U12 snRNP

GO:0005693 · Ribonucleoprotein · Ribonucleoprotein complex · Proposed

A ribonucleoprotein complex that contains small nuclear RNA U12, a heptameric ring of Sm proteins, as well as several proteins that are unique to the U12 snRNP, most of which remain associated with the U12 snRNA both while the U12 snRNP is free or assembled into a series of spliceosomal complexes. [GO:0005693]

Synonyms: snRNP U12

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Components

Component	Type	Part of / acts on	Grounding	Genes	Stoichiometry	Essential	Role
U12 snRNA	Rna	part of	`SO:0000399`				U12 small nuclear RNA constituent named in the U12 snRNP definition and grounded to the U12 snRNA Sequence Ontology term. `GO:0005693` GO:0005693 defines the U12 snRNP as containing small nuclear RNA U12. `SO:0000399` SO:0000399 is the Sequence Ontology term for U12 snRNA.
Sm protein ring	Protein complex	part of	Reviewed label only (reviewed name; no accession asserted)				Heptameric Sm protein-ring constituent named in the U12 snRNP definition. `GO:0005693` GO:0005693 defines the U12 snRNP as containing a heptameric ring of Sm proteins.

Taxonomic distribution

NCBITaxon:9606 Homo sapiens — COMMON: The U12 snRNP subcomplex is represented in human 18S U11/U12 snRNPs affinity purified and analyzed by mass spectrometry by Will, Schneider, Hossbach and colleagues; broader eukaryotic distribution is left for follow-up curation. [DOI:10.1261/rna.7320604]

Canonical examples

NCBITaxon:9606 Homo sapiens — Human minor-spliceosome U12 snRNP represented inside affinity-purified 18S U11/U12 snRNPs in the Will, Schneider and Hossbach composition study. [DOI:10.1261/rna.7320604]

Mechanism graphs

U12 snRNA and the Sm ring are U12 snRNP constituents (ASSEMBLY)

The U12 snRNP contains U12 small nuclear RNA and a heptameric Sm protein ring; GO:0005693 also states that additional U12-specific proteins are present, with exact family boundaries still to be resolved.

Subject	Predicate	Object	Evidence
U12 snRNA	contributes constituents to	U12 snRNP	`GO:0005693` GO:0005693 defines the U12 snRNP as containing small nuclear RNA U12.
Sm protein ring	contributes constituents to	U12 snRNP	`GO:0005693` GO:0005693 defines the U12 snRNP as containing a heptameric ring of Sm proteins.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral groundings for the Sm ring and U12-specific protein families that form the U12 snRNP. The first GO:0005693 record captures U12 snRNA and the GO-defined Sm ring at coarse granularity. Individual spliceosomal Sm proteins and U12-specific protein-family boundaries should be resolved before splitting this inventory.

Evidence

GO:0005693 Gene Ontology cellular-component term for the U12 snRNP and its exact synonym.
GO:0097525 Gene Ontology cellular-component parent term for spliceosomal snRNP complex.
SO:0000399 Sequence Ontology term for U12 snRNA.
DOI:10.1261/rna.7320604 Will, Schneider, Hossbach and colleagues 2004 affinity purified human 18S U11/U12 snRNPs and identified their protein components by mass spectrometry.
DOI:10.1515/BC.2005.084 Will and Luehrmann 2005, Splicing of a rare class of introns by the U12-dependent spliceosome, Biological Chemistry.

Curation history

2026-09-24T22:08:42Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-24T22:11:08Z codex · EXPANDED_RECORD — Added the GO exact synonym, spliceosomal snRNP parentage, U12 snRNA and Sm-ring components, human Will/Schneider/Hossbach 18S U11/U12 snRNP evidence, a minimal U12 snRNP constituent graph and a protein-component grounding TODO.
2026-09-24T22:21:10Z codex · ADDRESS_REVIEW — #1529: removed SO:0000399 from the protein-component TODO evidence because the SO U12 snRNA term does not support Sm-ring or U12-specific protein-family boundary curation.

Source: data/structures/ribonucleoprotein/u12_snrnp.yaml