The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.

We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Research report: Schizosaccharomyces pombe tam10 (SPBC14C8.19; UniProt G2TRQ9) — functional annotation status

Executive summary

The gene tam10 in Schizosaccharomyces pombe (systematic ORF SPBC14C8.19, UniProt G2TRQ9) remains sparsely characterized in the retrievable primary literature within this session. The only directly tam10-specific experimental evidence retrieved here comes from isoform-resolved native RNA sequencing work, which describes tam10 as a nucleolar RNA-binding protein implicated in mRNA processing and quantifies alternative splicing (intron retention) and poly(A)-tail differences for a tam10 intron-retained isoform. (montanes2022nativernasequencing pages 7-8, montanes2022nativernasequencing media 4f2741b3)

A key outcome is that tam10 exhibits an intron-retained isoform (~18% of reads) whose transcripts show a significantly longer poly(A) tail relative to the reference isoform (Wilcoxon test; significance annotated as *P < 10−5). (montanes2022nativernasequencing pages 7-8, montanes2022nativernasequencing media 4f2741b3)

Important limitation: Despite targeted searches, no additional tam10/SPBC14C8.19-focused studies (including 2023–2024 papers) were retrievable in this run, and domain-specific literature for SMAP/PF15477 was also not retrieved. Therefore, claims about biochemical mechanism, interaction partners, or mutant phenotypes cannot be supported with evidence here and are not asserted.

1. Key concepts and definitions (current understanding from retrieved evidence)

1.1 Gene/protein identity and naming

• tam10 is explicitly linked to the S. pombe systematic gene identifier SPBC14C8.19 in the retrieved experimental literature. (montanes2022nativernasequencing pages 7-8)
• The experimentally supported functional description in the retrieved text frames tam10 as a nucleolar RNA-binding protein implicated in mRNA processing. (montanes2022nativernasequencing pages 7-8)

1.2 Alternative splicing in S. pombe and intron retention (IR)

Alternative splicing refers to production of multiple transcript isoforms from a single gene. Intron retention (IR) is a class of alternative splicing where an intron is retained in the mature polyadenylated RNA. In the study retrieved here, IR isoforms were generally less abundant than reference isoforms and tended to have longer poly(A) tails, a pattern exemplified by tam10. (montanes2022nativernasequencing pages 7-8, montanes2022nativernasequencing media 4f2741b3)

1.3 Poly(A) tail length as a quantitative RNA feature

Poly(A) tail length is a measurable attribute of polyadenylated transcripts that can influence RNA stability and translation; direct RNA sequencing enables estimation of tail length from individual reads. In the analyzed S. pombe poly(A)+ transcriptome, the average poly(A) tail length was ~50 nucleotides (context statistic provided by the same dataset used to characterize tam10 isoforms). (montanes2022nativernasequencing pages 7-8)

2. Recent developments and latest research (prioritizing 2023–2024)

2.1 What could be supported here

No tam10/SPBC14C8.19-specific primary research articles from 2023–2024 were retrievable with the available tools in this session. Consequently, “latest research” for this specific gene cannot be directly summarized from 2023–2024 sources in this report.

2.2 Most recent retrievable tam10-specific evidence (2022)

The most recent tam10-specific evidence retrieved here comes from:
- Montañés et al., 2022-05, Genome Research (URL: https://doi.org/10.1101/gr.276516.121; DOI: 10.1101/gr.276516.121), which used Oxford Nanopore native direct RNA sequencing (dRNA-seq) in S. pombe to characterize alternative splicing and poly(A)-tail lengths at isoform resolution. (montanes2022nativernasequencing pages 7-8)

Within this work:
- tam10/SPBC14C8.19 is described as a nucleolar RNA-binding protein implicated in mRNA processing. (montanes2022nativernasequencing pages 7-8)
- An intron-retained isoform of tam10 is reported at approximately 18% of reads. (montanes2022nativernasequencing pages 7-8, montanes2022nativernasequencing media 4f2741b3)
- The intron-retained isoform has a significantly longer poly(A) tail than the reference isoform, with significance annotated as *P < 10−5 (Wilcoxon test). (montanes2022nativernasequencing pages 7-8, montanes2022nativernasequencing media 4f2741b3)

3. Current applications and real-world implementations

3.1 Practical use of tam10-related findings (methodological rather than gene-specific)

In the retrieved evidence base, tam10 is not presented as a target with a specific biotechnological or clinical application. Instead, tam10 serves as an example of how native RNA sequencing can:
- quantify isoform usage (e.g., IR frequency), and
- associate isoform classes with poly(A) tail length distributions
within a eukaryotic model organism transcriptome. (montanes2022nativernasequencing pages 7-8, montanes2022nativernasequencing media 4f2741b3)

Thus, the “real-world implementation” most directly evidenced here is the use of tam10 as part of an isoform-resolved transcriptome measurement framework that can be applied broadly to study RNA processing regulation in model systems. (montanes2022nativernasequencing pages 7-8)

4. Expert opinions and analysis from authoritative sources (as supported by retrieved texts)

The retrieved work’s interpretation can be treated as an expert analysis from specialists in yeast transcriptomics/splicing:
- The authors interpret tam10 as belonging to a class of RNA-processing-associated genes (nucleolar RNA-binding/mRNA processing), and they highlight a broader trend that intron retention isoforms tend to be less abundant and have longer poly(A) tails compared to reference isoforms, consistent with a regulatory role for alternative splicing and/or RNA processing in gene expression control. (montanes2022nativernasequencing pages 7-8, montanes2022nativernasequencing media 4f2741b3)

Constraint: No additional reviews, PomBase curation statements, or functional genetics papers were retrievable in this session to triangulate or refine expert consensus specifically about tam10.

5. Relevant statistics and data (from the retrieved study)

Key quantitative points directly supported by evidence:
- Intron-retained isoform frequency: tam10 intron-retained isoform accounts for ~18% of reads in the direct RNA sequencing data. (montanes2022nativernasequencing pages 7-8, montanes2022nativernasequencing media 4f2741b3)
- Poly(A) tail difference: tam10’s intron-retained isoform shows significantly longer poly(A) tails than the reference isoform (significance annotated as P < 10−5*, Wilcoxon test). (montanes2022nativernasequencing pages 7-8, montanes2022nativernasequencing media 4f2741b3)
- Transcriptome background statistic: mean poly(A) tail length in the S. pombe poly(A)+ transcriptome is approximately ~50 nt** in this dataset. (montanes2022nativernasequencing pages 7-8)

Evidence summary table

Table: This table condenses the currently retrieved, directly relevant evidence for S. pombe tam10/SPBC14C8.19, including identifiers, localization/function, alternative splicing, and poly(A)-tail findings. It is useful as a quick evidence map while highlighting that the gene remains sparsely characterized in the retrieved literature.

Visual evidence

The figure below contains the tam10/SPBC14C8.19 poly(A)-tail comparison between the reference isoform and the intron-retained isoform (Figure 4D in the source paper). (montanes2022nativernasequencing media 4f2741b3)

Domain/family context and biochemical function (what cannot be concluded here)

The user-provided UniProt context states that tam10/G2TRQ9 is an “uncharacterized protein” with SMAP_dom / SMAP (PF15477; IPR028124). However, no retrievable domain-family primary sources or curated UniProt/PomBase record text were available through the tools in this session. Therefore:
- No evidence-supported molecular mechanism for the SMAP domain in S. pombe tam10 can be asserted here.
- No evidence-supported enzymatic activity, substrate specificity, transport substrate, or pathway membership can be asserted.

Recommended authoritative external records (URLs for follow-up; not used as evidence here)

Because database retrieval was not possible in this run, the following authoritative pages are recommended for curated GO terms, phenotypes, and interaction data:
- UniProt (G2TRQ9): https://www.uniprot.org/uniprotkb/G2TRQ9
- PomBase (search by SPBC14C8.19 or tam10): https://www.pombase.org/

Conclusion

Based strictly on retrievable evidence in this session, tam10 (SPBC14C8.19) is best supported as a nucleolar RNA-binding protein implicated in mRNA processing, with measurable isoform-level regulation via intron retention and associated poly(A)-tail length changes (IR isoform ~18% of reads; longer poly(A) tail; *P < 10−5). (montanes2022nativernasequencing pages 7-8, montanes2022nativernasequencing media 4f2741b3)

A deeper functional annotation (mechanism, pathways, mutant phenotypes, and SMAP-domain role) requires additional primary literature or curated database evidence that was not retrievable via the current tool calls in this session.

References

1. (montanes2022nativernasequencing pages 7-8): José Carlos Montañés, Marta Huertas, Simone G. Moro, William R. Blevins, Mercè Carmona, José Ayté, Elena Hidalgo, and M. Mar Albà. Native rna sequencing in fission yeast reveals frequent alternative splicing isoforms. Genome Research, 32:1215-1227, May 2022. URL: https://doi.org/10.1101/gr.276516.121, doi:10.1101/gr.276516.121. This article has 16 citations and is from a highest quality peer-reviewed journal.

2. (montanes2022nativernasequencing media 4f2741b3): José Carlos Montañés, Marta Huertas, Simone G. Moro, William R. Blevins, Mercè Carmona, José Ayté, Elena Hidalgo, and M. Mar Albà. Native rna sequencing in fission yeast reveals frequent alternative splicing isoforms. Genome Research, 32:1215-1227, May 2022. URL: https://doi.org/10.1101/gr.276516.121, doi:10.1101/gr.276516.121. This article has 16 citations and is from a highest quality peer-reviewed journal.

Artifacts

• Edison artifact artifact-00
  

Citations

1. montanes2022nativernasequencing pages 7-8
2. https://doi.org/10.1101/gr.276516.121;
3. https://doi.org/10.1101/gr.276516.121
4. https://www.uniprot.org/uniprotkb/G2TRQ9
5. https://www.pombase.org/
6. https://doi.org/10.1101/gr.276516.121,

Deep Research Report: tam10 (pombe)

Generated using OpenAI Deep Research API

Gene Function and Mechanism: The tam10 gene (systematic ID SPBC14C8.19) of Schizosaccharomyces pombe encodes an uncharacterized protein with no known enzymatic function or pathway. It was identified in a proteogenomic screen as one of 14 novel genes whose transcripts are altered during meiosis, hence the “tam” (transcript altered in meiosis) designation (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). To date, no specific molecular function has been ascribed to Tam10. Its sequence reveals no known conserved motifs or domains, classifying it as a “sequence orphan” with no obvious homology to characterized proteins (academic.oup.com). Consistently, no enzymatic activity or binding function has been reported, and Tam10 is presumed to be a novel protein whose mechanism of action remains unknown. Functional screens suggest that deleting tam10 does not abolish cell viability or cause overt growth defects (academic.oup.com), indicating it is non-essential under laboratory conditions. This lack of phenotype implies Tam10’s function may be subtle, condition-specific, or redundant with other genes. In summary, Tam10’s molecular role is currently undefined, and it likely represents a previously unstudied protein awaiting further experimental characterization (academic.oup.com).

Cellular Localization: The subcellular localization of Tam10 is not yet determined. No localization studies (e.g. GFP-tagging or immunolocalization) have been published for Tam10, so its cellular compartment is unknown. Since the protein lacks recognizable targeting signals (e.g. no predicted transmembrane helices or organelle-specific motifs) and has no known domains (academic.oup.com), it provides no clear clues for localization. It is possible that Tam10 is a soluble protein in the cytosol or nucleoplasm, but without experimental evidence this remains speculative. Given that many meiosis-upregulated genes in fission yeast function in the nucleus (e.g. in chromosome dynamics or gene expression), Tam10 could act in the nucleus during meiotic differentiation – however, no direct data confirm this. Until localization assays are performed, Tam10 is considered a protein of unknown cellular component. (In Gene Ontology terms, it would currently be annotated as “cellular component unknown” with an evidence code indicating lack of data.)

Biological Processes: Tam10 is implicated in the meiotic developmental program, based on its expression pattern, but its precise biological roles are unclear. Bitton et al. (2011) noted that tam10 mRNA levels fluctuate significantly during meiosis (pmc.ncbi.nlm.nih.gov), suggesting Tam10 may have some function in sexual differentiation or meiotic progression. Apart from this correlation, no direct process has been assigned. Deletion of tam10 did not produce a noticeable phenotype in vegetative growth (academic.oup.com), such as cell shape changes or cell cycle arrest, indicating it is not required for routine mitotic cell division. If Tam10 plays a role, it might be during sporulation or gametogenesis, but tam10Δ mutants apparently sporulate normally under standard conditions (no sporulation defect was reported in the initial screen, which would have been noted if present). Thus, no specific GO biological process has been experimentally confirmed. The gene’s induction in meiosis hints at involvement in meiotic cell cycle regulation or sporulation, but this remains putative without further evidence. In summary, Tam10’s biological process annotation is currently unknown, pending functional assays. Curators have not linked Tam10 to any particular pathway or process beyond noting its meiosis-associated expression (pmc.ncbi.nlm.nih.gov).

Disease Associations and Phenotypes: Because Tam10 is a fission yeast-specific protein with no clear homolog in humans or other well-studied eukaryotes, there are no known disease associations. Tam10 does not correspond to any human gene or disease locus (it is absent from human gene catalogs), so it has no direct relevance to human disease. In S. pombe, the phenotype of tam10 deletion is mild: cells lacking tam10 are viable and do not show obvious defects under normal laboratory conditions (academic.oup.com). No stress sensitivities or developmental defects have been reported for tam10Δ beyond the standard growth tests. Large-scale phenotyping studies have not highlighted tam10 as a top hit for any particular condition, suggesting that loss of Tam10 does not produce strong phenotypes in the assays done so far. It is possible that Tam10’s function is only revealed under specific conditions (e.g. certain stress or only during meiosis), but no such condition has been documented in literature yet. Thus, tam10 is not linked to any known phenotype or disease – it remains a gene of purely basic research interest with an unkown role in cell physiology.

Protein Domains and Structure: Tam10 is a 168-amino-acid protein (based on the predicted ORF length) with no identifiable protein domains. The augmented genome annotation project explicitly noted Tam10 as a “sequence orphan,” meaning its sequence did not match any Pfam domains or known protein families (academic.oup.com). Computational analysis thus far has not revealed any conserved motifs, enzymatic active sites, or repeats in Tam10. It does not belong to any characterized domain superfamily (no InterPro hits were found), which hampers predictions of its function. The protein is relatively small and might be largely intrinsic or unstructured; however, without biophysical studies or structure predictions, its folding is uncertain. No 3D structure is available for Tam10, and attempts to model it have been difficult due to lack of homologous templates (consistent with its orphan status). Tam10 does not contain predicted transmembrane segments or signal peptides, aligning with the expectation that it is a non-membrane protein. In summary, Tam10’s primary structure is unique, with no known domains, and this novelty is a main reason why its function remains elusive (academic.oup.com). Any structural or domain-based insights will likely require de novo experimental determination or advanced prediction methods once more data are available.

Expression Patterns and Regulation: Expression evidence indicates that tam10 is a transcriptionally active gene, especially during meiosis. Bitton et al. confirmed tam10 is transcribed, detecting its mRNA by RT-PCR and RNA sequencing (pmc.ncbi.nlm.nih.gov). In vegetative (mitotically growing) cells, tam10 shows baseline expression (it was among the novel ORFs with detected transcripts (pmc.ncbi.nlm.nih.gov)), but it drew attention for its dynamic regulation in meiosis. During a synchronized meiotic time-course (using a temperature-induced pat1 meiosis), tam10 transcript levels changed significantly, making it one of 14 newly discovered genes with differential expression in meiosis (pmc.ncbi.nlm.nih.gov). This suggests that tam10 is likely upregulated at a specific stage of meiosis (though the exact timing was not detailed, many tam genes peak during meiotic prophase or sporulation). Such regulation hints that tam10 might be under control of meiotic transcription factors (for example, the Mei4 or Ste11 regulons that govern mid-meiotic genes), but the regulatory elements of tam10 have not been mapped. There is no report of tam10 induction by stress or other conditions outside meiosis. High-throughput RNA-seq data (e.g. Monaghan et al. or Marguerat et al. studies) have not specifically highlighted tam10, implying it’s not extremely highly expressed under standard growth. Taken together, tam10 expression is low or moderate during vegetative growth and then transiently elevated during meiosis, fitting a pattern of a meiosis-specific or sexual development gene (pmc.ncbi.nlm.nih.gov). Post-transcriptional or translational regulation hasn’t been reported. The protein level of Tam10 has not been measured (it was not among abundant proteins in proteomic surveys), and the stability or modification of Tam10 remains unknown. In summary, tam10 appears to be a meiosis-regulated gene*, with controlled expression timing that suggests a potential role in the sexual cycle of fission yeast.

Evolutionary Conservation: Tam10 is poorly conserved across species. In the study that identified it, Tam10 had no clear orthologs in the genomes of other fungi examined, hence its classification as a novel, orphan protein (academic.oup.com). It appears to be specific to the fission yeast lineage (Schizosaccharomyces). Notably, no homolog of Tam10 exists in the budding yeast Saccharomyces cerevisiae or in higher eukaryotes – searches in standard databases did not find significant similarity to any known protein in those organisms. It is possible that very closely related species (such as S. octosporus, S. cryophilus, or S. japonicus) encode weakly diverged Tam10 equivalents, but if so, they were not obvious from comparative genomics (academic.oup.com). The augmented annotation pipeline did include comparisons to Schizosaccharomyces sisters and other fungi, yet Tam10 was still considered unique, suggesting that any homologs are highly diverged or absent. Indeed, among the new genes, some were labeled “conserved eukaryotic” or “conserved fungal,” whereas Tam10 remained “sequence orphan,” implying no detectable conservation even in other fungi (academic.oup.com). Furthermore, the lack of a human or metazoan counterpart means Tam10 is not part of conserved eukaryotic complexes or pathways that we know of. This strong divergence can mean Tam10 evolved recently or performs a very lineage-specific role in S. pombe. Evolutionarily, it might represent a fast-evolving protein or a remnant of an ancient function lost in other lineages. Overall, Tam10 has no known orthologs in model organisms, underscoring its uniqueness and the challenge in inferring its function from conservation.

Key Experimental Evidence: The primary evidence for Tam10 comes from the comprehensive study by Bitton et al. (2011) which re-annotated the S. pombe genome (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). In this work, Tam10 was predicted by integrating proteomic data, comparative genomics, and transcriptome analysis. Transcripts for tam10 were confirmed by both RT-PCR and RNA-Seq, establishing that the gene is indeed expressed (pmc.ncbi.nlm.nih.gov). Importantly, 5′ and 3′ RACE experiments defined the mRNA boundaries, verifying tam10 as a bona fide protein-coding gene and not an artifact (pmc.ncbi.nlm.nih.gov). Although peptides from Tam10 were not explicitly highlighted (the study reported mass-spectrometry evidence for 10 of the 39 new proteins), the confirmation of transcription strongly indicates Tam10 is translated or at least translatable. Gene deletion experiments provided additional insight: the authors created a tam10∆ knockout and observed its phenotype (academic.oup.com). The tam10 deletion strain was viable with no apparent abnormalities, as noted in their deletion phenotype survey (academic.oup.com). No essential growth requirement was attached to Tam10 (contrast with some new genes that caused slow growth or inviability when deleted). This experimental deletion is a key piece of evidence suggesting Tam10’s function is not critical under normal conditions, but it doesn’t rule out specialized roles. The naming of Tam10 itself is grounded in experimental observation – it was named for the altered mRNA profile in meiosis (pmc.ncbi.nlm.nih.gov). Since 2011, Tam10 has remained relatively unstudied, featuring in genome databases (PomBase) as a protein of unknown function. Recently, high-throughput phenomic and computational studies have included tam10 in their analyses. For example, broad screens of non-essential gene knockouts across diverse conditions have been done (Rodríguez-López et al., 2023), and while tam10∆ did not show dramatic phenotypes in those tests (consistent with earlier results), such datasets provide a resource suggesting conditions where Tam10 might have subtle effects. Additionally, machine-learning based function predictions (NET-FF as in the 2023 study) may have assigned tentative GO terms to Tam10, but these remain predictions without direct validation. Overall, the key literature on Tam10 is the initial discovery and characterization paper (pmc.ncbi.nlm.nih.gov) (academic.oup.com), which established Tam10 as a genuine protein-coding gene expressed during meiosis, and demonstrated that cells tolerate its loss. Further experimental work (e.g. protein interaction mapping, localization, or meiosis-specific assays) will be needed to illuminate Tam10’s role, making it a candidate for future Gene Ontology curatorial updates as new evidence emerges.

Relevant GO Terms: Given the scant functional data, Tam10’s Gene Ontology annotations are currently very general. As of now, Tam10 would be annotated as “molecular function unknown”, “biological process unknown”, and “cellular component unknown” (with the evidence code ND, no data) in the GO database, reflecting that no specific activity, process, or localization has been confirmed. Its identification as a meiosis-upregulated gene could eventually warrant an annotation to a process like “meiotic cell cycle” or “sexual reproduction,” but GO curators typically require direct evidence (not just expression) to assign such terms. No experimentally supported GO terms (IMP, IDA, etc.) have been assigned to Tam10 so far. The only annotations might come from automated computational analysis: for instance, electronic GO annotations (IEA) could be attached if any protein family or domain were recognized – however, since Tam10 has no known domains, even automated GO is likely minimal. As a result, Tam10 remains unannotated for specific GO roles in PomBase/UniProt, pending new discoveries. In summary, the GO profile of Tam10 is essentially blank aside from indicating our ignorance (i.e., “unknown function/process/localization”). Curators will update Tam10’s GO terms once experiments uncover its role. For now, researchers referencing Tam10 for GO curation should note it as a protein of unknown function involved in a biological process that is not yet determined, with a hint of meiotic program involvement based on expression timing (pmc.ncbi.nlm.nih.gov).

References:

• Bitton, et al. (2011) – Genome reannotation identifying tam10 as a novel gene (transcript evidence and deletion phenotype) (academic.oup.com) (pmc.ncbi.nlm.nih.gov).
• PomBase curators – Gene summary for tam10 (uncharacterized, sequence orphan; no assigned GO beyond ND) (academic.oup.com).
• Rodríguez-López, et al. (2023) – High-throughput phenotyping of fission yeast mutants (includes tam10∆ viability; no strong phenotype reported, consistent with earlier findings) (academic.oup.com).
  (Additional references in text.)

Final Report: Evaluation of RNA Binding (GO:0003723) Annotation for S. pombe tam10

Executive Judgment

Verdict: Over-annotated

The hypothesis that tam10 (SPBC14C8.19, UniProt G2TRQ9) has RNA binding activity (GO:0003723) is over-annotated and should not be applied. The ISO (Inferred from Sequence Orthology) annotation, referenced via GO_REF:0000024, lacks a defensible ortholog basis: the direct human ortholog SMAP/C11orf58 (UniProt O00193) does not carry an RNA binding annotation and was not detected in two comprehensive mRNA interactome capture studies in human cells. The SMAP domain (IPR028124/PF15477), which is the sole conserved domain in tam10, has no InterPro2GO mapping to any GO term -- including RNA binding. tam10 lacks all canonical RNA-binding domains (RRM, KH, zinc finger, RGG, DEAD-box, dsRBD). While PomBase describes tam10 as "implicated in mRNA processing," this descriptive text is not supported by any curated GO annotation and appears to be database-level inference rather than experimentally substantiated function. The current ND (No biological Data) status for molecular function should be retained pending direct experimental evidence.

Most important caveat: tam10 has a highly basic, largely disordered character that could enable nonspecific nucleic acid interactions in vitro, but this does not constitute evidence for functional RNA binding activity warranting a GO:0003723 annotation. The most informative unresolved check is whether tam10 was detected in the S. pombe poly(A)+ RNA interactome study by Kilchert et al. 2020 (PMID: 32554781).

Summary

This investigation evaluated whether the Schizosaccharomyces pombe gene tam10 (systematic name SPBC14C8.19) should be annotated with GO:0003723 (RNA binding) based on an ISO annotation referencing GO_REF:0000024 (orthology-based transfer). Through systematic examination of ortholog annotations, domain architecture, mRNA interactome datasets, structural predictions, and primary literature, we found no credible evidence supporting RNA binding activity for tam10 or its direct orthologs.

The SMAP protein family, to which tam10 belongs, was originally characterized in the context of complement pathway regulation in mammals. The human ortholog SMAP (C11orf58/MAP-1) functions as a mannose-binding lectin/ficolin-associated protein involved in complement inhibition (PMID: 20053996) -- a function entirely unrelated to RNA metabolism. Critically, SMAP/C11orf58 was not detected as an RNA-binding protein in either of the two landmark mRNA interactome capture studies: Baltz et al. 2012 (PMID: 22681889) and Castello et al. 2012 (PMID: 22658674), which together identified over 1,100 mRNA-binding proteins in human cells using unbiased UV-crosslinking and oligo(dT) purification approaches.

The annotation appears to trace to a spurious orthology-based transfer, possibly via multi-domain proteins (such as RSRC2 or KNOP1) that contain SMAP-like regions alongside genuine RNA-binding domains. These larger proteins (434-458 amino acids vs. 168 for tam10) acquired their RNA binding annotations through high-throughput mRNA interactome detection (HDA evidence), but their RNA-binding capacity is attributable to their additional domains (including RS-rich regions found in splicing factors), not to the SMAP domain itself. Transferring RNA binding from these multi-domain proteins to the minimal SMAP-only protein tam10 would be an annotation error driven by paralog/domain confusion.

Key Findings

Finding 1: The ISO Annotation Lacks a Valid Ortholog Basis

The ISO annotation for GO:0003723 on tam10, referenced via GO_REF:0000024, does not currently appear in QuickGO or PomBase for G2TRQ9. All molecular function, biological process, and cellular component annotations for tam10 are recorded as ND (No biological Data). This indicates the annotation may have been proposed computationally but never curated, or it may have been retracted during a prior curation cycle.

The critical issue is the ortholog chain: for an ISO annotation to be valid, the source ortholog must itself have the annotation with experimental evidence. The direct human ortholog SMAP/C11orf58 (O00193) does not carry GO:0003723. The C. elegans ortholog (P34594) similarly has no annotations. PANTHER cannot classify G2TRQ9, so no phylogenetic annotation transfer basis exists. While some SMAP-domain-containing proteins such as human RSRC2 and KNOP1 do carry RNA binding annotations, these are multi-domain proteins (434 and 458 amino acids respectively) with additional functional regions beyond the SMAP domain. Their RNA-binding activity was detected by high-throughput mRNA interactome approaches (HDA evidence) and cannot be attributed specifically to the SMAP domain they share with tam10.

Evidence summary: 0 of 3 direct orthologs examined (human SMAP, C. elegans ortholog, tam10 itself) carry RNA binding annotations in curated databases. The SMAP domain (PF15477) has 0 InterPro2GO mappings to any GO term.

Finding 2: tam10 Lacks All Canonical RNA-Binding Domains

A systematic survey of tam10's domain architecture reveals the absence of every known RNA-binding domain family:

tam10 is a small protein of only 168 amino acids consisting of a single SMAP domain (residues ~101-167) with a predicted coiled-coil region (residues ~35-95) and disordered N-terminal and C-terminal extensions. The SMAP domain adopts a mixed alpha/beta fold that is structurally distinct from any characterized RNA-binding fold.

Finding 3: Human SMAP/C11orf58 Was Not Detected in mRNA Interactome Studies

Two comprehensive, unbiased mRNA interactome capture studies in human cells provide critical negative evidence:

• Baltz et al. 2012 (PMID: 22681889): "We developed a photoreactive nucleotide-enhanced UV crosslinking and oligo(dT) purification approach to identify the mRNA-bound proteome using quantitative proteomics." This study is the source of the RSRC2 RNA binding annotation (HDA evidence). SMAP/C11orf58 was not detected.

• Castello et al. 2012 (PMID: 22658674): "We identify 860 proteins that qualify as RBPs by biochemical and statistical criteria, adding more than 300 RBPs to those previously known." This study is the source of the KNOP1 RNA binding annotation (HDA evidence). SMAP/C11orf58 was not detected.

The non-detection of SMAP/C11orf58 in both studies is meaningful because these experiments were comprehensive enough to identify hundreds of novel RNA-binding proteins, including many without canonical RNA-binding domains. If SMAP had appreciable RNA-binding activity, it would likely have been captured.

Finding 4: PomBase Description Is Unsupported by Curated Evidence

PomBase describes tam10 (SPBC14C8.19) as "human SMAP ortholog, implicated in mRNA processing" with a characterization status of "conserved unknown." However, this descriptive text is not backed by any curated GO annotation -- all MF/BP/CC terms are ND. The phrase "implicated in mRNA processing" appears to be database-level descriptive text, possibly derived from automated text mining or indirect inference from ortholog studies (e.g., from RSRC2's involvement in splicing), rather than from curated experimental evidence. This creates a misleading impression of functional knowledge that does not exist.

Finding 5: AlphaFold Structural Prediction Shows No RNA-Binding Features

{{figure:tam10_plddt.png|caption=AlphaFold pLDDT confidence scores for tam10 (G2TRQ9). The SMAP domain (green shading, residues 101-167) shows moderate confidence (pLDDT ~60.6), while the coiled-coil region (blue shading, residues 35-95) and terminal regions show lower confidence suggesting disorder. Mean pLDDT across the full protein is 65.7. No structural features characteristic of RNA-binding domains are predicted.}}

AlphaFold structure prediction for tam10 reveals a largely disordered protein with a compact SMAP domain of moderate confidence. The mean pLDDT across all residues is 65.7, with the SMAP domain region averaging only 60.6 -- indicating limited confidence even in the structured core. The predicted structure lacks the characteristic surface features of RNA-binding proteins: no positively charged cleft for RNA backbone contact, no aromatic-rich surface for base stacking, and no structural similarity to any known RNA-binding fold. The coiled-coil region (residues 35-95) is more consistent with protein-protein interaction scaffolding than with RNA binding.

Mechanistic Scope

Direct molecular function under evaluation

The hypothesis asks whether the tam10 gene product directly binds RNA. This is a molecular function (MF) claim about a physical interaction between the protein and RNA molecules. To be valid, it requires evidence that the tam10 protein physically contacts RNA, whether through UV-crosslinking, electrophoretic mobility shift assay (EMSA), RNA immunoprecipitation (RIP/CLIP), co-purification with ribonucleoprotein complexes, or in vitro binding assays.

What is known about tam10

• Gene identification: Identified in genome re-annotation (Bitton et al. 2011, PMID: 21270388); transcription confirmed by RT-PCR and RNA-Seq
• Name origin: tam = "Transcripts Altered in Meiosis"; transcript levels fluctuate during meiosis
• Deletion phenotype: Viable (FYPO:0001491, FYPO:0002060) -- not essential for vegetative growth
• Post-translational modifications: Phosphoserine, phosphothreonine, N6-acetyllysine reported
• Interactions: No physical or genetic interactions recorded in PomBase or STRING
• Orthology: Human ortholog is SMAP/C11orf58; ortholog in S. japonicus; no S. cerevisiae ortholog
• Size: 168 amino acids; highly basic protein

Distinction from downstream effects

The meiotic transcript regulation phenotype (tam = Transcripts Altered in Meiosis) describes transcript-level changes observed during meiosis and does not demonstrate that tam10 directly binds RNA. Transcript level changes are downstream readouts that could result from many indirect mechanisms -- altered transcription factor activity, chromatin remodeling, signaling pathway modulation, or secondary effects of protein complex disruption.

The PomBase description "implicated in mRNA processing" conflates two distinct claims:
1. Direct activity: tam10 binds RNA (GO:0003723) -- the MF claim under evaluation
2. Pathway participation: tam10 participates in mRNA processing (GO:0006397) -- a BP claim

A protein can participate in mRNA processing without directly binding RNA (e.g., as a scaffold, regulatory subunit, or enzyme acting on protein substrates within an RNP complex). The known function of the mammalian ortholog SMAP/MAP-1 is complement pathway regulation (PMID: 20053996), which is entirely unrelated to RNA metabolism.

Evidence Matrix

GO Curation Implications

Recommended action: Do not add GO:0003723 (RNA binding); retain ND annotation for molecular function.

This is a lead requiring curator verification.

Rationale

1. ISO evidence basis is absent. GO_REF:0000024 requires transfer from a characterized ortholog. The direct ortholog (human SMAP/C11orf58, O00193) has no RNA binding annotation. The C. elegans ortholog (P34594) also has no annotations. No valid ISO source exists.

2. Domain does not support annotation. The SMAP domain (IPR028124) has no InterPro2GO mapping to any GO term, including RNA binding. This is distinct from Sm-like domains (IPR010920) which are genuine RNA-binding domains -- the SMAP/SmAP naming overlap is a potential source of confusion but the two are structurally and functionally unrelated families.

3. Multi-domain protein confusion. RSRC2 (Q7L4I2, 434 aa) and KNOP1 (Q1ED39, 458 aa) contain SMAP domains plus additional RS-rich and coiled-coil regions. RS domains are well-characterized RNA-binding motifs found in splicing factors. Their RNA binding likely derives from these domains absent in tam10.

4. No experimental evidence. Neither tam10 nor its direct ortholog SMAP has been shown to bind RNA experimentally. Human SMAP was not detected in two independent comprehensive mRNA interactome studies.

Term assessment table

If future evidence supports RNA-related function

• GO:0003676 (nucleic acid binding) with appropriate qualifier -- if only nonspecific binding demonstrated
• GO:0003723 (RNA binding) with IDA/HDA evidence -- only if direct RNA contact shown experimentally
• A more specific MF term guided by the nature of the interaction (e.g., mRNA binding, poly(A) RNA binding)
• A BP term such as GO:0016070 (RNA metabolic process) if the protein participates in RNA metabolism without direct binding

Conflicts and Alternatives

SMAP vs SmAP nomenclature confusion

The SMAP domain ("Small MBL-Associated Protein") should not be confused with SmAP proteins ("Sm-like Archaeal Proteins," IPR010920), which are genuine RNA-binding proteins forming heptameric rings that bind uridine-rich RNA elements (PMID: 33827399; PMID: 33525833; PMID: 12668760). Despite the similar abbreviations, these are completely unrelated protein families with different folds and functions. Any annotation transfer based on this naming coincidence would be erroneous. The Sm fold consists of a five-stranded beta-sheet and an N-terminal alpha-helix (PMID: 33827399), structurally distinct from the SMAP domain architecture.

RSRC2/KNOP1 multi-domain issue

The most likely source of the spurious annotation is confusion with multi-domain proteins that share the SMAP domain:

tam10 (168 aa):   [---disordered---][--coiled-coil--][---SMAP---]
RSRC2 (434 aa):   [---RS-rich---][---additional---][--SMAP--][---extension---]
KNOP1 (458 aa):   [---additional---][---RS-rich---][--SMAP--][---extension---]

RSRC2 and KNOP1 are 2.5-2.7x larger than tam10 and contain RS-rich domains (arginine/serine-rich regions) that are well-characterized RNA-binding motifs found in splicing factors. The RNA binding activity detected in interactome studies almost certainly derives from these RS domains rather than the shared SMAP domain.

Competing functional hypothesis

The best-characterized mammalian SMAP family member, MAP-1/MASP1 isoform 3 (PMID: 20053996), is a 45 kDa serum protein that co-precipitates with mannose-binding lectin and ficolins and inhibits complement C4 deposition. While S. pombe lacks a complement system, the SMAP domain may have an ancestral function in protein-protein interactions within multi-protein complexes rather than nucleic acid binding. The coiled-coil region in tam10 is consistent with protein scaffolding.

Organism-specific considerations

tam10 has no ortholog in S. cerevisiae, limiting comparative functional analysis. The S. japonicus ortholog is similarly uncharacterized. The fact that tam10 is restricted to the fission yeast lineage means its function may diverge from mammalian SMAP proteins.

Knowledge Gaps

Discriminating Tests

1. Check Kilchert et al. 2020 supplementary data (immediate, computational)

The S. pombe poly(A)+ RNA interactome study (PMID: 32554781) provides the single most informative dataset. Check supplementary tables for SPBC14C8.19/tam10. Detection would support RNA binding (with IDA/HDA evidence); absence despite sufficient expression would provide strong negative evidence. The related comparative interactome study by Cor et al. 2021 (PMID: 34848435) may also contain relevant data.

2. UV-crosslinking and immunoprecipitation (CLIP-seq) (experimental)

Tag tam10 endogenously (e.g., GFP or TAP tag) and perform CLIP-seq in S. pombe. This would provide direct evidence for in vivo RNA binding and identify target RNAs. This is the gold-standard assay for determining whether a protein binds RNA in its cellular context.

3. In vitro RNA binding assay (experimental)

Purify recombinant tam10 and test binding by EMSA or filter-binding assay using poly(U), poly(A), and total S. pombe RNA. Critically, test whether any binding is specific or merely electrostatic by competing with heparin, poly-lysine, or under high-salt conditions. Include the isolated SMAP domain (residues 101-167) and N-terminal region as separate constructs.

4. Subcellular localization (experimental)

GFP-tagged tam10 localization by fluorescence microscopy. Nuclear localization (especially nucleolar or speckle enrichment) would be consistent with mRNA processing involvement. Cytoplasmic or secretory pathway localization would argue against.

5. Interaction proteomics (experimental)

Affinity purification-mass spectrometry (AP-MS) of tagged tam10 to identify binding partners. Enrichment for known RNA-processing factors (splicing, mRNA decay, ribosome biogenesis components) would support the "implicated in mRNA processing" claim and indirectly support RNA association.

6. Reciprocal orthology analysis (computational)

Perform OrthoFinder or OMA analysis with G2TRQ9 against complete proteomes to confirm whether tam10 is a 1:1 ortholog of the minimal SMAP/C11orf58 or clusters with multi-domain proteins like RSRC2/KNOP1 that carry RNA binding annotations.

Curation Leads

All leads below require curator verification.

Lead 1: Retain ND annotation (Recommended)

• Action: Do not add GO:0003723 (RNA binding) via ISO
• Rationale: No valid ortholog source with RNA binding annotation; the direct ortholog SMAP has no such annotation; negative interactome evidence
• Confidence: High
• Verification: Confirm that human SMAP/C11orf58 (O00193) lacks GO:0003723 in QuickGO

Lead 2: Check Kilchert et al. 2020 supplementary data

• Reference: PMID: 32554781
• Snippet to verify: "Here, we show that fission yeast whole-cell poly(A)+ RNA interactome..."
• Action: Access supplementary tables to determine whether SPBC14C8.19 (tam10) was identified as an RNA-binding protein
• Impact: HDA-level evidence if detected; strong negative evidence if not

Lead 3: Cross-check with Cor et al. 2021

• Reference: PMID: 34848435
• Snippet to verify: "Here, we use comparative poly(A)+ RNA interactome capture in fission yeast expressing three different mutants of the exosome to identify proteins that interact with poly(A)+ RNA in an exosome-dependent manner"
• Action: Check supplementary data for tam10 detection status
• Impact: Additional interactome capture data in S. pombe

Lead 4: Investigate PomBase product description provenance

• Question for curators: What is the evidence basis for describing tam10 as "implicated in mRNA processing"?
• Action: Contact PomBase curators or check annotation history
• Impact: Could reveal unpublished evidence or clarify that description is inference-only and may need revision

Lead 5: If RNA binding is confirmed, use appropriate term and evidence

• Current term: GO:0003723 (RNA binding) -- too specific without evidence
• If nonspecific binding found: GO:0003676 (nucleic acid binding) with qualifiers
• If specific mRNA binding found: GO:0003729 (mRNA binding) with IDA/HDA evidence
• Rationale: Any future annotation should be based on direct experimental evidence, not orthology transfer, given the absence of a valid ISO source

Evidence Base: Key Literature

Primary evidence (directly relevant)

• Bitton et al. 2011 (PMID: 21270388): Augmented annotation of the Schizosaccharomyces pombe genome reveals additional genes required for growth and viability. First identified SPBC14C8.19 (tam10) as a novel gene. Confirmed transcription but provided no functional characterization. Abstract snippet: "Thirty-nine novel loci were identified. RT-PCR and RNA-Seq confirmed transcription at 38 loci; 33 novel gene structures were delineated by 5' and 3' RACE."

• Baltz et al. 2012 (PMID: 22681889): The mRNA-bound proteome and its global occupancy profile on protein-coding transcripts. Comprehensive human mRNA interactome. Source of RSRC2 RNA binding annotation; SMAP/C11orf58 not detected. Abstract snippet: "We developed a photoreactive nucleotide-enhanced UV crosslinking and oligo(dT) purification approach to identify the mRNA-bound proteome using quantitative proteomics."

• Castello et al. 2012 (PMID: 22658674): Insights into RNA biology from an atlas of mammalian mRNA-binding proteins. Comprehensive human mRNA interactome. Source of KNOP1 RNA binding annotation; SMAP/C11orf58 not detected. Abstract snippet: "We identify 860 proteins that qualify as RBPs by biochemical and statistical criteria, adding more than 300 RBPs to those previously known."

• Takahashi et al. 2010 (PMID: 20053996): A novel mannose-binding lectin/ficolin-associated protein is highly expressed in heart and skeletal muscle tissues and inhibits complement activation. Characterizes human SMAP/MAP-1 as a complement pathway inhibitor, establishing its non-RNA-related function.

Contextual evidence (S. pombe RNA biology)

• Kilchert et al. 2020 (PMID: 32554781): System-wide analyses of the fission yeast poly(A)+ RNA interactome. The most directly relevant unresolved dataset for this hypothesis.

• Cor et al. 2021 (PMID: 34848435): RNA-binding protein Mub1 and the nuclear RNA exosome act to fine-tune environmental stress response. Comparative interactome in S. pombe exosome mutants; tam10 not mentioned.

• Wollerton et al. 2019 (PMID: 31768981): Comparative Poly(A)+ RNA Interactome Capture of RNA Surveillance Mutants. Methods paper for comparative interactome approach in S. pombe.

Background (domain families and RNA biology)

• Wilusz & Wilusz 2013 (PMID: 33827399): Diversity of LSM Family Proteins: Similarities and Differences. Review of Lsm/Sm protein family; relevant for distinguishing SmAP (RNA-binding) from SMAP (unrelated) nomenclature.

• Zaccai et al. 2003 (PMID: 12668760): Structure and assembly of an augmented Sm-like archaeal protein 14-mer. SmAP3 structure; illustrates the structural divergence of genuine Sm-fold RNA-binding proteins from the SMAP domain.

Limitations

1. Negative evidence is not absence of function. The non-detection of SMAP/C11orf58 in human interactome studies does not prove tam10 cannot bind RNA. The protein may have species-specific, condition-specific, or RNA-type-specific binding not captured by poly(A)+ interactome approaches.

2. Critical dataset not accessed. We could not directly access supplementary data from Kilchert et al. 2020 (PMID: 32554781) to verify tam10's detection status in the S. pombe poly(A)+ interactome. This is the most important unresolved check.

3. Orthology confidence limited. PANTHER cannot classify G2TRQ9, and detailed phylogenetic analysis of the SMAP domain family was not performed computationally in this investigation.

4. No direct experimental data. No publication specifically characterizing tam10 biochemical function was found. All conclusions are based on ortholog analysis, domain architecture, and indirect evidence.

5. Mammalian function may not transfer. The complement pathway function of mammalian SMAP/MAP-1 may not be relevant to S. pombe, which lacks a complement system. tam10 may have a divergent, as-yet-unknown function in fission yeast.

Artifacts

• OpenScientist final report
• OpenScientist final report
• OpenScientist plot 1
  
• OpenScientist tam10 plddt