes to EGF and retinoic acid stimulation, establishing SNAPC1 as a general transcriptional coactivator functioning through elongating RNAPII. ChIP-seq with anti-SNAPC1 antibodies, SNAPC1 knockdown (siRNA/shRNA), RT-qPCR/RNA-seq for EGF and RA responsiveness, transcriptional elongation inhibitor treatment Molecular and cellular biology High 22966203
2022 Cryo-EM structure of human mini-SNAPc (SNAP190 N-terminal domain, SNAP50, SNAP43) in complex with the human U6-1 PSE was determined at 3.49 Å resolution. The structure reveals how the three subunits assemble into a stable mini-SNAPc in a 'wrap-around' mode on the PSE, with three important motifs of SNAP50 mediating both major groove and minor groove recognition of PSE in coordination with the Myb domain of SNAP190. Cryo-electron microscopy structure determination, structural analysis Nature communications High 36369505
2025 SNAPC1 is SUMOylated at lysine residues K245 and K333. A SUMOylation-deficient SNAPC1 mutant (2KR) is unable to sustain basal levels of snRNA transcription. While SNAPC1 2KR can still interact with SNAPC3 and is recruited to the PSE, its interaction with SNAPC4 is impaired, indicating that SUMOylation of SNAPC1 is required for proper SNAPc complex assembly and snRNA transcription. CRISPR/dCas9-SENP1 targeted deSUMOylation, site-directed mutagenesis (K245R/K333R), inducible degron depletion system, co-immunoprecipitation (endogenous-tagged SNAPC3 and SNAPC4), ChIP for PSE recruitment, snRNA expression 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) 151 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 18 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 12 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

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