RING1

RING1 is a RING domain-containing E3 ubiquitin ligase that functions as a catalytic core subunit of Polycomb Repressive Complex 1 (PRC1), monoubiquitinating histone H2A at K119 to enforce transcriptional silencing of developmental genes, including maintaining poised RNA Polymerase II at bivalent loci in embryonic stem cells (PMID:18037880, PMID:29386386). RING1 assembles into PcG complexes through direct interactions with BMI1, HPC/Polycomb homologs, and YY1, and its PRC1-mediated repression of BMP/Wnt ligand genes and Meis2 is essential for proper ventral telencephalon patterning and limb proximal-distal specification (PMID:9199346, PMID:33177537, PMID:26674308). Beyond chromatin, RING1 ubiquitinates non-histone substrates: it promotes p53 proteasomal degradation independently of PRC1, and catalyzes K48-linked ubiquitination of GSDMD at K51/K168 to suppress pyroptosis (PMID:29187402, PMID:40369166). A de novo RING1 missense mutation (p.R95Q) that selectively ablates nucleosomal H2A monoubiquitination causes neurodevelopmental defects including impaired neuronal migration and delayed DNA damage repair in neural progenitor cells (PMID:29386386, PMID:39256363).

1. 1997 High

   Establishing that RING1 is a Polycomb group protein: RING1 was shown to physically interact with multiple PcG proteins and function as a transcriptional repressor, placing it within the PcG silencing machinery.

   Evidence Yeast two-hybrid, co-immunoprecipitation, colocalization, and reporter repression in mammalian cells

   PMID:9199346

   Open questions at the time

   • Enzymatic activity of RING1 not yet identified
   • Mechanism of transcriptional repression unknown
2. 1999 High

   Defining the modular architecture of RING1 interactions: self-association and BMI1 binding occur through separable domains, and overexpression demonstrated oncogenic potential via deregulation of PcG targets.

   Evidence Directed yeast two-hybrid, in vitro binding, soft-agar colony assay, and xenograft tumor formation

   PMID:9858531

   Open questions at the time

   • Oncogenic mechanism not linked to specific enzymatic activity
   • Whether RING1 transformation depends on PcG complex integrity unknown
3. 2004 High

   Expanding RING1's interactome beyond PcG: RING1 was found to bridge into Notch signaling by interacting with KyoT2 and suppressing RBP-J-mediated transactivation, while cross-species rescue confirmed deep evolutionary conservation of RING1 function.

   Evidence Yeast two-hybrid, GST pulldown, co-IP, reporter assays (KyoT2 study); genetic rescue of Drosophila Ring/Sce mutants with murine Ring1

   PMID:14999091 PMID:15147763

   Open questions at the time

   • Physiological relevance of RING1-KyoT2-RBP-J complex in development not established
   • Whether Notch crosstalk depends on RING1 catalytic activity unknown
4. 2006 Medium

   Genetic evidence linked RING1 and YY1 in maintaining axial skeletal patterning, establishing that RING1-containing PcG complexes coordinate with sequence-specific DNA-binding factors in vivo.

   Evidence Double-mutant mice (Ring1/YY1 epistasis) and GST pulldown

   PMID:16624538

   Open questions at the time

   • Direct target genes mediating the skeletal phenotype not identified
   • Whether RING1-YY1 interaction is direct or mediated by other PcG components unclear
5. 2007 High

   The key catalytic function of RING1 was identified: monoubiquitination of H2A at K119, which enforces a poised RNA Pol II state at bivalent developmental genes in ES cells, providing the mechanistic basis for PRC1-mediated gene silencing.

   Evidence Conditional Ring1A/Ring1B knockout in mouse ES cells with ChIP for H2Aub, RNAP phospho-CTD, and transcriptional profiling

   PMID:18037880

   Open questions at the time

   • Relative contributions of Ring1A vs Ring1B to H2Aub at specific loci not fully resolved
   • Mechanism by which H2Aub restrains Pol II elongation not defined
6. 2015 High

   RING1-mediated PRC1 repression was shown to be essential for limb development: Ring1A/B directly repress Meis2 in distal forelimb, and genetic removal of Meis2 partially rescues limb defects, establishing an epistatic developmental circuit.

   Evidence Conditional Ring1A/B knockout and Ring1A/B/Meis2 triple mutant mice with limb morphological and gene expression analysis

   PMID:26674308

   Open questions at the time

   • Additional PRC1 target genes contributing to limb patterning not comprehensively mapped
   • Whether RING1 catalytic activity versus scaffolding drives the phenotype unresolved
7. 2017 High

   RING1 was discovered to ubiquitinate p53 independently of PRC1, promoting its proteasomal degradation and revealing a non-chromatin oncogenic mechanism distinct from its epigenetic silencing role.

   Evidence In vitro ubiquitination assay with RING domain mutagenesis, siRNA knockdown with cell cycle/apoptosis readouts

   PMID:29187402

   Open questions at the time

   • Ubiquitin chain type on p53 not specified
   • In vivo relevance for tumorigenesis not tested with genetic models
8. 2018 High

   A patient-derived RING1 missense mutation (R95Q) revealed separation of function: the mutant retains general ubiquitin chain-forming activity but cannot monoubiquitinate H2A on nucleosomes, causing neurodevelopmental defects and establishing RING1 as a disease gene for neurodevelopmental disorder.

   Evidence In vitro nucleosome ubiquitination assay, patient cell H2AK119ub1 immunoblotting, CRISPR knock-in of ortholog in C. elegans with neuronal phenotyping

   PMID:29386386

   Open questions at the time

   • Structural basis for substrate-specific catalytic defect not determined
   • Full clinical spectrum of RING1 mutations unknown
9. 2020 High

   Ring1b-mediated PRC1 silencing was shown to control ventral telencephalon patterning by directly repressing BMP and Wnt ligand loci, permitting Shh expression and ventral identity.

   Evidence Conditional Ring1A/B deletion in neuroepithelium, ChIP for Ring1B and H3K27me3 at BMP/Wnt loci, forced BMP/Wnt activation experiments

   PMID:33177537

   Open questions at the time

   • Whether Ring1a alone suffices for any ventral telencephalon patterning not tested
   • Downstream chromatin remodeling events at derepressed loci not characterized
10. 2024 High

    Hypomorphic RING1 variants were shown to act dominantly by occupying target chromatin without catalyzing ubiquitination, thereby blocking access of functional PRC1 and impairing DNA damage repair and cell cycle progression in neural progenitors.

    Evidence ChIP-seq for H2AK119ub1, DNA damage repair assays, cell cycle analysis, and transcriptomics in human iPSC-derived NPCs with RING1 hypomorphic alleles

    PMID:39256363

    Open questions at the time

    • Specific DNA repair pathway(s) dependent on H2AK119ub1 not identified
    • Whether dominant-negative mechanism applies in non-neural tissues unknown
11. 2025 High

    RING1 was found to catalyze K48-linked ubiquitination of GSDMD at specific lysines (K51, K168), promoting proteasomal degradation of GSDMD and suppressing pyroptosis during bacterial infection — a function entirely outside the chromatin/PcG paradigm.

    Evidence Co-IP, in vitro ubiquitination with GSDMD lysine mutagenesis, Ring1 KO mouse infection models, E3 ligase inhibitor PRT4165

    PMID:40369166

    Open questions at the time

    • How RING1 is recruited to GSDMD upon inflammasome activation not defined
    • Whether RING1 ubiquitinates other inflammasome components unknown

• Major unresolved questions include the structural basis for RING1's substrate selectivity between nucleosomal H2A, p53, and GSDMD, the mechanisms governing RING1 recruitment to non-chromatin substrates, and the full spectrum of human disease caused by RING1 variants.
• No crystal structure of RING1 with nucleosome or non-histone substrate
• Relative in vivo contribution of RING1 vs RNF2 at most genomic loci unresolved
• Comprehensive genotype-phenotype correlation for RING1 mutations lacking