PNO1 encodes Pno1/Dim2/Rrp20, a conserved KH-domain ribosome biogenesis factor required for small ribosomal subunit synthesis. Pno1 binds pre-rRNA, especially the ITS1 region, participates in early SSU processome and 90S to pre-40S transitions, supports pre-40S export from the nucleus, and works with Nob1 and Rio1 during late cytoplasmic 20S pre-rRNA to 18S rRNA maturation. The coherent core function is RNA-binding regulation of SSU/pre-40S assembly and processing; older proteasome and generic chaperone annotations appear secondary or overextended.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005634 nucleus | IBA GO_REF:0000033 | ACCEPT | Summary: PANTHER IBA to nucleus is consistent with Pno1's conserved role as a nuclear/nucleolar and nucleocytoplasmic ribosome biogenesis factor. Reason: Pno1 acts in nuclear and nucleolar stages of SSU biogenesis and has direct experimental nuclear/nucleolar localization support. |
| GO:0003723 RNA binding | IEA GO_REF:0000120 | ACCEPT | Summary: Automated RNA-binding annotation is supported by Pno1 KH domains and by direct evidence for binding pre-rRNA/ITS1. Reason: RNA binding is a core molecular function for Pno1, though the more specific rRNA primary transcript binding term is preferred when available. Supporting Evidence: file:yeast/PNO1/PNO1-deep-research-falcon.md binds pre-rRNA (ITS1 region) via its KH domain |
| GO:0005730 nucleolus | IEA GO_REF:0000120 | ACCEPT | Summary: UniProt/ARBA nucleolus mapping is consistent with Pno1 function in early nucleolar SSU processome assembly and pre-rRNA processing. Reason: The nucleolus is a supported compartment for Pno1 during early ribosome biogenesis. |
| GO:0005737 cytoplasm | IEA GO_REF:0000044 | ACCEPT | Summary: Cytoplasmic localization is consistent with Pno1 shuttling and late cytoplasmic pre-40S maturation. Reason: Pno1 functions after pre-40S export as part of late 18S rRNA maturation and quality-control gating. |
| GO:0042254 ribosome biogenesis | IEA GO_REF:0000120 | ACCEPT | Summary: Broad automated ribosome biogenesis annotation accurately summarizes the experimentally supported Pno1 role in SSU/pre-40S assembly and maturation. Reason: Pno1 is a ribosome biogenesis factor; more specific annotations capture SSU-rRNA maturation, pre-40S export, and ribosome assembly. |
| GO:0005730 nucleolus | IDA PMID:27980088 Architecture of the yeast small subunit processome. | ACCEPT | Summary: ComplexPortal direct assay evidence places Pno1 in the nucleolus/SSU processome context. Reason: Nucleolar localization matches Pno1's early SSU processome and pre-rRNA processing roles. Supporting Evidence: PMID:27980088 Architecture of the yeast small subunit processome. |
| GO:0030490 maturation of SSU-rRNA | NAS PMID:15489292 RNA polymerase I transcription and pre-rRNA processing are l... | ACCEPT | Summary: Curated statement evidence supports Pno1 as a specific SSU processome component linked to SSU-rRNA maturation. Reason: The annotation is consistent with multiple yeast studies showing defects in pre-rRNA processing when Pno1/Dim2/Rrp20 is perturbed. Supporting Evidence: PMID:15489292 RNA polymerase I transcription and pre-rRNA processing are linked by specific SSU processome components. |
| GO:0000056 ribosomal small subunit export from nucleus | IMP PMID:18755838 TOR regulates the subcellular distribution of DIM2, a KH dom... | ACCEPT | Summary: Mutant phenotype evidence supports Dim2/Pno1 involvement in pre-40S export from the nucleus. Reason: Pno1 contains a conserved export-related region and perturbation causes pre-40S export defects, making this a core process annotation. Supporting Evidence: PMID:18755838 pre-40S ribosome export |
| GO:0042134 rRNA primary transcript binding | IDA PMID:18755838 TOR regulates the subcellular distribution of DIM2, a KH dom... | ACCEPT | Summary: Direct assay evidence shows Dim2/Pno1 binds pre-rRNA through its KH domain at the 5' end of ITS1. Reason: This is the most specific experimentally supported molecular function for Pno1 and should be considered core. Supporting Evidence: PMID:18755838 DIM2 binds pre-rRNAs directly through its KH domain |
| GO:0042255 ribosome assembly | IMP PMID:18755838 TOR regulates the subcellular distribution of DIM2, a KH dom... | ACCEPT | Summary: Mutant phenotype evidence supports Dim2/Pno1 function in cotranscriptional ribosome assembly and pre-40S maturation. Reason: Pno1 coordinates pre-rRNA binding, pre-40S export, and later maturation, so ribosome assembly is appropriate. Supporting Evidence: PMID:18755838 cotranscriptional ribosome assembly |
| GO:0030686 90S preribosome | HDA PMID:12150911 90S pre-ribosomes include the 35S pre-rRNA, the U3 snoRNP, a... | ACCEPT | Summary: High-throughput direct assay evidence identifies Pno1/Rrp20 with 90S preribosomal particles. Reason: This component annotation is consistent with Pno1's early SSU processome role. Supporting Evidence: PMID:12150911 90S pre-ribosomes include the 35S pre-rRNA |
| GO:0043248 proteasome assembly | IMP PMID:12502737 Nob1p is required for biogenesis of the 26S proteasome and d... | MARK AS OVER ANNOTATED | Summary: The 2002 Nob1/Pno1 study connected pno1 defects with Pre6p accumulation and proteasome maturation, but subsequent literature and UniProt support a primary SSU ribosome biogenesis role for Pno1. Reason: PMID:12502737 directly reports pno1 mutant proteasome maturation defects, but later Pno1/Dim2 literature supports ribosome biogenesis, pre-rRNA processing, and pre-40S maturation as the conserved core function. This proteasome assembly annotation is therefore retained only as a non-core/over-annotated phenotype from an older model. Supporting Evidence: PMID:12502737 A defect in either NOB1 or PNO1 caused accumulation of newly formed Pre6p |
| GO:0043248 proteasome assembly | IPI PMID:12502737 Nob1p is required for biogenesis of the 26S proteasome and d... | MARK AS OVER ANNOTATED | Summary: The protein-interaction basis for proteasome assembly is not sufficient to override the now well-supported Pno1 role in SSU/pre-40S maturation. Reason: The original paper did observe proteasome assembly defects in pno1 mutants, but the current weight of evidence places Pno1 as a Dim2/Rrp20 ribosome biogenesis factor. The proteasome annotation should therefore be treated as an over-annotated non-core phenotype rather than a primary molecular role. Supporting Evidence: PMID:12502737 temperature-sensitive nob1 and pno1 mutants exhibited defects in the processing of the beta subunits and in the assembly of the 20S and the 26S proteasomes |
| GO:0000447 endonucleolytic cleavage in ITS1 to separate SSU-rRNA from 5.8S rRNA and LSU-rRNA from tricistronic rRNA transcript (SSU-rRNA, 5.8S rRNA, LSU-rRNA) | IMP PMID:12736301 RRP20, a component of the 90S preribosome, is required for p... | ACCEPT | Summary: RRP20/PNO1 mutant phenotypes impair early pre-rRNA cleavages, including ITS1 processing that separates SSU from LSU rRNA precursors. Reason: Pno1 is required for proper pre-rRNA processing as part of the SSU maturation pathway, although it is not itself the nuclease. Supporting Evidence: PMID:12736301 RRP20, a component of the 90S preribosome, is required for pre-18S rRNA processing |
| GO:0000472 endonucleolytic cleavage to generate mature 5'-end of SSU-rRNA from (SSU-rRNA, 5.8S rRNA, LSU-rRNA) | IMP PMID:12736301 RRP20, a component of the 90S preribosome, is required for p... | ACCEPT | Summary: PNO1/RRP20 mutant evidence supports a requirement for proper pre-18S rRNA processing and mature SSU-rRNA formation. Reason: The annotation captures a core process consequence of Pno1 function in SSU maturation. Supporting Evidence: PMID:12736301 defective in ribosomal RNA processing |
| GO:0005634 nucleus | IDA PMID:12502737 Nob1p is required for biogenesis of the 26S proteasome and d... | ACCEPT | Summary: Direct assay evidence supports nuclear localization of Pno1. Reason: Nuclear localization is consistent with Pno1's early pre-rRNA processing and pre-40S export roles. Supporting Evidence: PMID:12502737 Nob1p is a nuclear protein that forms a complex with the 19S regulatory particle of the 26S proteasome and with uncharacterized nuclear protein Pno1p |
| GO:0005730 nucleolus | IDA PMID:10923024 Functional analysis of six genes from chromosomes XIV and XV... | ACCEPT | Summary: Direct GFP localization evidence places Yor145c/Pno1 in the nucleolus. Reason: Nucleolar localization is appropriate for an early SSU processome and pre-rRNA processing factor. Supporting Evidence: PMID:10923024 Yor145-GFP concentrating in the nucleolus |
| GO:0051082 unfolded protein binding | IDA PMID:12502737 Nob1p is required for biogenesis of the 26S proteasome and d... | MARK AS OVER ANNOTATED | Summary: The unfolded-protein binding annotation is not well aligned with Pno1's demonstrated KH-domain pre-rRNA binding and ribosome biogenesis functions. Reason: Pno1 should not be curated as a generic protein-folding chaperone. Its supported molecular function is rRNA/pre-rRNA binding and assembly-factor regulation with Nob1/Rio1. |
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Download this section (compressed HTML)Q: Should the legacy PNO1 proteasome assembly annotations be retired or replaced by updated pre-40S/Nob1 maturation annotations in upstream SGD/GO curation?
Experiment: Revisit proteasome assembly phenotypes in pno1/dim2 mutants using acute degron depletion and ribosome-processing rescue constructs to distinguish direct proteasome effects from secondary consequences of impaired ribosome biogenesis.
Hypothesis: The reported proteasome maturation defects are indirect consequences of perturbed Nob1/Pno1 ribosome biogenesis or pleiotropic essential-gene stress.
Type: conditional depletion/rescue
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