catalytic step 2 spliceosome

GO:0071013 · Ribonucleoprotein · Ribonucleoprotein complex · Proposed

A spliceosomal complex that contains three snRNPs, including U5, bound to a splicing intermediate in which the first catalytic cleavage of the 5' splice site has occurred. The precise subunit composition differs significantly from that of the catalytic step 1, or activated, spliceosome, and includes many proteins in addition to those found in the associated snRNPs. [GO:0071013]

Synonyms: mammalian spliceosomal complex C; mammalian spliceosomal complex C1; yeast spliceosomal complex A2-2

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 snRNP	Protein complex	part of	`GO:0005682`				Conserved small nuclear ribonucleoprotein bound to the splicing intermediate in catalytic step 2 spliceosomes. `GO:0071013` GO:0071013 defines the catalytic step 2 spliceosome as containing three snRNPs including U5. `GO:0005682` GO:0005682 is the Gene Ontology cellular-component term for the U5 snRNP. `GO:0071007` GO:0071007 names U5 as one of the U2-type catalytic step 2 spliceosome snRNPs. `GO:0071018` GO:0071018 names U5 as one of the U12-type catalytic step 2 spliceosome snRNPs.
catalytic step 2 subtype-specific partner snRNPs	Protein complex	part of	Reviewed label only (reviewed name; no accession asserted)				Subtype-specific pair of non-U5 snRNP constituents bound to the splicing intermediate in catalytic step 2 spliceosomes. `GO:0071013` GO:0071013 defines the catalytic step 2 spliceosome as containing three snRNPs including U5, leaving two additional subtype-specific snRNP constituents. `GO:0071007` GO:0071007 defines the U2-type catalytic step 2 spliceosome as containing U2 and U6 snRNPs alongside U5. `GO:0071018` GO:0071018 defines the U12-type catalytic step 2 spliceosome as containing U12 and U6atac snRNPs alongside U5.

Mechanism graphs

U5 and subtype-specific snRNPs bind the catalytic step 2 intermediate (ASSEMBLY)

Catalytic step 2 spliceosomes contain a conserved U5 snRNP and two subtype-specific partner snRNPs bound to a splicing intermediate after first catalytic cleavage of the 5-prime splice site.

Subject	Predicate	Object	Evidence
U5 snRNP	binds splicing intermediate in	catalytic step 2 spliceosome	`GO:0071013` GO:0071013 defines catalytic step 2 spliceosomes as including U5 bound to a splicing intermediate.
catalytic step 2 subtype-specific partner snRNPs	bind splicing intermediate in	catalytic step 2 spliceosome	`GO:0071007` GO:0071007 defines the U2-type catalytic step 2 spliceosome as containing U2, U5 and U6 snRNPs. `GO:0071018` GO:0071018 defines the U12-type catalytic step 2 spliceosome as containing U12, U5 and U6atac snRNPs.
catalytic step 1 spliceosome	is remodeled after first catalytic cleavage to form	catalytic step 2 spliceosome	`GO:0071013` GO:0071013 defines the catalytic step 2 spliceosome by the first catalytic cleavage having occurred.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral non-U5 snRNP membership and additional protein boundaries for each catalytic step 2 spliceosome subtype. The GO:0071013 parent record captures the generic presence of a conserved U5 snRNP plus two non-U5 snRNPs whose exact identities depend on the U2-type or U12-type spliceosome subtype. Child records for U2-type and U12-type catalytic step 2 spliceosomes carry the exact U2/U6 and U12/U6atac partner-snRNP boundaries that apply to those specific states.

Evidence

GO:0071013 Gene Ontology cellular-component term for catalytic step 2 spliceosome and its GO synonyms.
GO:0005681 Gene Ontology cellular-component parent term for spliceosomal complex.
GO:1902494 Gene Ontology cellular-component parent term for catalytic complex.
GO:0071012 Gene Ontology cellular-component term for the preceding catalytic step 1 spliceosome state.
GO:0071007 Gene Ontology cellular-component term for the U2-type catalytic step 2 spliceosome child state.
GO:0071018 Gene Ontology cellular-component term for the U12-type catalytic step 2 spliceosome child state.
GO:0005682 Gene Ontology cellular-component term for the U5 snRNP.
GO:0005686 Gene Ontology cellular-component term for the U2 snRNP.
GO:0005688 Gene Ontology cellular-component term for the U6 snRNP.
GO:0005693 Gene Ontology cellular-component term for the U12 snRNP.
GO:0005691 Gene Ontology cellular-component term for the U6atac snRNP.

Curation history

2026-09-25T09:16:08Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-25T09:17:21Z codex · EXPANDED_RECORD — Added GO narrow synonyms, spliceosomal and catalytic-complex parentage, a reviewed-label-only catalytic step 2 splicing-intermediate-bound snRNP component, a conservative post-first-cleavage graph and a TODO for exact U2-type and U12-type catalytic step 2 spliceosome boundaries.
2026-09-25T09:28:02Z codex · ADDRESS_REVIEW — #1565: split invariant U5 snRNP into a GO-grounded constituent and narrowed the reviewed-label-only component to the two subtype-specific partner snRNPs.

Source: data/structures/ribonucleoprotein/catalytic_step_2_spliceosome.yaml