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this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.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.
The gene mtl3 corresponds to the systematic open reading frame SPBC215.13 in Schizosaccharomyces pombe (strain 972 / ATCC 24843), encoding a protein annotated in UniProt (accession O94317) as an "Uncharacterized serine-rich protein C215.13" flagged as a precursor. Extensive literature searching revealed that the gene symbol "mtl3" does not appear directly in any of the retrieved primary research papers. The naming convention "mtl" in S. pombe follows the pattern established by the well-characterized gene mtl2 (Mid two-like 2), which encodes a cell wall stress sensor protein structurally related to Saccharomyces cerevisiae Mid2 (cruz2013thefissionyeast pages 1-2). The "mtl3" designation thus likely denotes "Mid two-like 3," implying membership in the same family of serine/threonine-rich cell surface proteins, although this relationship has not been experimentally validated for SPBC215.13.
Important caveat: This protein is largely uncharacterized in the published literature. No primary study was identified that directly investigates the biochemical function, localization, or phenotypic consequences of mtl3/SPBC215.13 deletion or mutation. The information below is therefore predominantly inference-based, drawn from computational predictions, genome-wide surveys, and analogy with better-characterized family members.
SPBC215.13 was identified as a putative GPI (glycosylphosphatidylinositol)-anchored protein in a genome-wide computational survey of fungal GPI proteins by de Groot et al. (2003). In that study, the S. pombe genome was screened using a C-terminal GPI-signal algorithm, and SPBC215.13 was among 33 GPI protein candidates identified from 4,950 ORFs (groot2003genome‐wideidentificationof pages 10-10, groot2003genome‐wideidentificationof pages 10-12). The protein was reported as approximately 226 amino acids in length with a serine/threonine (S/T) content of 22% (groot2003genome‐wideidentificationof pages 10-10). The unannotated ORFs identified in that study had an average S/T content of 41%, and the authors noted that high S/T content strengthened the likelihood that these were indeed GPI proteins (groot2003genome‐wideidentificationof pages 10-12).
The UniProt "precursor" flag indicates the presence of an N-terminal signal peptide directing the protein into the secretory pathway, consistent with its predicted cell-surface localization. GPI-anchored proteins in fungi typically possess both an N-terminal signal peptide and a C-terminal GPI-anchor addition signal that is cleaved and replaced with a GPI moiety in the endoplasmic reticulum.
The following table summarizes key features and contextual information for mtl3/SPBC215.13:
| Feature | Description/Details |
|---|---|
| Target identity | mtl3 / SPBC215.13 / UniProt O94317 in Schizosaccharomyces pombe strain 972. UniProt describes the product as an uncharacterized serine-rich precursor protein. Direct primary literature using the name mtl3 was not found in the retrieved corpus, so identity must be anchored to the systematic ID SPBC215.13 and UniProt accession O94317. |
| Evidence status | Literature for this specific protein is very limited. No direct biochemical, genetic, or localization study for SPBC215.13/mtl3 was retrieved. Most conclusions are therefore inference-based, drawn from prediction studies and comparison with related fungal cell-surface proteins (groot2003genome‐wideidentificationof pages 10-10, groot2003genome‐wideidentificationof pages 10-12). |
| Predicted protein class | A genome-wide survey of fungal GPI proteins identified SPBC215.13 among S. pombe putative GPI-anchored proteins, supporting classification as a likely cell-surface/cell-wall-associated glycoprotein rather than a soluble intracellular factor (groot2003genome‐wideidentificationof pages 10-10, groot2003genome‐wideidentificationof pages 10-12). |
| Size and composition | In the de Groot et al. table, SPBC215.13 is listed as 226 aa with 22% serine/threonine content, consistent with a serine-rich extracellular protein subject to extensive glycosylation, a common feature of fungal surface proteins (groot2003genome‐wideidentificationof pages 10-10). |
| Precursor/signal features | UniProt flags the protein as a precursor, consistent with entry into the secretory pathway. In fungal GPI proteins, this generally implies an N-terminal signal peptide plus a C-terminal GPI-anchor addition signal, although these exact features were not experimentally validated here for SPBC215.13 (groot2003genome‐wideidentificationof pages 10-10, groot2003genome‐wideidentificationof pages 10-12). |
| Predicted localization | Best current inference: cell surface, likely plasma membrane outer leaflet and/or covalently associated cell wall space after GPI anchoring/remodeling. This inference follows from the GPI-protein prediction and general fungal GPI biology (groot2003genome‐wideidentificationof pages 10-10, groot2003genome‐wideidentificationof pages 10-12, yoshimi2022cellwallintegrity pages 7-8). |
| Likely molecular role | No catalytic activity is known. The most plausible current interpretation is that SPBC215.13 is a structural or sensor-like cell-envelope protein, potentially contributing to cell wall organization, stress sensing, or wall–membrane coupling rather than acting as an enzyme with defined substrate specificity (cansado2021thefissionyeast pages 2-3, yoshimi2022cellwallintegrity pages 7-8). |
| Relationship to the name “mtl3” | The symbol mtl3 appears consistent with a Mid2-like naming convention, but this specific protein was not directly discussed in the retrieved papers. Thus, the name suggests possible membership in a broader family of cell-surface proteins related by architecture/function, but this remains unproven from current evidence. |
| Comparison to S. pombe Mtl2 | Mtl2 is a characterized cell wall stress sensor in S. pombe that localizes to the cell periphery and promotes survival under cell wall stress by activating Rho1 signaling (cruz2013thefissionyeast pages 1-2). SPBC215.13/mtl3 has no comparable direct evidence yet; similarity is currently only conceptual/name-based, not experimentally demonstrated. |
| Comparison to S. pombe Wsc1 | Wsc1 is another characterized S. pombe cell wall sensor that acts in a distinct Rho1-dependent network and localizes to growth zones/tips; it is not the same protein as mtl3/SPBC215.13 (cruz2013thefissionyeast pages 1-2, cansado2021thefissionyeast pages 2-3). |
| Comparison to S. cerevisiae Mid2/Mtl1 | In budding yeast, Mid2/Mtl1 proteins are cell wall integrity sensors with single-pass membrane anchoring, small cytosolic tails, and serine/threonine-rich, highly O-mannosylated extracellular domains that function as mechanosensors (levin2005cellwallintegrity pages 8-9, levin2005cellwallintegrity pages 9-10, cruz2013thefissionyeast pages 1-2). SPBC215.13 shares the serine-rich surface-protein logic, but unlike those classical sensors it is currently only predicted to be GPI-anchored, not experimentally shown to be a transmembrane signaling receptor. |
| Structural features of related sensors | Related fungal wall sensors typically contain STR (Ser/Thr-rich) regions that become heavily O-mannosylated, stiffening the ectodomain and enabling mechanosensory behavior at the wall–membrane interface (cansado2021thefissionyeast pages 2-3, levin2005cellwallintegrity pages 9-10, yoshimi2022cellwallintegrity pages 2-4, cruz2013thefissionyeast pages 1-2). This provides a plausible framework for interpreting a serine-rich protein such as mtl3/SPBC215.13. |
| Pathway involvement | No direct pathway assignment is currently supported for SPBC215.13. By analogy only, it could participate in cell wall integrity/homeostasis or extracellular stress-response processes, but there is no direct evidence connecting it to Rho1, Pmk1/CIP, or other defined signaling modules. |
| Biochemical activity / substrate specificity | Unknown. No enzymatic function, transported substrate, or binding partner has been experimentally established for SPBC215.13 in the retrieved literature. |
| Practical interpretation | The safest current annotation is: uncharacterized serine-rich predicted GPI-anchored cell-surface protein of S. pombe, probably associated with the cell wall/plasma membrane interface. Any stronger claim—such as calling it a bona fide mechanosensor or assigning a defined signaling role—would presently be speculative. |
Table: This table summarizes what can currently be said about the S. pombe gene mtl3/SPBC215.13 from the available literature and database-linked evidence. It distinguishes direct evidence from inference and clarifies how mtl3 relates to the better-characterized cell wall sensor proteins Mtl2, Wsc1, and budding-yeast Mid2/Mtl1.
No direct experimental localization data exists for mtl3/SPBC215.13. However, several lines of evidence support a cell surface localization:
The most parsimonious prediction is that mtl3/SPBC215.13 localizes to the plasma membrane and/or cell wall interface, with its serine-rich domain facing the extracellular/periplasmic space.
No catalytic activity, transported substrate, or direct binding partner has been experimentally established for mtl3/SPBC215.13. The protein lacks recognized enzymatic domains based on its UniProt annotation.
The naming convention and structural features of mtl3 suggest it may belong to the broader family of cell wall sensor-like proteins. In S. pombe, two such sensors have been functionally characterized:
Mtl2 (Mid two-like 2): A cell wall stress sensor that localizes to the cell periphery and is essential for survival under various cell wall stresses. Mtl2 activates the Rho1 GTPase and signals through Pck1 kinase. Deletion of mtl2 causes sensitivity to caspofungin, caffeine, vanadate, NaCl, H₂O₂, and SDS, and is associated with decreased β-1,3-glucan content (cruz2013thefissionyeast pages 1-2, yoshimi2022cellwallintegrity pages 4-5, cruz2013thefissionyeast pages 11-13).
Wsc1: A WSC-type sensor concentrated at cell tips that interacts with the Rho-GEF Rgf2 and activates glucan synthase through Rho1. Wsc1 and Mtl2 have complementary essential functions—simultaneous deletion of both is lethal, rescuable by overexpression of Rho1 or its GEFs (cruz2013thefissionyeast pages 1-2, cansado2021thefissionyeast pages 2-3).
These sensors share common structural features: small C-terminal cytoplasmic domains, a single transmembrane domain (or GPI anchor), and a periplasmic domain rich in serine/threonine residues that is extensively O-mannosylated (cansado2021thefissionyeast pages 2-3, levin2005cellwallintegrity pages 8-9, levin2005cellwallintegrity pages 9-10, cruz2013thefissionyeast pages 1-2). The O-mannosylation extends and stiffens the polypeptide, and these proteins have been proposed to function as mechanosensors whose ectodomains act as rigid probes of the extracellular matrix (levin2005cellwallintegrity pages 9-10, yoshimi2022cellwallintegrity pages 2-4).
In S. cerevisiae, the analogous family includes Wsc1-3, Mid2, and Mtl1, all of which are plasma membrane sensors for cell wall integrity that signal through Rom2 (a Rho1 GEF) to activate the cell wall integrity (CWI) MAPK pathway (levin2005cellwallintegrity pages 8-9, levin2005cellwallintegrity pages 9-10).
Given its predicted GPI-anchored, serine-rich surface protein nature, mtl3/SPBC215.13 likely participates in cell wall organization or homeostasis at the cell surface. However, whether it functions as a bona fide stress sensor (like Mtl2), a structural cell wall component, or has another role remains entirely speculative without experimental data.
It is important to distinguish mtl3/SPBC215.13 from the unrelated S. pombe protein Mtl1 (Mtr4-like 1), which is an ATP-dependent RNA helicase and a core component of the MTREC (Mtl1-Red1 core) complex. The MTREC complex is an 11-subunit nuclear RNA surveillance complex that targets cryptic unstable transcripts (CUTs), meiotic mRNAs, and unspliced pre-mRNAs for degradation by the nuclear exosome (zhou2015thefissionyeast pages 2-3, zhou2015thefissionyeast pages 8-8, dobrev2021thezincfingerprotein pages 1-2, zhou2015thefissionyeast pages 1-2). Mtl1 is an Mtr4 paralogue with 52% identity and 73% similarity to Mtr4 (dobrev2021thezincfingerprotein pages 1-2). Despite the superficial similarity in naming ("Mtl"), the MTREC helicase Mtl1 and the cell wall-associated protein mtl3/SPBC215.13 are functionally and structurally unrelated.
The gene mtl3 (SPBC215.13, UniProt O94317) in S. pombe encodes an uncharacterized serine-rich protein that is computationally predicted to be GPI-anchored and localized at the cell surface/cell wall interface (groot2003genome‐wideidentificationof pages 10-10, groot2003genome‐wideidentificationof pages 10-12). Its naming suggests it belongs to the Mid2-like family of cell wall-associated proteins, alongside the well-characterized sensor Mtl2 (cruz2013thefissionyeast pages 1-2, cansado2021thefissionyeast pages 2-3). However, no direct experimental evidence exists for its biochemical function, subcellular localization, protein interactions, or deletion phenotype. The protein has no known enzymatic activity, and no signaling pathway has been definitively linked to it.
The safest current annotation is: an uncharacterized serine-rich predicted GPI-anchored cell-surface protein, likely associated with the cell wall/plasma membrane interface, with possible involvement in cell wall organization or integrity based solely on structural analogy to related proteins. Any stronger functional claim would be speculative pending direct experimental characterization.
References
(cruz2013thefissionyeast pages 1-2): Sandra Cruz, Sofía Muñoz, Elvira Manjón, Patricia García, and Yolanda Sanchez. The fission yeast cell wall stress sensor-like proteins mtl2 and wsc1 act by turning on the gtpase rho1p but act independently of the cell wall integrity pathway. MicrobiologyOpen, 2:778-794, Jul 2013. URL: https://doi.org/10.1002/mbo3.113, doi:10.1002/mbo3.113. This article has 55 citations and is from a peer-reviewed journal.
(groot2003genome‐wideidentificationof pages 10-10): Piet W. J. de Groot, Klaas J. Hellingwerf, and Frans M. Klis. Genome‐wide identification of fungal gpi proteins. Yeast, 20:781-796, Jul 2003. URL: https://doi.org/10.1002/yea.1007, doi:10.1002/yea.1007. This article has 388 citations and is from a peer-reviewed journal.
(groot2003genome‐wideidentificationof pages 10-12): Piet W. J. de Groot, Klaas J. Hellingwerf, and Frans M. Klis. Genome‐wide identification of fungal gpi proteins. Yeast, 20:781-796, Jul 2003. URL: https://doi.org/10.1002/yea.1007, doi:10.1002/yea.1007. This article has 388 citations and is from a peer-reviewed journal.
(yoshimi2022cellwallintegrity pages 7-8): Akira Yoshimi, Ken Miyazawa, Moriyuki Kawauchi, and Keietsu Abe. Cell wall integrity and its industrial applications in filamentous fungi. Journal of Fungi, 8:435, Apr 2022. URL: https://doi.org/10.3390/jof8050435, doi:10.3390/jof8050435. This article has 50 citations.
(cansado2021thefissionyeast pages 2-3): José Cansado, Teresa Soto, Alejandro Franco, Jero Vicente-Soler, and Marisa Madrid. The fission yeast cell integrity pathway: a functional hub for cell survival upon stress and beyond. Journal of Fungi, 8:32, Dec 2021. URL: https://doi.org/10.3390/jof8010032, doi:10.3390/jof8010032. This article has 42 citations.
(levin2005cellwallintegrity pages 8-9): David E. Levin. Cell wall integrity signaling in saccharomyces cerevisiae. Microbiology and Molecular Biology Reviews, 69:262-291, Jun 2005. URL: https://doi.org/10.1128/mmbr.69.2.262-291.2005, doi:10.1128/mmbr.69.2.262-291.2005. This article has 1478 citations and is from a domain leading peer-reviewed journal.
(levin2005cellwallintegrity pages 9-10): David E. Levin. Cell wall integrity signaling in saccharomyces cerevisiae. Microbiology and Molecular Biology Reviews, 69:262-291, Jun 2005. URL: https://doi.org/10.1128/mmbr.69.2.262-291.2005, doi:10.1128/mmbr.69.2.262-291.2005. This article has 1478 citations and is from a domain leading peer-reviewed journal.
(yoshimi2022cellwallintegrity pages 2-4): Akira Yoshimi, Ken Miyazawa, Moriyuki Kawauchi, and Keietsu Abe. Cell wall integrity and its industrial applications in filamentous fungi. Journal of Fungi, 8:435, Apr 2022. URL: https://doi.org/10.3390/jof8050435, doi:10.3390/jof8050435. This article has 50 citations.
(yoshimi2022cellwallintegrity pages 4-5): Akira Yoshimi, Ken Miyazawa, Moriyuki Kawauchi, and Keietsu Abe. Cell wall integrity and its industrial applications in filamentous fungi. Journal of Fungi, 8:435, Apr 2022. URL: https://doi.org/10.3390/jof8050435, doi:10.3390/jof8050435. This article has 50 citations.
(cruz2013thefissionyeast pages 11-13): Sandra Cruz, Sofía Muñoz, Elvira Manjón, Patricia García, and Yolanda Sanchez. The fission yeast cell wall stress sensor-like proteins mtl2 and wsc1 act by turning on the gtpase rho1p but act independently of the cell wall integrity pathway. MicrobiologyOpen, 2:778-794, Jul 2013. URL: https://doi.org/10.1002/mbo3.113, doi:10.1002/mbo3.113. This article has 55 citations and is from a peer-reviewed journal.
(zhou2015thefissionyeast pages 2-3): Yang Zhou, Jianguo Zhu, Géza Schermann, Corina Ohle, Katja Bendrin, Rie Sugioka-Sugiyama, Tomoyasu Sugiyama, and Tamás Fischer. The fission yeast mtrec complex targets cuts and unspliced pre-mrnas to the nuclear exosome. Nature Communications, May 2015. URL: https://doi.org/10.1038/ncomms8050, doi:10.1038/ncomms8050. This article has 139 citations and is from a highest quality peer-reviewed journal.
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(dobrev2021thezincfingerprotein pages 1-2): Nikolay Dobrev, Yasar Luqman Ahmed, Anusree Sivadas, Komal Soni, Tamás Fischer, and Irmgard Sinning. The zinc-finger protein red1 orchestrates mtrec submodules and binds the mtl1 helicase arch domain. Nature Communications, Jun 2021. URL: https://doi.org/10.1038/s41467-021-23565-3, doi:10.1038/s41467-021-23565-3. This article has 30 citations and is from a highest quality peer-reviewed journal.
(zhou2015thefissionyeast pages 1-2): Yang Zhou, Jianguo Zhu, Géza Schermann, Corina Ohle, Katja Bendrin, Rie Sugioka-Sugiyama, Tomoyasu Sugiyama, and Tamás Fischer. The fission yeast mtrec complex targets cuts and unspliced pre-mrnas to the nuclear exosome. Nature Communications, May 2015. URL: https://doi.org/10.1038/ncomms8050, doi:10.1038/ncomms8050. This article has 139 citations and is from a highest quality peer-reviewed journal.
(dobrev2021thezincfingerprotein pages 3-4): Nikolay Dobrev, Yasar Luqman Ahmed, Anusree Sivadas, Komal Soni, Tamás Fischer, and Irmgard Sinning. The zinc-finger protein red1 orchestrates mtrec submodules and binds the mtl1 helicase arch domain. Nature Communications, Jun 2021. URL: https://doi.org/10.1038/s41467-021-23565-3, doi:10.1038/s41467-021-23565-3. This article has 30 citations and is from a highest quality peer-reviewed journal.