precatalytic spliceosome

GO:0071011 · Ribonucleoprotein · Ribonucleoprotein complex · Proposed

A spliceosomal complex that is formed by the recruitment of a preassembled U5-containing tri-snRNP to the prespliceosome. Although all 5 snRNPs are present, the precatalytic spliceosome is catalytically inactive. The precatalytic spliceosome includes many proteins in addition to those found in the associated snRNPs. [GO:0071011]

Synonyms: mammalian spliceosomal complex B; mammalian spliceosomal complex B1; yeast spliceosomal complex A2-1

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
U5-containing tri-snRNP	Protein complex	part of	Reviewed label only (reviewed name; no accession asserted)				Preassembled, subtype-specific U5-containing tri-snRNP subcomplex recruited to the prespliceosome to form a precatalytic spliceosome. `GO:0071011` GO:0071011 defines the precatalytic spliceosome as formed by recruitment of a preassembled U5-containing tri-snRNP to the prespliceosome. `GO:0071005` GO:0071005 defines the U2-type precatalytic spliceosome by recruitment of preassembled U4/U6.U5 tri-snRNP. `GO:0071016` GO:0071016 defines the U12-type precatalytic spliceosome by recruitment of preassembled U4atac/U6atac.U5 tri-snRNP.

Mechanism graphs

U5-containing tri-snRNP recruitment forms precatalytic spliceosomes (ASSEMBLY)

Precatalytic spliceosomes form when preassembled U5-containing tri-snRNPs are recruited to prespliceosomes.

Subject	Predicate	Object	Evidence
U5-containing tri-snRNP	is recruited to form	precatalytic spliceosome	`GO:0071011` GO:0071011 defines the precatalytic spliceosome as formed by U5-containing tri-snRNP recruitment.
prespliceosome	receives	U5-containing tri-snRNP	`GO:0071011` GO:0071011 defines the precatalytic spliceosome as formed by recruiting a preassembled U5-containing tri-snRNP to the prespliceosome.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral snRNP membership and additional protein boundaries for each precatalytic spliceosome subtype. The first GO:0071011 parent record captures only the generic U5-containing tri-snRNP recruitment event supported by GO. Child records for U2-type and U12-type precatalytic spliceosomes should carry the exact U1/U2 and U4/U6.U5 or U11/U12 and U4atac/U6atac.U5 constituent boundaries that apply to those specific states.

Evidence

GO:0071011 Gene Ontology cellular-component term for precatalytic spliceosome and its GO synonyms.
GO:0005681 Gene Ontology cellular-component parent term for spliceosomal complex.
GO:0071010 Gene Ontology cellular-component term for the preceding prespliceosome state.
GO:0071005 Gene Ontology cellular-component term for the U2-type precatalytic spliceosome child state.
GO:0071016 Gene Ontology cellular-component term for the U12-type precatalytic spliceosome child state.
GO:0046540 Gene Ontology cellular-component term for the U4/U6 x U5 tri-snRNP complex.
GO:0071009 Gene Ontology cellular-component term for the U4atac/U6atac x U5 tri-snRNP complex.

Curation history

2026-09-25T08:15:45Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-25T08:16:24Z codex · EXPANDED_RECORD — Added GO narrow synonyms, spliceosomal-complex parentage, a reviewed-label-only U5-containing tri-snRNP component, a conservative tri-snRNP recruitment graph and a TODO for exact U2-type and U12-type precatalytic spliceosome boundaries.

Source: data/structures/ribonucleoprotein/precatalytic_spliceosome.yaml