U2-type prespliceosome

GO:0071004 · Ribonucleoprotein · Ribonucleoprotein complex · Proposed

A spliceosomal complex that is formed by association of the 5' splice site with the U1 snRNP, while the branch point sequence is recognized by the U2 snRNP. The prespliceosome includes many proteins in addition to those found in the U1 and U2 snRNPs. Commitment to a given pair of 5' and 3' splice sites occurs at the time of prespliceosome formation. [GO:0071004]

Synonyms: major prespliceosome; GT-AG prespliceosome; mammalian U2-type spliceosomal complex A; yeast U2-type spliceosomal complex B

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
U1 snRNP	Protein complex	part of	`GO:0005685`				Small nuclear ribonucleoprotein associated with the 5-prime splice site in the U2-type prespliceosome. `GO:0071004` GO:0071004 defines the U2-type prespliceosome as formed by association of the 5-prime splice site with U1 snRNP. `GO:0005685` GO:0005685 is the Gene Ontology cellular-component term for the U1 snRNP.
U2 snRNP	Protein complex	part of	`GO:0005686`				Small nuclear ribonucleoprotein that recognizes the branch point sequence in the U2-type prespliceosome. `GO:0071004` GO:0071004 defines the U2-type prespliceosome by branch-point-sequence recognition by the U2 snRNP. `GO:0005686` GO:0005686 is the Gene Ontology cellular-component term for the U2 snRNP.

Mechanism graphs

U1 and U2 snRNPs define the U2-type prespliceosome (ASSEMBLY)

The U2-type prespliceosome forms when U1 snRNP associates with the 5-prime splice site while U2 snRNP recognizes the branch-point sequence.

Subject	Predicate	Object	Evidence
U1 snRNP	associates with splice site in	U2-type prespliceosome	`GO:0071004` GO:0071004 defines this prespliceosome by 5-prime splice-site association with U1 snRNP.
U2 snRNP	recognizes branch point in	U2-type prespliceosome	`GO:0071004` GO:0071004 defines this prespliceosome by branch-point-sequence recognition by U2 snRNP.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral component boundaries for U2-type prespliceosome proteins beyond the GO-defined U1 and U2 snRNP subcomplexes. The first GO:0071004 record captures the defining U1 and U2 snRNP subcomplexes. Additional prespliceosome proteins should be resolved into exact source-neutral families or subcomplexes before expanding the component list.

Evidence

GO:0071004 Gene Ontology cellular-component term for the U2-type prespliceosome and its GO synonyms.
GO:0071010 Gene Ontology cellular-component parent term for prespliceosome.
GO:0005684 Gene Ontology cellular-component parent term for U2-type spliceosomal complex.
GO:0005685 Gene Ontology cellular-component term for the U1 snRNP.
GO:0005686 Gene Ontology cellular-component term for the U2 snRNP.

Curation history

2026-09-24T18:26:07Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-24T18:26:50Z codex · EXPANDED_RECORD — Added GO synonymy, prespliceosome and U2-type parentage, GO-grounded U1 and U2 snRNP components, a minimal snRNP assembly graph and a protein-component grounding TODO.
2026-09-24T18:37:38Z codex · ADDRESS_REVIEW — #1515: replaced narrow A-complex wording with generic prespliceosome wording.

Source: data/structures/ribonucleoprotein/u2_type_prespliceosome.yaml