small-subunit processome

GO:0032040 · Ribonucleoprotein · Ribonucleoprotein complex · Proposed

A large ribonucleoprotein complex that is an early preribosomal complex. In S. cerevisiae, it has a size of 80S and consists of the 35S pre-rRNA, early-associating ribosomal proteins most of which are part of the small ribosomal subunit, the U3 snoRNA and associated proteins. [GO:0032040]

Synonyms: small subunit processome; SSU processome

Part of: nucleolus (GO:0005730)

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
35S pre-rRNA and U3 snoRNA	Rna	part of	Reviewed label only (reviewed name; no accession asserted)				RNA constituents of the budding-yeast 80S small-subunit processome described by GO:0032040. `GO:0032040` GO:0032040 defines the S. cerevisiae small-subunit processome as containing the 35S pre-rRNA and U3 snoRNA.
small-subunit processome protein cohort	Protein	part of	Reviewed label only (reviewed name; no accession asserted)				Early-associating ribosomal proteins and associated proteins that accompany the RNA constituents in the small-subunit processome. `GO:0032040` GO:0032040 defines the S. cerevisiae small-subunit processome as containing early-associating ribosomal proteins and associated proteins.

Functions

rRNA processing GO:0006364 — The small-subunit processome is an early preribosomal ribonucleoprotein involved in precursor-rRNA processing during ribosome biogenesis.
- GO:0006364 GO:0006364 is the Gene Ontology biological-process term for rRNA processing.
- GO:0032040 GO:0032040 defines the small-subunit processome as an early preribosomal ribonucleoprotein complex.
maturation of SSU-rRNA GO:0030490 — The small-subunit processome supports maturation of the precursor small-subunit rRNA into mature SSU-rRNA.
- GO:0030490 GO:0030490 is the Gene Ontology biological-process term for maturation of precursor small-subunit rRNA.
- DOI:10.1038/nature00769 Dragon et al. 2002 characterized a large nucleolar U3 ribonucleoprotein required for 18S rRNA biogenesis.
ribosome biogenesis GO:0042254 — As an early preribosomal complex, the small-subunit processome contributes to assembly and maturation of ribosome-subunit constituents.
- GO:0042254 GO:0042254 is the Gene Ontology biological-process term for ribosome biogenesis.
- GO:0032040 GO:0032040 classifies the small-subunit processome as an early preribosomal complex.

Mechanism graphs

RNAs and proteins form the SSU processome (ASSEMBLY)

GO defines the small-subunit processome as an early nucleolar preribosomal ribonucleoprotein that contains 35S pre-rRNA, U3 snoRNA, early-associating small-subunit ribosomal proteins and associated proteins in S. cerevisiae.

Subject	Predicate	Object	Evidence
35S pre-rRNA and U3 snoRNA	contributes constituents to	small-subunit processome	`GO:0032040` GO:0032040 defines the budding-yeast complex as containing 35S pre-rRNA and U3 snoRNA.
small-subunit processome protein cohort	contributes constituents to	small-subunit processome	`GO:0032040` GO:0032040 defines the budding-yeast complex as containing early-associating ribosomal proteins and associated proteins.
small-subunit processome	localizes to	nucleolus	`GO:0032040` GO:0032040 carries a part_of relationship to the nucleolus. `GO:0005730` GO:0005730 is the nucleolus cellular-component term.
small-subunit processome	supports	maturation of SSU-rRNA	`DOI:10.1038/nature00769` Dragon et al. 2002 characterized a large nucleolar U3 ribonucleoprotein required for 18S rRNA biogenesis. `GO:0030490` GO:0030490 is the biological-process term for SSU-rRNA maturation.

Discussions

CURATION_TODO (OPEN): Resolve exact SSU processome RNA, ribosomal-protein, U3-associated-protein and 90S-boundary components. GO:0032040 defines an S. cerevisiae 80S SSU processome with 35S pre-rRNA, U3 snoRNA, early-associating small-subunit ribosomal proteins and associated proteins. Exact source-neutral RNA and protein-family groundings, plus the boundary between the GO:0032040 SSU processome and the related GO:0030686 90S preribosome sibling, need a narrower literature-backed curation pass.

Evidence

GO:0032040 Gene Ontology cellular-component term for the small-subunit processome and its exact synonyms.
GO:0030684 Gene Ontology cellular-component parent term for preribosomal complexes.
GO:0140513 Gene Ontology cellular-component parent term for nuclear protein-containing complexes.
GO:0005730 Gene Ontology cellular-component term for the nucleolus.
GO:0006364 Gene Ontology biological-process term for rRNA processing.
GO:0030490 Gene Ontology biological-process term for maturation of SSU-rRNA.
GO:0042254 Gene Ontology biological-process term for ribosome biogenesis.
PMID:12068309 Publication cited in GO:0032040 definition xrefs.
PMID:12957375 Publication cited in GO:0032040 definition xrefs.
PMID:15120992 Publication cited in GO:0032040 definition xrefs.
PMID:15590835 Publication cited in GO:0032040 definition xrefs.
DOI:10.1038/nature00769 Dragon et al. 2002, 'A large nucleolar U3 ribonucleoprotein required for 18S ribosomal RNA biogenesis', Nature.

Curation history

2026-09-25T17:27:04Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-25T17:28:22Z codex · EXPANDED_RECORD — Added GO exact synonyms, preribosome parentage, nucleolar parthood, reviewed-label-only SSU-processome RNA and protein cohorts, rRNA processing functions, GO/PubMed evidence, a conservative assembly graph and a TODO for exact SSU-processome component boundaries.
2026-09-25T17:39:31Z codex · ADDRESS_REVIEW — Resolved PR #1590 review issue #1591 by rewording the GO:0030686 90S preribosome as a related sibling boundary instead of a broader SSU-processome parent.

Source: data/structures/ribonucleoprotein/small_subunit_processome.yaml