SNW1

SNW1 (SKIP/NCoA-62; yeast Prp45) is a dual-function nuclear protein that couples pre-mRNA splicing to transcriptional regulation (PMID:25257309, PMID:11514567). As an essential spliceosome subunit, it associates directly with the core splicing machinery EFTUD2 (Snu114) and SNRNP200 (Brr2) through defined interaction surfaces (PMID:25450007), makes dynamic contacts with nucleotides flanking the pre-mRNA branch site during catalytic activation (PMID:26393790), and is required for early cotranscriptional recruitment of U2 and U5 snRNPs and the NTC, downstream of U1 recognition (PMID:28701519). Through this activity SNW1 enables splicing of specific introns in sororin and APC2 needed for sister chromatid cohesion and APC/C activity, with intron-less cDNA expression of these substrates rescuing cohesion defects in SNW1-depleted cells (PMID:25257309). In its transcriptional role, SNW1 acts as a coactivator that contacts the vitamin D receptor at an AF-2-independent surface of helix H10 and cooperates with SRC coactivators in a ternary complex with the VDR-RXR heterodimer to synergistically drive ligand-dependent transcription (PMID:11514567, PMID:12529369). SNW1 also detaches from the spliceosome to bind the NF-κB heterodimer and the elongation factor p-TEFb, driving transcriptional elongation of inflammatory target genes such as IL-8 and TNF (PMID:30397075), an activity negatively regulated by OGT-mediated O-GlcNAcylation of SNW1 (PMID:35818332). Developmentally, SNW1 is required for neural crest specification by setting a BMP-activity domain at the neural plate border upstream of BMP receptors (PMID:21358802), and patient mutations that impair SNW1 contacts with core spliceosomal proteins cause exon-skipping defects and reduced neural stem cell proliferation in cerebral organoids and Drosophila (PMID:40608414). A C-terminal region of the protein additionally stabilizes the Lge1 scaffold of the Bre1 H2B ubiquitin ligase, linking SNW1 to histone H2B ubiquitination (PMID:40667372).

1. 1998 Medium

   Established SNW1's first molecular role by showing it binds the vitamin D receptor and acts as a ligand-specific transcriptional coactivator, defining it as more than a generic factor.

   Evidence Yeast two-hybrid, GST pull-down, and reporter assays with VDR; parallel two-hybrid with the Ski oncoprotein and nuclear localization

   PMID:9569025 PMID:9632709

   Open questions at the time

   • Did not resolve the VDR interaction interface
   • No structural model of the coactivator contact
   • Functional role in splicing not yet recognized
2. 2001 High

   Defined how SNW1 cooperates with other coactivators, showing it engages a VDR surface distinct from SRC proteins to synergistically enhance nuclear-receptor transcription.

   Evidence Ternary complex binding, LXXLL peptide competition, co-IP, and reporter assays; later mapped to VDR helix H10 by point-mutant pull-downs

   PMID:11514567 PMID:12529369

   Open questions at the time

   • AF-2-independent interface mapped functionally but not structurally
   • Generalization beyond VDR to other nuclear receptors not established
3. 2002 Medium

   Connected SNW1 to conserved developmental signaling and splicing through model organisms, establishing both Notch-pathway requirement and an essential N-terminal SNW domain.

   Evidence Drosophila Bx42 RNAi with Notch genetic epistasis and target-gene readouts; yeast Prp45 domain complementation, GFP speckle localization, and Gal4-fusion reporter

   PMID:12204255 PMID:12359070

   Open questions at the time

   • Whether Notch effect is direct or via splicing not resolved
   • Molecular function of the SNW domain undefined
4. 2004 Medium

   Demonstrated functional conservation of the splicing role by showing human SKIP rescues lethality of the yeast Prp45 deletion.

   Evidence Genetic complementation of prp45Δ yeast with human SKIP

   PMID:15194481

   Open questions at the time

   • Complementation shows conserved function but not mechanistic detail
   • Substrate specificity in human cells not addressed
5. 2009 Medium

   Began to localize SNW1's action within the spliceosome by linking yeast Prp45 to the second-step helicase Prp22 and to splicing efficiency of non-consensus substrates.

   Evidence Synthetic lethality screen, Cwc2-pulldown complex purification, and in vivo splicing reporters with splice-site mutants

   PMID:19016306

   Open questions at the time

   • Direct vs indirect Prp22 interaction not fully resolved
   • Human relevance of the Prp22 link untested
6. 2011 High

   Placed SNW1 in vertebrate development by showing it patterns a BMP-activity domain upstream of BMP receptors to specify neural crest.

   Evidence Morpholino knockdown in Xenopus and zebrafish, pSmad1 immunostaining, BMP reporter transgenics, and rescue by targeted BMP overexpression

   PMID:21358802

   Open questions at the time

   • Whether BMP regulation is via splicing of pathway components unknown
   • Direct molecular target within the BMP axis not identified
7. 2014 High

   Resolved how SNW1 connects splicing to mitosis, identifying sororin and APC2 introns as critical substrates whose mis-splicing explains cohesion defects, and mapping direct contacts to EFTUD2 and SNRNP200.

   Evidence siRNA knockdown with RNA-seq splicing analysis, live-cell cohesion imaging, intron-less cDNA rescue; proteomics and reciprocal domain-mapped co-IP

   PMID:25257309 PMID:25450007

   Open questions at the time

   • Why specific introns depend on SNW1 not mechanistically explained
   • Structural basis of EFTUD2/SNRNP200 contacts unresolved
8. 2017 Medium

   Defined the step at which SNW1 acts in spliceosome assembly, showing yeast Prp45 contacts the branch site during catalytic activation and is needed for cotranscriptional U2/U5/NTC recruitment after U1 recognition.

   Evidence UV crosslinking of purified Bact/B*/C complexes with mass spectrometry; ChIP along gene bodies for spliceosome components with the prp45(1-169) allele

   PMID:26393790 PMID:28701519

   Open questions at the time

   • Human conservation of these assembly-stage roles not directly tested
   • How Prp45 drives the conformational coupling mechanistically unclear
9. 2019 Medium

   Revealed a regulated switch from spliceosome to transcription, with SNW1 detaching from the spliceosome to bind NF-κB and p-TEFb and drive elongation of inflammatory genes, and engaging RBPJ for Notch targets.

   Evidence Genome-wide RNAi screen, co-IP, and knockdown with target-gene expression for NF-κB; co-IP and reporter assays for RBPJ in neuroblastoma

   PMID:30397075 PMID:30642633

   Open questions at the time

   • Trigger and kinetics of the spliceosome-to-NF-κB switch undefined
   • RBPJ interaction rests on a single Co-IP without reciprocal validation
10. 2020 Low

    Extended SNW1's NF-κB role to innate antiviral signaling, showing it engages IKKγ to promote influenza-induced NF-κB and TBK1 activation.

    Evidence Co-IP, depletion/overexpression with reporter and ELISA, and western blot for pathway activation

    PMID:32805409

    Open questions at the time

    • IKKγ interaction from a single Co-IP without reciprocal confirmation
    • Direct vs indirect engagement unresolved
11. 2022 Medium

    Identified a post-translational control point, showing O-GlcNAcylation of SNW1 suppresses its NF-κB-activating function.

    Evidence IP-based detection of O-GlcNAc on SNW1, NF-κB reporter, OGT-inhibitor experiments, ELISA, and an in vivo MCAO model

    PMID:35818332

    Open questions at the time

    • Modified residue(s) on SNW1 not mapped
    • Whether O-GlcNAcylation also affects splicing function untested
12. 2024 Low

    Broadened the splicing repertoire and disease relevance, linking SNW1 to SRPK1 transcript choice via NUDT21/CPSF6 and to a chromatin complex with SF3B1, P-TEFb, and HTATSF1.

    Evidence Co-IP, knockdown, RT-PCR splicing and invasion assays for SRPK1; co-IP, fractionation and ChIP after SF3B1 inhibition (preprint); DSA target-engagement and SNW1-RXR co-IP for ALDH2

    PMID:39591904 PMID:41704767

    Open questions at the time

    • SRPK1 and ALDH2 mechanisms rest on single-lab Co-IP/rescue
    • SF3B1/P-TEFb complex evidence is a preprint with limited SNW1-specific follow-up
13. 2025 Medium

    Established a human disease link and a new C-terminal function, showing pathogenic SNW1 mutations disrupt spliceosomal contacts and exon inclusion to impair neurodevelopment, while the C-terminus stabilizes the Lge1 scaffold to promote H2B ubiquitination.

    Evidence Patient mutation analysis, mutant-vs-WT co-IP, RNA-seq, Drosophila RNAi and cerebral organoid models; truncation genetics, pulldown-MS, H2B-ubiquitination western blot and cross-species complementation (preprint)

    PMID:40608414 PMID:40667372

    Open questions at the time

    • Genotype-phenotype spectrum of SNW1 mutations not fully delineated
    • Lge1/Bre1 link demonstrated in yeast with cross-species rescue but not in human cells
    • How splicing and H2B-ubiquitination roles are coordinated unknown

• How SNW1 dynamically partitions between its spliceosomal and transcriptional/chromatin roles, and what governs substrate intron selectivity, remains unresolved.
• No structural model of SNW1 within the human spliceosome
• Signals controlling the spliceosome-to-transcription switch unknown
• Rules determining which introns require SNW1 undefined