28OE

Human PRC1.4 in complex with native UBCH5C bound to a H3Kc27me3 mononucleosome

Summary for 28OE

• Entry DOI: 10.2210/pdb28oe/pdb
• EMDB information: 56669 56717
• Descriptor: Isoform 2 of Polyhomeotic-like protein 2, DNA (151-MER), ZINC ION, ... (12 entities in total)
• Functional Keywords: prc1, prc1.4, nucleosome, ubch5c, gene regulation, h3kc27me3
• Biological source: Homo sapiens (human); More
• Total number of polymer chains: 15
• Total formula weight: 408773.75

Authors

Ciapponi, M.,Mueller, J. (deposition date: 2026-02-10, release date: 2026-09-16, Last modification date: 2026-09-23)

Primary citation

Ciapponi, M.,Cafiso, M.,Schkolziger, S.,Benda, C.,Bonnet, J.,Muller, J.
Cryo-EM structure, enzymatic activity and genome targeting of canonical PRC1.
Nat.Struct.Mol.Biol., 2026

PubMed Abstract: Canonical Polycomb repressive complex 1 (cPRC1) preserves cell fate decisions by repressing aberrant transcription of developmental regulator genes. We report the cryo-electron microscopy structure of the human cPRC1 holocomplex assembled from RING1B, BMI1, PHC2 and CBX7 bound to an H3K27me3-modified mononucleosome together with the ubiquitin-conjugating enzyme UBCH5C. cPRC1 adopts a compact, highly integrated architecture in which the subunits RING1B, BMI1 and PHC2 form an extended interface that positions UBCH5C on the nucleosome to enable efficient monoubiquitination of histone H2A at K119. This organization is conserved in Drosophila, where mutational analyses identify the PHC2 ortholog Polyhomeotic (Ph) as a central scaffold and targeting factor. The Ph HD domain is required for complex assembly, whereas the Ph SAM domain is dispensable for assembly but essential for cPRC1 recruitment to Polycomb target genes and productive H2A monoubiquitination at these loci.

PubMed: 42736418
DOI: 10.1038/s41594-026-01885-6

Experimental method

ELECTRON MICROSCOPY (2.74 Å)