nucleolus

GO:0005730 · Other · Other · Proposed

A dense, non-membrane-bounded body in the eukaryotic nuclear lumen that concentrates ribosomal DNA transcription, pre-rRNA processing, and early ribosomal subunit assembly. [GO:0005730]

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	Essential	Role
nucleolar chromatin	Other	part of	`GO:0030874`	UNKNOWN	Nucleolus-associated nuclear chromatin that includes the DNA encoding ribosomal RNA. `GO:0030874` GO:0030874 defines nucleolar chromatin as nuclear chromatin associated with the nucleolus, including DNA that encodes rRNA.
RNA polymerase I complex	Protein complex	part of	`GO:0005736`	UNKNOWN	Nucleolar polymerase complex that transcribes ribosomal DNA to produce the large pre-rRNA precursor. `GO:0005736` GO:0005736 identifies RNA polymerase I as a eukaryotic nuclear complex that typically produces rRNAs. `DOI:10.1146/annurev.genet.33.1.261` Venema and Tollervey 1999 review RNA polymerase I transcription during Saccharomyces cerevisiae ribosome synthesis.
small-subunit processome	Other	part of	`GO:0032040`	UNKNOWN	Early preribosomal ribonucleoprotein complex that contains 35S pre-rRNA and U3 snoRNA in budding yeast. `GO:0032040` GO:0032040 defines the small-subunit processome as a large early preribosomal ribonucleoprotein complex. `DOI:10.1038/nature00769` Dragon et al. 2002 characterized a large nucleolar U3 ribonucleoprotein required for 18S rRNA biogenesis.
box H/ACA snoRNP complex	Other	part of	`GO:0031429`	UNKNOWN	Small nucleolar ribonucleoprotein complex that guides pseudouridylation of rRNA during ribosome synthesis. `GO:0031429` GO:0031429 defines the box H/ACA snoRNP complex as a nucleolar complex that catalyzes pseudouridylation of rRNA residues.

Taxonomic distribution

NCBITaxon:2759 Eukaryota — COMMON: Nucleoli are non-membrane-bounded bodies of eukaryotic nuclei that concentrate ribosomal gene transcription and early ribosome biogenesis. [GO:0005730]

Canonical examples

NCBITaxon:4932 Saccharomyces cerevisiae — Budding-yeast model in which nucleolar ribosome synthesis includes 35S pre-rRNA processing and U3-containing small-subunit processome assembly. [DOI:10.1038/nature00769]

Functions

transcription by RNA polymerase I GO:0006360 — RNA polymerase I in the nucleolus transcribes ribosomal DNA to produce the major pre-rRNA precursor.
- GO:0006360 GO:0006360 denotes RNA synthesis from a DNA template by RNA polymerase I.
- DOI:10.1146/annurev.genet.33.1.261 Venema and Tollervey 1999 review rDNA transcription as the first stage of yeast ribosome synthesis.
rRNA processing GO:0006364 — Nucleolar ribonucleoproteins process primary rRNA transcripts as part of ribosome biogenesis.
- GO:0006364 GO:0006364 denotes conversion of a primary rRNA transcript into mature rRNA molecules.
- DOI:10.1038/nature00769 Dragon et al. 2002 identified the nucleolar U3 small-subunit processome as required for 18S rRNA biogenesis.
ribosome biogenesis GO:0042254 — The nucleolus organizes early transcription, rRNA processing, and preribosomal assembly steps that contribute to production of cytoplasmic ribosomal subunits.
- GO:0042254 GO:0042254 denotes the biosynthesis, assembly, and arrangement of ribosome-subunit constituents.
- DOI:10.1038/nrm2184 Boisvert et al. 2007 review the nucleolus as a eukaryotic nuclear body centered on ribosome biogenesis.

Mechanism graphs

Nucleolar RNPs support ribosome biogenesis (FUNCTION)

In the Saccharomyces cerevisiae nucleolus, RNA polymerase I transcribes rDNA within nucleolar chromatin while snoRNP-containing preribosomal complexes process pre-rRNA during early ribosome biogenesis.

Subject	Predicate	Object	Evidence
RNA polymerase I complex	transcribes rDNA within	nucleolar chromatin	`GO:0006360` GO:0006360 covers RNA polymerase I transcription from DNA templates. `DOI:10.1146/annurev.genet.33.1.261` Venema and Tollervey 1999 review RNA polymerase I transcription of ribosomal DNA in Saccharomyces ribosome synthesis.
RNA polymerase I complex	produces	pre-rRNA	`DOI:10.1146/annurev.genet.33.1.261` Venema and Tollervey 1999 review pre-rRNA production during budding-yeast ribosome synthesis.
small-subunit processome	processes	pre-rRNA	`GO:0032040` GO:0032040 defines the small-subunit processome as an early preribosomal complex that includes the 35S pre-rRNA and U3 snoRNA in S. cerevisiae. `DOI:10.1038/nature00769` Dragon et al. 2002 characterized the nucleolar U3 ribonucleoprotein required for 18S rRNA biogenesis.
box H/ACA snoRNP complex	modifies	pre-rRNA	`GO:0031429` GO:0031429 defines a nucleolar H/ACA snoRNP complex that catalyzes rRNA pseudouridylation.
nucleolus	organizes	ribosome biogenesis	`DOI:10.1038/nrm2184` Boisvert et al. 2007 review the nucleolus as a major site of eukaryotic ribosome biogenesis.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral nucleolar component boundaries for the remaining pre-40S and pre-60S particles, box C/D snoRNPs, and trans-acting yeast ribosome-biogenesis factors. This first nucleolus record grounds exact GO terms for RNA polymerase I, nucleolar chromatin, the small-subunit processome, and the H/ACA snoRNP complex, but it deliberately avoids broad label-only buckets for all nucleolar snoRNPs or all preribosomal particles.

Evidence

GO:0005730 Gene Ontology cellular-component term for nucleolus.
GO:0031981 Gene Ontology cellular-component term for nuclear lumen.
GO:0030874 Gene Ontology cellular-component term for nucleolar chromatin.
GO:0005736 Gene Ontology cellular-component term for RNA polymerase I complex.
GO:0032040 Gene Ontology cellular-component term for small-subunit processome.
GO:0031429 Gene Ontology cellular-component term for box H/ACA snoRNP complex.
GO:0006360 Gene Ontology biological-process term for transcription by RNA polymerase I.
GO:0006364 Gene Ontology biological-process term for rRNA processing.
GO:0042254 Gene Ontology biological-process term for ribosome biogenesis.
DOI:10.1038/nrm2184 Boisvert et al. 2007, 'The multifunctional nucleolus', Nature Reviews Molecular Cell Biology.
DOI:10.1146/annurev.genet.33.1.261 Venema and Tollervey 1999, 'Ribosome Synthesis in Saccharomyces cerevisiae', Annual Review of Genetics.
DOI:10.1038/nature00769 Dragon et al. 2002, 'A large nucleolar U3 ribonucleoprotein required for 18S ribosomal RNA biogenesis', Nature.

Curation history

2026-09-12T05:06:53Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-12T05:07:48Z codex · EXPANDED_RECORD — Added nucleolar nuclear-lumen parthood, exact GO-grounded nucleolar-chromatin, RNA polymerase I, SSU processome, and box H/ACA snoRNP components, Eukaryota distribution, a Saccharomyces cerevisiae example, rDNA-transcription, rRNA-processing, and ribosome-biogenesis functions, DOI/GO evidence, a nonmechanistic ribosome-biogenesis graph, and a TODO for remaining preribosomal component boundaries.
2026-09-12T05:08:19Z codex · TIGHTENED_MODELING — Retyped nucleolar chromatin from bare DNA to OTHER, switched the Eukaryota distribution reference to GO:0005730, and relabeled the GO:0006360 function as transcription by RNA polymerase I.
2026-09-12T05:14:59Z codex · ADDRESSED_REVIEW — Resolved #588 by retyping the nucleolar chromatin graph node as a STRUCTURE, and resolved #589 by narrowing the RNA polymerase I graph edge to rDNA within nucleolar chromatin.
2026-09-20T21:51:50Z codex · ADDRESSED_REVIEW — Retyped the RNA polymerase I complex graph node from GENE_OR_PROTEIN to STRUCTURE.

Source: data/structures/other/nucleolus.yaml