RRB1 encodes an essential nucleolar WD-repeat ribosome assembly factor that binds and chaperones ribosomal protein L3/Rpl3 during early 60S ribosomal subunit biogenesis. Rrb1 promotes soluble, assembly-competent Rpl3 delivery to preribosomal particles, supports 25S rRNA maturation, and is required for normal production of free 60S subunits. Its conserved PANTHER family (PTHR45903:SF1) includes fungal Rrb1/GRWD1-like proteins with roles in ribosome assembly, but the yeast literature supports an Rpl3-specific chaperone role rather than generic protein binding.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005730 nucleolus | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic nucleolar localization is consistent with Rrb1's experimentally supported site of action in early 60S biogenesis. Reason: Rrb1 is a nuclear/nucleolar WD-repeat protein and the conserved family context supports a nuclear ribosome-assembly role. Supporting Evidence: PMID:26112308 Rrb1, which is a mostly nucleolar protein, binds to Rpl3 file:interpro/panther/PTHR45903/PTHR45903-metadata.yaml Some family members are implicated in ribosome biogenesis |
| GO:0042254 ribosome biogenesis | IBA GO_REF:0000033 | MODIFY | Summary: The biological-process inference is correct but should be made more specific to large ribosomal subunit biogenesis. Reason: Experimental studies show Rrb1 functions through Rpl3 in early 60S subunit assembly, not general ribosome biogenesis across both subunits. Proposed replacements: ribosomal large subunit biogenesis Supporting Evidence: PMID:11728313 Impairment of Rrb1p function results in decreased levels of free 60S ribosomal subunits. file:yeast/RRB1/RRB1-deep-research-falcon.md early large (60S) subunit biogenesis |
| GO:0005634 nucleus | IEA GO_REF:0000044 | MODIFY | Summary: Nuclear localization is true but too broad given direct nucleolar evidence. Reason: The functional site is best represented by nucleolus, where early preribosomal assembly occurs and where Rrb1 is enriched. Proposed replacements: nucleolus Supporting Evidence: PMID:26112308 Rrb1, which is a mostly nucleolar protein |
| GO:0006364 rRNA processing | IEA GO_REF:0000043 | ACCEPT | Summary: Retain as a supported large-subunit biogenesis consequence of Rrb1 function. Reason: Rrb1 depletion impairs 25S rRNA maturation, so rRNA processing is a valid process annotation, although the mechanistic core is Rpl3 chaperoning during 60S assembly. Supporting Evidence: file:yeast/RRB1/RRB1-deep-research-falcon.md including efficient 25S rRNA maturation and production of 60S subunits |
| GO:0042254 ribosome biogenesis | IEA GO_REF:0000043 | MODIFY | Summary: The UniProt keyword mapping captures the correct pathway but is less specific than the evidence warrants. Reason: Rrb1 acts in early large ribosomal subunit biogenesis through Rpl3 rather than generic ribosome biogenesis. Proposed replacements: ribosomal large subunit biogenesis Supporting Evidence: PMID:11728313 required for proper assembly of preribosomal particles during early ribosome biogenesis, presumably by targeting L3 onto the 35S precursor rRNA |
| GO:0005515 protein binding | IPI PMID:14759368 High-definition macromolecular composition of yeast RNA-proc... | MARK AS OVER ANNOTATED | Summary: Generic protein binding from a high-throughput complex study is not informative for Rrb1 function. Reason: Rrb1's specific function is Rpl3 chaperoning during large-subunit biogenesis; a generic protein binding annotation should not be treated as a core molecular function. Supporting Evidence: PMID:26112308 dedicated chaperone proteins recognize the N-terminal regions of ribosomal proteins |
| GO:0005515 protein binding | IPI PMID:16554755 Global landscape of protein complexes in the yeast Saccharom... | MARK AS OVER ANNOTATED | Summary: High-throughput interaction data are consistent with complex membership but too generic for molecular-function curation. Reason: The interactions should be interpreted in the context of Rpl3 chaperoning and 60S assembly, not as a standalone protein binding function. Supporting Evidence: PMID:26112308 Rrb1 and Sqt1 interact with the very N-terminal residues of Rpl3 and Rpl10, respectively. |
| GO:0005515 protein binding | IPI PMID:37968396 The social and structural architecture of the yeast protein ... | MARK AS OVER ANNOTATED | Summary: Interactome-derived protein binding is too broad to represent Rrb1's curated activity. Reason: The core activity is substrate-specific ribosomal protein chaperoning; the generic term should not be accepted. Supporting Evidence: file:yeast/RRB1/RRB1-deep-research-falcon.md Rrb1 is part of the broader dedicated chaperone/co-translational capture paradigm for ribosomal proteins. |
| GO:0051082 unfolded protein binding | IDA PMID:26112308 Co-translational capturing of nascent ribosomal proteins by ... | MODIFY | Summary: The experiment supports chaperoning of nascent Rpl3, but unfolded protein binding is too generic. Reason: Rrb1 captures a specific ribosomal protein client and promotes delivery to the assembly site, which is better represented as protein carrier chaperone activity. Proposed replacements: protein carrier chaperone Supporting Evidence: PMID:26112308 Rrb1, Syo1, Sqt1 and Yar1 selectively enriched the mRNAs encoding their specific ribosomal protein clients |
| GO:0005730 nucleolus | IDA PMID:10684247 The yeast nuclear pore complex: composition, architecture, a... | ACCEPT | Summary: Direct nucleolar localization is consistent with Rrb1's early pre-60S assembly role. Reason: Nucleolar enrichment matches the site of early ribosome biogenesis and is supported by independent literature synthesis. Supporting Evidence: file:yeast/RRB1/RRB1-deep-research-falcon.md Rrb1 is predominantly nuclear with strong nucleolar enrichment |
| GO:0042254 ribosome biogenesis | IMP PMID:11728313 A yeast homolog of chromatin assembly factor 1 is involved i... | MODIFY | Summary: The mutant phenotype supports ribosome biogenesis, but the more precise process is large subunit biogenesis. Reason: Loss of Rrb1 specifically reduces free 60S subunits and disrupts early preribosomal assembly through Rpl3. Proposed replacements: ribosomal large subunit biogenesis Supporting Evidence: PMID:11728313 Impairment of Rrb1p function results in decreased levels of free 60S ribosomal subunits. |
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Download this section (compressed HTML)Q: What is the direct binding interface and stoichiometry of the yeast Rrb1-Rpl3 complex during co-translational capture?
Suggested experts: ribosome biogenesis experts, structural biologists
Q: Does Rrb1 hand Rpl3 directly to pre-60S particles in the nucleolus, or through an intermediate import or assembly factor?
Suggested experts: yeast ribosome assembly researchers
Experiment: Reconstitute the yeast Rrb1-Rpl3 N-terminal peptide or full-client complex and solve its structure by cryo-EM, crystallography, or crosslinking-MS to define the chaperone-client interface.
Hypothesis: Rrb1 recognizes a defined Rpl3 segment that is later buried in the 60S subunit and shields it before assembly.
Type: structural biochemistry
Experiment: Combine acute RRB1 depletion with Rpl3 pulse labeling, nuclear import assays, and pre-60S immunoprecipitation to test whether Rrb1 primarily affects Rpl3 solubility, nuclear import, or loading onto preribosomes.
Hypothesis: Rrb1 loss reduces productive Rpl3 loading onto early pre-60S particles before detectable global rRNA-processing defects.
Type: pulse-chase ribosome assembly assay
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