NCU08595 encodes the Neurospora crassa ortholog of ribosome production factor 2 (Rpf2), a 341-residue nucleolar assembly factor of the large ribosomal subunit built around a Brix domain. In fungal orthologs, Rpf2 forms an obligate heterodimer with Rrs1 in which Rrs1 completes the Brix fold. Rpf2 binds 5S rRNA directly, through a conserved basic KKR loop that inserts into 5S rRNA loop E, and contacts ribosomal protein uL18 (RpL5). The heterodimer recruits the 5S ribonucleoprotein particle (5S rRNA, uL18 and uL5) into early nucleolar pre-60S particles. It then holds the immature central protuberance in place until Rpf2-Rrs1 is released, which allows the 5S RNP to rotate into its mature position. This assembly step is required for processing of 27SB pre-rRNA to mature 25S/28S and 5.8S rRNA. Rpf2 has no catalytic activity; it acts as an RNA- and protein-binding scaffold.
Summary: Core process. Rpf2-Rrs1 recruits the 5S RNP into nucleolar pre-60S particles and holds the immature central protuberance in place, so the protein does part of the work of large-subunit assembly itself.
Reason: This IEA comes from the Rpf2-specific InterPro entry IPR039770, not from the generic Brix signature. UniProt places NCU08595 in PANTHER PTHR12728:SF0 (RIBOSOME PRODUCTION FACTOR 2 HOMOLOG), the same subfamily as the characterized Thermochaetoides (Chaetomium) thermophilum and S. cerevisiae Rpf2 proteins. The C. thermophilum protein is 74% identical to NCU08595 and also belongs to the Sordariales. Structural and biochemical work on fungal Rpf2-Rrs1 shows the complex binding 5S rRNA, RpL5 and Rsa4 and positioning the 5S RNP within the pre-60S particle. That is direct physical participation in assembly, not just a requirement for it. This is the most accurate process term for the gene.
Our data provide a structural model for 5S RNP recruitment to the pre-60S particle and explain why removal of Rpf2-Rrs1 is necessary for rearrangements to drive 60S maturation.
file:NEUCR/NCU08595/NCU08595-uniprot.txt
DR PANTHER; PTHR12728:SF0; RIBOSOME PRODUCTION FACTOR 2 HOMOLOG; 1.
GO:0000463 maturation of LSU-rRNA from tricistronic rRNA transcript (SSU-rRNA, 5.8S rRNA, LSU-rRNA)
IBA GO_REF:0000033
ACCEPT
Summary: The PAINT node PTN000296192 (Rpf2 clade) was seeded by S. cerevisiae RPF2, which is required for processing of 27SB pre-rRNA. NCU08595 is in the same PANTHER subfamily.
Reason: The IBA rests on a curator-placed node in the Rpf2 subfamily (SF0), and NCU08595 descends from it. Nothing in the target sequence suggests the function was lost; the 5S rRNA-binding KKR loop and the residue aligned to yeast R236 are both conserved (file:NEUCR/NCU08595/NCU08595-bioinformatics/RESULTS-rereview.md). Rpf2-Rrs1 is a structural component of the pre-60S particles in which 27SB pre-rRNA is processed, and GO conventionally annotates such non-catalytic assembly factors to LSU-rRNA maturation. The processing is a downstream consequence of 5S RNP assembly, so GO:0000027 remains the primary process. This term is still the specific rRNA-maturation process the gene carries, and the broader IEA terms below are refined to it. A single donor is not weak support for a PAINT node.
Summary: Correct but general. The more specific descendant GO:0000463, which the gene already carries by IBA, is supported.
Reason: GO:0000463, maturation of LSU-rRNA from the tricistronic rRNA transcript, is a descendant of this term and is already on NCU08595 from the PAINT Rpf2 node. In fungi, Rpf2-dependent processing is the 27SB-to-25S/5.8S step of the tricistronic 35S precursor. The previous review accepted this term as it stood; the correct-but-general rule calls for refining it to the term the gene already carries.
Summary: Nucleolar localization is supported by experimental evidence from plant, fly, yeast, apicomplexan and human Rpf2 orthologs, and agrees with the stage of assembly at which Rpf2-Rrs1 acts.
Reason: The PAINT node is supported by orthologs from several kingdoms, which puts nucleolar residence deep in the Rpf2 lineage, and NCU08595 descends from that node. Rpf2-Rrs1 joins the 90S and early pre-60S particles, which form in the nucleolus. No direct localization experiment exists for NCU08595 itself.
Summary: Same nucleolar claim as the IBA row, here from the UniRule/RuleBase Rpf2 family rule.
Reason: This row is consistent with the IBA nucleolus annotation, and the function is performed in nucleolar pre-ribosomes. The ARBA part of the UniProt subcellular-location statement is not used as support; the conserved ortholog localization and the pathway stage are the evidence.
Summary: This generic Brix-domain mapping is true but too broad. The supported specific process is LSU-rRNA maturation from the tricistronic transcript.
Reason: The InterPro Brix signature IPR007109 covers several paralogous families (Rpf2, Rpf1, Imp4, Brx1, Ssf1/2). Each of these has a different role in pre-rRNA processing, so the generic mapping can only give rRNA processing. The Rpf2 subfamily membership of NCU08595 supports the specific term GO:0000463, which the gene already carries by IBA.
Summary: Correct but general. Rpf2 binds 5S rRNA specifically, and this was shown directly for the 74%-identical C. thermophilum ortholog, which is in the same order as Neurospora.
Reason: The PAINT rRNA-binding node is sound. The specific RNA ligand is 5S rRNA, which is the molecular basis of the Rpf2 role in assembly. Sinning and colleagues showed by EMSA that C. thermophilum Rpf2 alone binds 5S rRNA. In the A. nidulans structure, the conserved KKR loop inserts into the major groove of 5S rRNA loop E. Yao and colleagues showed that the Rpf2-Rrs1 complex binds 5S rRNA and that yeast Rpf2 R236 contributes to this binding. NCU08595 keeps the KKR loop (K94-K96) and the arginine aligned to yeast R236 (R242). The structural docking also places Rpf2 against 25S pre-rRNA, but that contact has not been tested biochemically, so 5S rRNA binding is the descendant that is supported.
Propagation Review
Root cause:TERM SCOPING PROBLEM
Sources checked:
PANTHER:PTN000296192 Β· PTN000296192 SUPPORTS TRANSFER
RNA binding is conserved across the Rpf2 node, and NCU08595 (PTHR12728:SF0) is inside the clade with its 5S rRNA-contacting residues intact. The MODIFY only sharpens the term to 5S rRNA binding; it does not dispute the transfer.
Summary: Same claim as the IBA rRNA-binding row, here from combined InterPro/UniRule mapping. It is refined in the same way to 5S rRNA binding.
Reason: This row is consistent with the IBA row on the same term. The Rpf2-specific family evidence supports the more precise 5S rRNA binding term (see the IBA row for the experimental basis in Sordariomycete and other fungal orthologs).
Summary: True but very broad. The supported specific processes are ribosomal large subunit assembly and LSU-rRNA maturation.
Reason: The ARBA rule is not independent evidence, but the claim is correct. The specific descendants GO:0000027 (ribosomal large subunit assembly, the core process) and GO:0000463 (LSU-rRNA maturation) are both supported and both already on the gene.
Our data provide a structural model for 5S RNP recruitment to the pre-60S particle and explain why removal of Rpf2-Rrs1 is necessary for rearrangements to drive 60S maturation.
Core Functions
Binds 5S rRNA, together with its partner Rrs1, through the conserved Brix-domain KKR loop, and recruits the 5S ribonucleoprotein particle into nucleolar pre-60S particles. It holds the immature central protuberance in place until it is released, and so acts as a non-catalytic scaffold in assembly of the large ribosomal subunit.
Our data provide a structural model for 5S RNP recruitment to the pre-60S particle and explain why removal of Rpf2-Rrs1 is necessary for rearrangements to drive 60S maturation.
Q: Does the N. crassa Rpf2-Rrs1 heterodimer bind 5S rRNA through K94-K96 and R242, as the fungal ortholog data predict?
Q: Should the 5S RNP-recruiting role of Rpf2-Rrs1 be recorded in GO-CAM as input to the 5S RNP incorporation step, rather than only as rRNA-processing process terms?
Suggested Experiments
Experiment: Make a conditional or heterokaryon-maintained NCU08595 depletion strain and run Northern blots of pre-rRNA intermediates and polysome profiles to test for 27SB accumulation and loss of 60S subunits.
Type: genetic depletion with pre-rRNA analysis
Experiment: Run EMSA of recombinant N. crassa Rpf2-Rrs1 (wild type and K94A/K95A/R96A and R242A variants) with N. crassa 5S rRNA.
Type: in vitro RNA binding
External Prediction Reviews
These computational predictions are reviewed separately from the GOA annotation set used for this review. The assessments below are from this project and do not constitute official GO annotations or endorsement by GO/UniProt. They are not included in the existing annotation review above.
NCU08595 is a Rpf2-family ribosome assembly factor with a Brix RNA-binding domain. By conservation with characterized fungal Rpf2, it associates with Rrs1, binds 5S rRNA and promotes incorporation of the 5S ribonucleoprotein particle into nucleolar large-subunit precursors. This assembly step supports large-subunit rRNA maturation.
Review rationale: Correct but less precise than an existing supported annotation. NCU08595 is in the Rpf2 subfamily (InterPro IPR039770; PANTHER PTHR12728:SF0), and characterized fungal Rpf2-Rrs1 complexes bind 5S rRNA, recruit the 5S RNP into pre-60S particles and are required for 27SB pre-rRNA processing, so participation in LSU-rRNA maturation transfers by subfamily membership. The predicted term is already in GOA for this gene as an InterPro2GO IEA, and the gene carries its is_a descendant GO:0000463 (maturation of LSU-rRNA from tricistronic rRNA transcript) by IBA from the PAINT Rpf2 node. The gene review refines GO:0000470 to GO:0000463, so the prediction is the general form of the supported specific process. A PubMed search found no Neurospora-specific study of NCU08595; support rests on the fungal orthologs. Participation is as a non-catalytic assembly scaffold, not nuclease chemistry.
Supporting Evidence:
PMID:25855814: "Proteins Rpf2 and Rrs1 are required for 60S ribosomal subunit maturation."
PMID:25855814: "to the 90S ribosome precursor and subsequent 27SB pre-rRNA processing."
PMID:26117542: "These data show that Rpf2 directly binds the 5S rRNA."