mug151 (systematic name SPAC3H1.03) encodes a 146-residue protein of the Schizosaccharomyces pombe SAP30BP/HCNGP family (Pfam PF07818; InterPro IPR012479; PANTHER PTHR13464:SF0). The protein has a charged, predicted-disordered N-terminal region followed by the conserved HCNGP region, and UniProt predicts nuclear localization by similarity. Human SAP30BP has been implicated in transcriptional control and directly acts with RBM17/SPF45 in splicing a subset of short introns, but neither activity has been demonstrated for mug151. Its direct molecular activity and biological process therefore remain unknown. The gene was named from its meiotic transcriptional up-regulation; a specific meiotic mechanism has not been established for mug151 in accessible gene-specific literature.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005634 nucleus | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: Nuclear localization inferred from the UniProtKB/Swiss-Prot subcellular-location mapping (UniProt records "SUBCELLULAR LOCATION: Nucleus" by similarity, ECO:0000250). This is consistent with the SAP30BP/HCNGP family, whose members are nuclear transcription/splicing regulators, and the protein has no transmembrane or signal features. It is a reasonable localization inference, though not experimentally verified for the S. pombe protein, and describes where the protein is rather than what it does. Reason: Well-supported localization inference (family + UniProt by-similarity), but it is a cellular-component annotation and not a direct statement of molecular function; retained as non-core context. Supporting Evidence: file:SCHPO/mug151/mug151-uniprot.txt SUBCELLULAR LOCATION: Nucleus {ECO:0000250}. |
| GO:0006355 regulation of DNA-templated transcription | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: Domain-based (InterPro IPR012479, SAP30BP; PANTHER PTHR13464 "transcriptional regulator protein HCNGP") inference of a transcriptional-regulation role. This is the best-supported functional hypothesis from the family assignment, and is broadly consistent with the SAP30/Sin3-HDAC association reported for the animal ortholog. However, it is unproven for the S. pombe protein, and the same family also has a documented pre-mRNA splicing role (via RBM17/SPF45), so transcription regulation is a plausible but not exclusive or established function here. Reason: Reasonable domain-family inference, retained as a plausible (non-core) role. Meiotic up-regulation and family membership do not establish that mug151 actually regulates transcription in S. pombe; there is no experimental support, and the family has an alternative splicing function. Not promoted to a core function. Supporting Evidence: file:SCHPO/mug151/mug151-uniprot.txt DR GO; GO:0006355; P:regulation of DNA-templated transcription; IEA:InterPro. PMID:38065098 Here, we demonstrate that SAP30BP, a factor previously implicated in transcriptional control, is an essential splicing cofactor for RBM17. file:SCHPO/mug151/mug151-deep-research-falcon.md A non-enzymatic nuclear regulatory/adaptor role is plausible but unvalidated. |
| GO:0003674 molecular_function | ND GO_REF:0000015 | ACCEPT | Summary: PomBase "no data" (ND) placeholder recording that no molecular function has been experimentally determined for mug151. This accurately reflects the current state of knowledge for this dark gene: the direct molecular activity has never been assayed in S. pombe. Reason: Honest reflection of the knowledge state. No experimental molecular-function data exist; the family-based transcription/splicing hypotheses are captured in knowledge_gaps and suggested_questions rather than asserted as function. Supporting Evidence: file:SCHPO/mug151/mug151-deep-research-falcon.md No experimentally demonstrated molecular function was found for Mug151. |
| GO:0005575 cellular_component | ND GO_REF:0000015 | ACCEPT | Summary: PomBase "no data" (ND) placeholder for the cellular component where the gene product is active. A by-similarity nuclear localization is separately captured by the UniProt/SubCell IEA annotation (GO:0005634). Reason: Accurate ND placeholder; the specific active site/component in S. pombe has not been experimentally established. The nuclear localization is retained via the GO:0005634 IEA annotation. Supporting Evidence: file:SCHPO/mug151/mug151-deep-research-falcon.md Mug151’s localization is **unknown** from the evidence retrieved. |
| GO:0008150 biological_process | ND GO_REF:0000015 | UNDECIDED | Summary: PomBase records a "no data" (ND) biological-process placeholder, while UniProt separately asserts an experimentally supported role in meiosis from PMID:16303567 and maps the meiosis keyword to GO:0051321. Because the cached paper is abstract-only and does not mention mug151, the gene-specific experimental basis and appropriate process specificity cannot be assessed here. Reason: The PomBase ND row accurately records its current knowledge state, but the inaccessible full text underlies a separate UniProt ECO:0000269 meiosis claim. Per curator-deference guidance, leave this annotation undecided rather than accepting ND as if no experimental claim existed or overruling UniProt from the abstract alone. Supporting Evidence: file:SCHPO/mug151/mug151-uniprot.txt FUNCTION: Has a role in meiosis. {ECO:0000269|PubMed:16303567}. file:SCHPO/mug151/mug151-deep-research-falcon.md No defensible placement of Mug151 in TOR signaling, mating-pheromone signaling, autophagy, DNA-damage signaling, RNA processing, or a chromatin-modifying complex was found. |
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Download this section (compressed HTML)Q: Does S. pombe mug151 function as a transcriptional co-regulator associated with a Sin3/HDAC (Clr6-type) co-repressor complex, as suggested by its SAP30BP/HCNGP family assignment and the InterPro/PomBase transcription-regulation annotations?
Q: Alternatively (or additionally), does mug151 act as a pre-mRNA splicing cofactor for a fission-yeast RBM17/SPF45-type factor, mirroring the characterized human SAP30BP splicing role on short introns?
Q: What mug151-specific experiment in the full text of PMID:16303567 supports UniProt's ECO:0000269 "role in meiosis" assertion, and does it justify GO:0051321 (meiotic cell cycle) or a more specific biological-process term?
Experiment: Affinity-purify tagged mug151 from S. pombe extracts followed by mass spectrometry to identify stable interaction partners; specifically test for co-purification with Sin3/HDAC (e.g. Clr6 complex) subunits and with any RBM17/SPF45-type splicing factor.
Hypothesis: mug151 physically associates with the SAP30/Sin3-HDAC co-repressor machinery in fission yeast.
Type: affinity purification-mass spectrometry
Experiment: Perform RNA-seq (with intron-retention/splicing analysis) comparing wild-type and mug151-deletion strains during vegetative growth and during meiosis, to distinguish a transcriptional-regulation phenotype from a splicing phenotype and to identify any target transcripts.
Hypothesis: mug151 influences transcription and/or splicing of a defined set of transcripts.
Type: comparative transcriptomics / splicing analysis
Experiment: Quantify meiotic progression, recombination, spore viability, and chromosome segregation fidelity in mug151-deletion crosses, using assays comparable to those that scored the seven critical genes in the 2005 meiotic screen.
Hypothesis: mug151 has a meiosis-specific role not detectable in standard viability screens.
Type: meiotic phenotyping
What is not known — curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: The direct molecular function of S. pombe mug151 is undetermined: no catalytic, binding, or other biochemical activity has been experimentally assayed for the protein, and its assignment to the SAP30BP/HCNGP family is purely by sequence and domain conservation.
OPEN BIOLOGY MF_DARK
What is known: What is firmly established is that mug151 is a small protein carrying the conserved HCNGP domain (Pfam PF07818) of the SAP30BP family; nuclear localization is predicted only by similarity. Human SAP30BP is implicated in transcriptional control and has a directly demonstrated splicing-cofactor activity for RBM17/SPF45. The gap is which, if either, of these activities mug151 performs in fission yeast.
Significance: mug151 is a conserved, HCNGP-domain, predicted nuclear protein whose family sits at the intersection of chromatin-linked transcriptional repression and pre-mRNA splicing; determining which activity operates in a genetically tractable single-celled eukaryote would clarify the ancestral function of the family and whether the human transcription and splicing roles are separable, related activities.
What would resolve it: Biochemical and interaction studies (affinity purification-mass spectrometry, directed binding assays) to identify partners, combined with structure-guided separation-of-function assays, would define the molecular activity.
Provenance (the field's own admissions):
Gap: It is unknown whether mug151 has a genuine, specific meiotic function or whether its classification as a "meiotically up-regulated gene" reflects only transcriptional induction of a broadly-acting nuclear protein.
OPEN BIOLOGY BP_DARK
What is known: The mug151 name and UniProt record connect it to meiotic up-regulation, and UniProt cites PMID:16303567 for a role in meiosis. The cached abstract reports a systematic screen of 175 meiotically up-regulated genes but does not identify mug151 or its outcome. The gap is therefore whether mug151 has a specific meiotic role and what evidence the full paper provides for that claim.
Significance: Distinguishing induced-expression from actual meiotic requirement is essential to avoid over-interpreting the "mug" designation as evidence of a meiotic role, and would either add mug151 to the catalog of meiotic factors or reassign it to a non-meiotic nuclear process.
What would resolve it: Detailed meiotic phenotyping of the deletion mutant (recombination, spore viability, chromosome segregation, meiotic progression), and identification of the pathway in which mug151 acts.
Provenance (the field's own admissions):
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