interchromatin granule

GO:0035061 · Ribonucleoprotein · Other · Proposed

A class of nuclear body measuring 20-25 nm in diameter and distributed throughout the interchromatin space, linked together by thin fibrils. They are believed to be storage centers for various snRNAs, snRNPs, serine/arginine-rich proteins and RNA polymerase II. A typical mammalian cell contains 25-50 clusters of interchromatin granules. Interchromatin granule clusters do not contain the heterogeneous nuclear RNA-binding proteins (hnRNPs). [GO:0035061]

Synonyms: ICG

Part of: nuclear lumen (GO:0031981)

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
SR splicing factor cohort	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	SRSF2, SRSF6		UNKNOWN	Serine/arginine-rich pre-mRNA splicing factors that concentrate in interchromatin granule clusters. `GO:0035061` GO:0035061 describes interchromatin granules as storage centers for serine/arginine-rich proteins. `DOI:10.1242/jcs.113.19.3485` Prasanth et al. 2000 used SC35 and SRp55 as markers of SR-protein nuclear speckles that were distinct from hnRNP-containing omega speckles.
spliceosomal snRNP complex	Protein complex	part of	`GO:0097525`			UNKNOWN	Spliceosomal small nuclear ribonucleoprotein complexes enriched in interchromatin granule clusters. `GO:0035061` GO:0035061 describes interchromatin granules as storage centers for snRNAs and snRNPs. `DOI:10.1093/emboj/18.15.4308` Mintz et al. 1999 biochemically purified interchromatin granule clusters and identified many proteins linked to pre-mRNA splicing.

Taxonomic distribution

NCBITaxon:10090 Mus musculus — VARIABLE: Interchromatin granule clusters were purified and proteomically characterized from mouse liver nuclei as nuclear fractions enriched for pre-mRNA processing factors. [DOI:10.1091/mbc.e04-03-0253]

Canonical examples

NCBITaxon:10090 Mus musculus — Mouse liver nuclei were used to purify interchromatin granule clusters and identify a protein composition dominated by pre-mRNA splicing and processing factors. [DOI:10.1091/mbc.e04-03-0253]

Functions

pre-mRNA processing factor reservoir — Interchromatin granule clusters concentrate pre-mRNA splicing and RNA-processing factors in mammalian nuclear bodies proposed to serve as assembly, modification and/or storage sites for pre-mRNA processing machinery.
- DOI:10.1091/mbc.e04-03-0253 Saitoh et al. 2004 found that most identified IGC proteins were associated with RNA metabolism and that pre-mRNA splicing proteins predominated.

Mechanism graphs

IGCs concentrate pre-mRNA processing factors (FUNCTION)

Interchromatin granule clusters are nuclear RNP granules that concentrate SR splicing factors and spliceosomal snRNPs while remaining distinct from hnRNP-containing omega speckles.

Subject	Predicate	Object	Evidence
SR splicing factor cohort	localizes to	interchromatin granule	`DOI:10.1242/jcs.113.19.3485` Prasanth et al. 2000 used SC35 and SRp55 SR-protein nuclear speckles as interchromatin-granule markers.
spliceosomal snRNP complex	are enriched in	interchromatin granule	`GO:0035061` GO:0035061 describes interchromatin granules as storage centers for snRNAs and snRNPs.
interchromatin granule	supports	pre-mRNA processing factor reservoir	`DOI:10.1091/mbc.e04-03-0253` Saitoh et al. 2004 found that 54% of identified IGC proteins had known pre-mRNA-splicing functions and that 81% were associated with RNA metabolism.
interchromatin granule	is distinct from	omega speckle	`DOI:10.1242/jcs.113.19.3485` Prasanth et al. 2000 reported that SC35 and SRp55 SR-protein nuclear speckles did not colocalize with omega speckles.

Discussions

CURATION_TODO (OPEN): Resolve the exact snRNA, snRNP, SR-protein and RNA polymerase II constituent boundaries for interchromatin granules. This first GO:0035061 record captures the GO term, SR splicing factors and spliceosomal snRNPs while leaving the purified mammalian IGC proteome, individual snRNAs, RNA polymerase II storage claims and species-to-species variation to a later pass.

Evidence

GO:0035061 Gene Ontology cellular-component term for interchromatin granule and the exact ICG synonym.
GO:0016604 Gene Ontology cellular-component parent term for nuclear body.
GO:0140168 Gene Ontology cellular-component ancestor term for nuclear ribonucleoprotein granule.
GO:0031981 Gene Ontology cellular-component term for the nuclear lumen.
GO:0097525 Gene Ontology cellular-component term for spliceosomal snRNP complex.
DOI:10.1093/emboj/18.15.4308 Mintz, Patterson, Neuwald, Spahr and Spector 1999, Purification and biochemical characterization of interchromatin granule clusters, EMBO Journal.
DOI:10.1091/mbc.e04-03-0253 Saitoh et al. 2004, Proteomic analysis of interchromatin granule clusters, Molecular Biology of the Cell.
DOI:10.1242/jcs.113.19.3485 Prasanth, Rajendra, Lal and Lakhotia 2000 distinguished Drosophila omega speckles from SC35- and SRp55-containing SR-protein interchromatin granules.

Curation history

2026-09-28T07:05:27Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-28T07:07:08Z codex · EXPANDED_RECORD — Added GO ICG synonymy, nuclear-body and nuclear-RNP-granule parentage, nuclear-lumen parthood, SR splicing factor and spliceosomal snRNP components, Mus musculus IGC proteomics scope, pre-mRNA processing reservoir evidence, a nonmechanistic splicing-factor IGC graph and an IGC-inventory TODO.
2026-09-28T07:28:30Z codex · RESOLVED_REVIEW — Resolved #1709 by narrowing the Mus musculus interchromatin-granule taxonomic-distribution row from COMMON to VARIABLE because the mouse liver IGC purification evidence establishes an observed canonical example, not species-wide commonness.

Source: data/structures/ribonucleoprotein/interchromatin_granule.yaml