Spo2 is a small (133 aa, about 15 kDa) meiosis-induced protein of fission yeast that is required for sporulation but not for the meiotic nuclear divisions. Its expression is driven by the forkhead transcription factor Mei4. During meiosis II Spo2 is recruited to the cytoplasmic face of the spindle pole body (SPB) by the constitutive SPB component Spo15, and it in turn recruits Spo13; Spo2 binds both proteins, which do not bind each other directly. This ordered Spo15-Spo2-Spo13 assembly converts the SPB outer plaque into the meiotic outer plaque that initiates forespore membrane formation. The Spo2 sequence is identical to the C-terminal 133 residues of the overlapping vps1302 gene model but contains none of the VPS13 lipid-transfer domains, and Spo2 has no recognised homologues outside the fission-yeast lineage.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005515 protein binding | IPI PMID:18367542 Meiotic spindle pole bodies acquire the ability to assemble ... | MODIFY | Summary: Spo2 physically associates with Spo15 (SPAC1F3.06c), the constitutive SPB component that recruits it to the meiotic SPB. Reason: Generic protein binding is uninformative. Spo2 binds both Spo15 and Spo13, which do not interact directly, and Spo13 needs Spo2 to reach the SPB. Together these data support a bridging adaptor activity that brings the two SPB components together, captured by protein-macromolecule adaptor activity (an is_a child of molecular adaptor activity). The Spo15 interaction is one half of that bridge. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:18367542 Spo2 physically associated with both Spo15 and Spo13, but Spo13 and Spo15 did not interact directly. PMID:18367542 Localization of Spo13 to the SPB was dependent on Spo15 and Spo2; that of Spo2 depended only on Spo15 |
| GO:0005515 protein binding | IPI PMID:18367542 Meiotic spindle pole bodies acquire the ability to assemble ... | MODIFY | Summary: Spo2 physically associates with Spo13 (SPCC1183.12), the coiled-coil protein that it recruits to the outer surface of the meiotic SPB. Reason: As for the Spo15 row, the informative claim is the bridging adaptor activity linking Spo15 to Spo13, not generic binding; Spo13 depends on Spo2 for SPB localization and Spo13 does not bind Spo15 directly. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:18367542 Spo2 physically associated with both Spo15 and Spo13, but Spo13 and Spo15 did not interact directly. PMID:18367542 Localization of Spo13 to the SPB was dependent on Spo15 and Spo2; that of Spo2 depended only on Spo15 |
| GO:0005816 spindle pole body | IEA GO_REF:0000044 | MODIFY | Summary: Spo2 is at the spindle pole body, but only the meiotic SPB. Reason: Correct but general. Spo2 is meiosis-specific (Mei4-induced, absent from vegetative cells) and was observed only at the meiotic SPB; meiotic spindle pole body (GO:0035974, is_a spindle pole body) is the precise term and the gene already carries it by IDA. Proposed replacements: meiotic spindle pole body Supporting Evidence: PMID:18367542 Spo13 and Spo2 localized on the cytoplasmic side of the SPB in close contact with the nascent FSM. PMID:18367542 Both Spo13 and Spo2 specifically associated with the meiotic SPB. |
| GO:0030437 ascospore formation | IMP PMID:18367542 Meiotic spindle pole bodies acquire the ability to assemble ... | MODIFY | Summary: spo2 deletion abolishes sporulation without blocking meiotic nuclear division. Reason: True, but the same study pins Spo2's contribution to a specific step of ascospore formation, SPB modification preceding forespore membrane initiation. GO:0031322 ascospore-type prospore-specific spindle pole body remodeling is a descendant of ascospore formation (via ascospore-type prospore assembly) and the gene already carries it by IMP, so the specific term is the better statement of what Spo2 does. Proposed replacements: ascospore-type prospore-specific spindle pole body remodeling Supporting Evidence: PMID:18367542 The respective deletion mutants are viable, but defective in SPB modification and in the onset of FSM formation. PMID:18367542 which are not required for progression of meiotic nuclear divisions, but are essential for sporulation. |
| GO:0031322 ascospore-type prospore-specific spindle pole body remodeling | IMP PMID:18367542 Meiotic spindle pole bodies acquire the ability to assemble ... | ACCEPT | Summary: Spo2 is required for SPB modification (meiotic outer plaque formation) during meiosis II. Reason: The term definition explicitly includes recruitment of sporulation-specific proteins to the outer plaque. Spo2 is itself one of those recruited proteins and performs part of the work by recruiting Spo13; the deletion mutant is defective in SPB modification. This is participation, not merely necessity. Supporting Evidence: PMID:18367542 The respective deletion mutants are viable, but defective in SPB modification and in the onset of FSM formation. PMID:18367542 Localization of Spo13 to the SPB was dependent on Spo15 and Spo2; that of Spo2 depended only on Spo15 PMID:18367542 Spo2 physically associated with both Spo15 and Spo13, but Spo13 and Spo15 did not interact directly. |
| GO:0035974 meiotic spindle pole body | IDA PMID:18367542 Meiotic spindle pole bodies acquire the ability to assemble ... | ACCEPT | Summary: Spo2 localizes to the cytoplasmic face of the meiotic spindle pole body. Reason: Direct localization of functional tagged Spo2 to the meiotic SPB, where it acts to recruit Spo13. Proximity to the nascent forespore membrane does not establish membrane residence, so no membrane location is proposed. Supporting Evidence: PMID:18367542 Spo13 and Spo2 localized on the cytoplasmic side of the SPB in close contact with the nascent FSM. PMID:18367542 Both Spo13 and Spo2 specifically associated with the meiotic SPB. |
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Download this section (compressed HTML)Q: Is spo2 expressed as an independent meiotic transcript initiating at the codon equivalent to Vps1302 Met2999, and does the vps1302 gene model correctly extend through the spo2 coding region?
Q: Which regions of the 133-residue Spo2 mediate binding to Spo15 and to Spo13, and are they separable?
Experiment: Map the 5' ends of meiotic spo2 transcripts (e.g. TSS-seq or 5' RACE across a meiotic time course) and test whether a spo2 start-codon mutation that leaves the vps1302 frame intact abolishes sporulation, to separate spo2 function from that of the overlapping vps1302 locus.
Experiment: Use truncation and point mutants of Spo2 in two-hybrid and co-immunoprecipitation assays to define Spo15- and Spo13-binding regions, and test whether a mutant that binds Spo15 but not Spo13 localizes to the SPB yet fails to recruit Spo13 and to initiate forespore membrane formation.
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