U12-type precatalytic spliceosome

GO:0071016 · Ribonucleoprotein · Ribonucleoprotein complex · Proposed

A spliceosomal complex that is formed by the recruitment of the preassembled U4atac/U6atac.U5 tri-snRNP to the U12-type 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 U11, U12 and U4atac/U6atac.U5 snRNPs. [GO:0071016]

Synonyms: minor precatalytic spliceosome; AT-AC precatalytic spliceosome; mammalian U12-type spliceosomal complex B; mammalian U12-type spliceosomal complex B1; yeast U12-type 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
U11/U12 snRNP	Protein complex	part of	`GO:0034693`				Heterodimeric minor-spliceosome snRNP subcomplex present when U4atac/U6atac.U5 tri-snRNP is recruited to the U12-type prespliceosome. `GO:0071016` GO:0071016 defines the U12-type precatalytic spliceosome as containing all five minor-spliceosome snRNPs and as formed by tri-snRNP recruitment to the U12-type prespliceosome. `GO:0034693` GO:0034693 is the Gene Ontology cellular-component term for the U11/U12 snRNP. `GO:0071015` GO:0071015 defines the U12-type prespliceosome state that precedes U4atac/U6atac.U5 tri-snRNP recruitment.
U4atac/U6atac x U5 tri-snRNP complex	Protein complex	part of	`GO:0071009`				Preassembled minor-spliceosome tri-snRNP subcomplex recruited to the U12-type prespliceosome to form the U12-type precatalytic spliceosome. `GO:0071016` GO:0071016 defines the U12-type precatalytic spliceosome as formed by recruitment of preassembled U4atac/U6atac.U5 tri-snRNP to the U12-type prespliceosome. `GO:0071009` GO:0071009 is the Gene Ontology cellular-component term for the U4atac/U6atac x U5 tri-snRNP complex.

Mechanism graphs

U4atac/U6atac.U5 tri-snRNP recruitment forms the U12-type precatalytic spliceosome (ASSEMBLY)

The U12-type precatalytic spliceosome forms when preassembled U4atac/U6atac.U5 tri-snRNP joins the U11/U12-containing prespliceosome on pre-mRNA.

Subject	Predicate	Object	Evidence
U11/U12 snRNP	cooperatively binds splice signals in	U12-type prespliceosome	`GO:0071015` GO:0071015 defines the U12-type prespliceosome by U11/U12 snRNP binding to the 5-prime splice site and branch point sequence.
U4atac/U6atac x U5 tri-snRNP complex	is recruited to form	U12-type precatalytic spliceosome	`GO:0071016` GO:0071016 defines the U12-type precatalytic spliceosome as the state formed by recruitment of U4atac/U6atac.U5 tri-snRNP to the U12-type prespliceosome.
U12-type prespliceosome	receives	U4atac/U6atac x U5 tri-snRNP complex	`GO:0071016` GO:0071016 defines the U12-type precatalytic spliceosome as formed by tri-snRNP recruitment to the U12-type prespliceosome.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral component boundaries for U12-type precatalytic spliceosome proteins beyond the GO-defined U11/U12 and U4atac/U6atac.U5 snRNP subcomplexes. The first GO:0071016 record captures the defining minor-spliceosome snRNP subcomplexes. Additional U12-type precatalytic spliceosome proteins should be resolved into exact source-neutral families or subcomplexes before expanding the component list.

Evidence

GO:0071016 Gene Ontology cellular-component term for the U12-type precatalytic spliceosome and its GO synonyms.
GO:0071011 Gene Ontology cellular-component parent term for precatalytic spliceosome.
GO:0005689 Gene Ontology cellular-component parent term for U12-type spliceosomal complex.
GO:0071015 Gene Ontology cellular-component term for the U12-type prespliceosome.
GO:0034693 Gene Ontology cellular-component term for the U11/U12 snRNP.
GO:0071009 Gene Ontology cellular-component term for the U4atac/U6atac x U5 tri-snRNP complex.
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

2026-09-24T23:45:07Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-24T23:45:55Z codex · EXPANDED_RECORD — Added GO exact and narrow synonyms, precatalytic and U12-type spliceosomal-complex parentage, GO-grounded U11/U12 and U4atac/U6atac x U5 snRNP components, Will/Luehrmann U12-spliceosome evidence, a conservative tri-snRNP recruitment graph and a protein-component grounding TODO.
2026-09-24T23:55:28Z codex · ADDRESS_REVIEW — #1535: replaced the generic U11/U12 snRNP edge predicate with explicit splice-signal binding wording in the U12-type precatalytic spliceosome assembly graph.

Source: data/structures/ribonucleoprotein/u12_type_precatalytic_spliceosome.yaml