Mph1 (Mps1p-like pombe homolog; also called Mps1) is the fission-yeast member of the Mps1 family of dual-specificity protein kinases and an apical kinase of the spindle assembly checkpoint (SAC). It localizes to kinetochores, becoming enriched at unattached/tensionless kinetochores during mitosis, where it phosphorylates the conserved MELT repeats of the outer-kinetochore scaffold Spc7 (KNL1/Blinkin homolog). MELT phosphorylation creates a docking mark that recruits the Bub1-Bub3 complex and, downstream, Mad1-Mad2 and Mad3, generating the "wait-anaphase" signal that delays the metaphase-to-anaphase transition until all chromosomes are bioriented. Mph1 is the most upstream SAC protein in the kinetochore recruitment hierarchy (with Aurora B/Ark1), and tethering Mph1 to the kinetochore is sufficient to recruit Bub1 and to impose a checkpoint-dependent arrest. Mph1 kinase activity is also required for the mitotic checkpoint complex (Mad2-Mad3-Cdc20/Slp1) to bind and inhibit the anaphase-promoting complex (APC/C); Mph1 directly phosphorylates Mad2 and Mad3 to stabilize MCC-APC/C and maintain the arrest. Beyond the checkpoint, Mph1 is required for accurate chromosome biorientation and segregation, and mph1 deletion elevates chromosome loss even without spindle perturbation. Unlike S. cerevisiae Mps1, Mph1 is dispensable for spindle pole body duplication and for viability. Mph1 also acts in meiosis I, where it is required to prevent homolog non-disjunction. (Note: this Mps1-family kinase is unrelated to the budding-yeast/human MPH1 DNA helicase.)
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004712 protein serine/threonine/tyrosine kinase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Mph1 is a member of the Mps1 family of dual-specificity protein kinases, so the dual-specificity (Ser/Thr/Tyr) molecular function inferred from orthologs is correct. The directly demonstrated substrates in S. pombe are phosphorylated on Ser/Thr (Spc7 MELT threonines, Mad2/Mad3 sites), consistent with the family assignment. Reason: Phylogenetic inference matches the documented dual-specificity nature of the Mps1 kinase family and the demonstrated kinase activity of Mph1. Supporting Evidence: PMID:9601094 Mph1, a member of the Mps1-like family of dual specificity protein kinases, is required for the spindle checkpoint in S. pombe. |
| GO:0007094 mitotic spindle assembly checkpoint signaling | IBA GO_REF:0000033 | ACCEPT | Summary: The mitotic SAC is the core biological process of Mph1, supported by phylogenetic inference and by extensive direct experimental evidence in fission yeast (mph1Delta and kinase-dead alleles are checkpoint defective). Reason: Core function; the IBA inference is strongly corroborated by direct fission-yeast experiments. Supporting Evidence: PMID:22281223 The mph1-kd mutant was unable to arrest in mitosis, like mad2Ξ and mph1Ξ strains (Figure 1C). We conclude that Mph1 kinase activity is required for checkpoint arrest. |
| GO:0007059 chromosome segregation | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Mph1 contributes to accurate chromosome segregation; mph1 deletion and kinase-dead alleles elevate chromosome loss even without spindle perturbation. This high-level term is correct but general; the more specific mitotic SAC and biorientation terms capture the mechanistic core. Reason: Accurate but a broad parent term; retained as a non-core descriptor of the downstream consequence of Mph1 function. Supporting Evidence: PMID:22281223 These experiments demonstrate that Mph1 kinase has important chromosome segregation function(s), even when there are no extrinsic perturbations of spindle microtubules. |
| GO:0000776 kinetochore | IBA GO_REF:0000033 | ACCEPT | Summary: Mph1 acts at the kinetochore, where it phosphorylates Spc7/KNL1 MELT motifs. This is confirmed directly by immunolocalization in fission yeast (IDA), so the phylogenetic inference is correct and represents a core localization. Reason: Kinetochore localization is directly demonstrated and is where Mph1 carries out its apical SAC function. Supporting Evidence: PMID:22660415 MPS1/Mph1 kinase locating at the unattached kinetochores initially creates a mark, which is crucial for SAC activation and chromosome bi-orientation. |
| GO:0033316 meiotic spindle assembly checkpoint signaling | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Mph1 has a documented meiosis I role (preventing homolog non-disjunction), consistent with a meiotic checkpoint contribution inferred from orthologs. However, the fission yeast meiotic SAC is reportedly attenuated, and the experimentally demonstrated meiotic phenotype is homolog non-disjunction rather than a classical meiotic checkpoint assay. Retained as a plausible but non-core, meiosis-specific function. Reason: Meiosis-specific role inferred phylogenetically; real but peripheral to the central mitotic SAC function and not directly demonstrated as a meiotic checkpoint in the cached literature. Supporting Evidence: PMID:23370392 Mph1, a member of the Mps1 family of spindle assembly checkpoint kinases, is required to prevent meiosis I homolog non-disjunction. |
| GO:0034501 protein localization to kinetochore | IBA GO_REF:0000033 | ACCEPT | Summary: Mph1 drives recruitment of downstream SAC proteins to the kinetochore by phosphorylating Spc7 MELT motifs (recruiting Bub1-Bub3, and downstream Mad1-Mad2/Mad3). Centromere-tethered Mph1 is sufficient to recruit Bub1, directly supporting this inferred process. Reason: Mph1 is required for, and sufficient to drive, recruitment of SAC proteins to kinetochores; well supported by experiment. Supporting Evidence: PMID:22184248 localization of Mph1 at centromeres/kinetochores is sufficient to recruit Bub1 PMID:22521786 phosphorylation of the conserved MELT motifs in Spc7 by Mph1 (Mps1) recruits Bub1 and Bub3 to the kinetochore and that this is required to maintain the SAC signal. |
| GO:0004672 protein kinase activity | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: Generic protein kinase activity from InterPro domain mapping is correct (Mph1 has a bona fide protein kinase domain and demonstrated activity), but it is subsumed by the more specific protein serine/threonine kinase activity (IDA) and dual-specificity terms. Reason: Correct but redundant generic parent term; the experimentally supported, more specific kinase-activity terms should be preferred. Supporting Evidence: PMID:22281223 Mph1 is an active kinase that can phosphorylate itself and Mad2 in vitro |
| GO:0004712 protein serine/threonine/tyrosine kinase activity | IEA GO_REF:0000003 | ACCEPT | Summary: Dual-specificity (Ser/Thr/Tyr) kinase activity from EC 2.7.12.1 mapping is consistent with the Mps1 family classification and UniProt EC assignment. Direct pombe substrates are Ser/Thr, but the dual-specificity family property is well established. Reason: EC-based inference agrees with the documented dual-specificity family assignment and UniProt EC 2.7.12.1. Supporting Evidence: PMID:9601094 Mph1, a member of the Mps1-like family of dual specificity protein kinases, is required for the spindle checkpoint in S. pombe. |
| GO:0004713 protein tyrosine kinase activity | IEA GO_REF:0000116 | KEEP AS NON CORE | Summary: Protein tyrosine kinase activity is derived from the EC 2.7.12.1 / RHEA tyrosine autophosphorylation reaction mapping. Mph1 belongs to the dual-specificity Mps1 family, for which tyrosine (auto)phosphorylation is a recognized property, but no specific tyrosine substrate has been demonstrated in S. pombe in the cached literature. Reason: Supported by the dual-specificity family classification and EC/RHEA mapping; retained as non-core because direct tyrosine-substrate evidence in fission yeast is lacking. Supporting Evidence: PMID:9601094 Mph1, a member of the Mps1-like family of dual specificity protein kinases, is required for the spindle checkpoint in S. pombe. |
| GO:0005524 ATP binding | IEA GO_REF:0000002 | ACCEPT | Summary: ATP binding is correct: Mph1 has a canonical protein kinase ATP-binding pocket (glycine-rich loop residues 322-330 and invariant Lys345) and uses ATP to phosphorylate substrates in vitro. Reason: A required molecular function for this active protein kinase, supported by the conserved ATP-binding motif and demonstrated kinase activity. Supporting Evidence: PMID:22281223 Affinity-purified Mph1-SZZ kinase was incubated with Ξ³-[32P]ATP and recombinant Mad2 substrate |
| GO:0007094 mitotic spindle assembly checkpoint signaling | IEA GO_REF:0000117 | ACCEPT | Summary: Same core mitotic SAC process as the experimentally supported annotations, here generated by an ARBA machine-learning rule. Correct and redundant with the IMP/EXP/IBA annotations. Reason: Correct core function; consistent with multiple experimental annotations to the same term. Supporting Evidence: PMID:9601094 mph1 functions upstream of mad2, a previously characterized component of the spindle checkpoint. |
| GO:0098813 nuclear chromosome segregation | IEA GO_REF:0000117 | KEEP AS NON CORE | Summary: Nuclear chromosome segregation (ARBA rule) is correct but a general parent of the more specific mitotic SAC and biorientation roles. Mph1 acts in the closed mitosis of fission yeast on nuclear chromosomes, so the term is accurate but non-core. Reason: Accurate broad descriptor of the downstream consequence; the specific SAC/biorientation terms capture the mechanism. Supporting Evidence: PMID:22281223 These experiments demonstrate that Mph1 kinase has important chromosome segregation function(s), even when there are no extrinsic perturbations of spindle microtubules. |
| GO:0106310 protein serine kinase activity | IEA GO_REF:0000116 | ACCEPT | Summary: Protein serine kinase activity (RHEA mapping) is correct and directly demonstrated: Mph1 phosphorylates serine and threonine residues of its substrates (e.g., Mad2/Mad3 sites). It is a more specific component of the dual-specificity activity. Reason: Consistent with experimentally demonstrated Ser/Thr phosphorylation of Mph1 substrates. Supporting Evidence: PMID:22281223 Mph1 is an active kinase that can phosphorylate itself and Mad2 in vitro |
| GO:0000776 kinetochore | IDA PMID:22660415 MPS1/Mph1 phosphorylates the kinetochore protein KNL1/Spc7 t... | ACCEPT | Summary: Direct experimental evidence places Mph1 at the kinetochore, enriched at unattached kinetochores, where it phosphorylates Spc7. This is a core localization for Mph1. Reason: Directly demonstrated kinetochore localization at the site of Mph1 catalytic function. Supporting Evidence: PMID:22660415 MPS1/Mph1 kinase locating at the unattached kinetochores initially creates a mark, which is crucial for SAC activation and chromosome bi-orientation. |
| GO:0004674 protein serine/threonine kinase activity | IDA PMID:22660415 MPS1/Mph1 phosphorylates the kinetochore protein KNL1/Spc7 t... | ACCEPT | Summary: Mph1 directly phosphorylates Spc7/KNL1 on the threonine residues of MELT motifs, demonstrating protein serine/threonine kinase activity. This is a core molecular function. Reason: Directly demonstrated Ser/Thr kinase activity on a physiological substrate (Spc7 MELT motifs). Supporting Evidence: PMID:22660415 fission yeast Mph1 (MPS1 homologue) phosphorylates the kinetochore protein Spc7 (KNL1/Blinkin homologue) at the MELT repeat sequences. |
| GO:0007094 mitotic spindle assembly checkpoint signaling | IMP PMID:22825872 Mph1 kinetochore localization is crucial and upstream in the... | ACCEPT | Summary: Mph1 kinetochore recruitment is crucial and upstream for a stable SAC arrest; an Mph1 mutant that loses kinetochore enrichment abolishes SAC signaling, and forced kinetochore recruitment restores it. Strong support for the core mitotic SAC function. Reason: Direct mutant-phenotype evidence that Mph1 is the apical kinetochore kinase required for the mitotic SAC. Supporting Evidence: PMID:22825872 An Mph1 mutant that eliminates kinetochore enrichment abolishes SAC signaling, whereas forced recruitment of this mutant to kinetochores restores SAC signaling. |
| GO:0004674 protein serine/threonine kinase activity | EXP PMID:28497540 Meikin-associated polo-like kinase specifies Bub1 distributi... | ACCEPT | Summary: Mph1 serine/threonine kinase activity in the context of the meiotic Spc7/Bub1 recruitment pathway. This study (meikin/Moa1-Plo1-Spc7-Bub1 axis) was full-text reviewed by the PomBase curator; the cached version is abstract-only. The Ser/Thr kinase activity assertion is consistent with all other evidence for Mph1 and is accepted. Reason: Consistent with the well-established Ser/Thr kinase activity of Mph1; defer to PomBase curator who read the full text. Supporting Evidence: PMID:22660415 fission yeast Mph1 (MPS1 homologue) phosphorylates the kinetochore protein Spc7 (KNL1/Blinkin homologue) at the MELT repeat sequences. |
| GO:0007094 mitotic spindle assembly checkpoint signaling | EXP PMID:22660415 MPS1/Mph1 phosphorylates the kinetochore protein KNL1/Spc7 t... | ACCEPT | Summary: Phosphorylation of Spc7 MELT motifs by Mph1 is required for kinetochore-based SAC activation (Mad1-Mad2-Mad3 localization). Core mitotic SAC function with direct experimental support. Reason: Direct experimental demonstration of Mph1's role in mitotic SAC activation via Spc7 phosphorylation. Supporting Evidence: PMID:22660415 This phosphorylation promotes the in vitro binding to the Bub1-Bub3 complex, which is required for kinetochore-based SAC activation (Mad1-Mad2-Mad3 localization) and chromosome alignment. |
| GO:1990813 meiotic centromeric cohesion protection in anaphase I | IMP PMID:28497540 Meikin-associated polo-like kinase specifies Bub1 distributi... | KEEP AS NON CORE | Summary: This annotation links Mph1 to protection of centromeric cohesion in meiosis I, via the meikin(Moa1)-Plo1-Spc7-Bub1-Sgo1 pathway in which Spc7 phosphorylation accumulates Bub1 to promote Sgo1-dependent cohesion protection. The cached file is abstract-only (foregrounds Plo1/Moa1), so the specific Mph1 contribution cannot be fully verified here; the PomBase curator made this IMP from the full text. Retained as a meiosis-specific, non-core function. Reason: Meiosis-specific role made by an expert curator from full text not in our cache; consistent with Mph1's Spc7/Bub1 axis. Per curation guidance, defer rather than remove. Supporting Evidence: PMID:28497540 recruits Plo1 (polo-like kinase) to the kinetochores and phosphorylates Spc7 (KNL1) to accumulate Bub1 PMID:23370392 We thus conclude that Mph1 is required for efficient homolog disjunction during meiosis I. |
| GO:0004674 protein serine/threonine kinase activity | EXP PMID:27618268 Bub3-Bub1 Binding to Spc7/KNL1 Toggles the Spindle Checkpoin... | ACCEPT | Summary: Mph1 Ser/Thr kinase activity in the context of phosphorylating Spc7 MELT motifs to toggle the SAC switch. Consistent with all other kinase-activity evidence for Mph1. Reason: Consistent with directly demonstrated Ser/Thr kinase activity on Spc7 MELT motifs. Supporting Evidence: PMID:27618268 Mph1 (Mps1) phosphorylates multiple conserved MELT motifs in the Spc7 (Spc105/KNL1) protein to recruit Bub1, Bub3, and Mad3 (BubR1) to kinetochores |
| GO:0007094 mitotic spindle assembly checkpoint signaling | IMP PMID:9601094 Mph1, a member of the Mps1-like family of dual specificity p... | ACCEPT | Summary: The founding study identifying mph1 as a spindle checkpoint gene required for checkpoint activation in response to spindle defects, acting upstream of mad2. Core mitotic SAC function. Reason: Original genetic identification of Mph1 as a SAC gene upstream of mad2; core function. Supporting Evidence: PMID:9601094 we report the isolation of a new spindle checkpoint gene, mph1 (Mps1p-like pombe homolog), in the fission yeast Schizosaccharomyces pombe, that is required for checkpoint activation in response to spindle defects. mph1 functions upstream of mad2 |
| GO:0000776 kinetochore | IDA PMID:22184248 Centromere-tethered Mps1 pombe homolog (Mph1) kinase is a su... | ACCEPT | Summary: A second direct demonstration of Mph1 kinetochore/centromere localization; centromere-tethered Mph1 is sufficient to recruit Bub1, confirming both the localization and its functional output. Reason: Independent direct evidence for kinetochore localization, the core site of Mph1 action. Supporting Evidence: PMID:22184248 localization of Mph1 at centromeres/kinetochores is sufficient to recruit Bub1 |
| GO:0004674 protein serine/threonine kinase activity | IDA PMID:22281223 Kinase activity of fission yeast Mph1 is required for Mad2 a... | ACCEPT | Summary: Affinity-purified Mph1 phosphorylates itself and Mad2 in vitro using ATP, and the D459A kinase-dead allele abolishes this activity, directly demonstrating Ser/Thr kinase activity. Reason: Direct in vitro demonstration of catalytic kinase activity, abolished by an active-site mutation. Supporting Evidence: PMID:22281223 Mph1 is an active kinase that can phosphorylate itself and Mad2 in vitro; second, the D459A substitution has βkilledβ Mph1 kinase activity |
| GO:0007094 mitotic spindle assembly checkpoint signaling | IMP PMID:22281223 Kinase activity of fission yeast Mph1 is required for Mad2 a... | ACCEPT | Summary: The mph1 kinase-dead allele is checkpoint defective and fails to assemble/maintain MCC-APC/C complexes, showing Mph1 kinase activity is required for the mitotic SAC. Core function. Reason: Direct mutant evidence that Mph1 kinase activity is required for mitotic checkpoint arrest and MCC-APC/C formation. Supporting Evidence: PMID:22281223 Both mph1 mutants failed to assemble significant levels of MCC-APC/C, and both failed to checkpoint arrest, highlighting the importance of Mph1 kinase activity in the spindle checkpoint. |
| GO:0004674 protein serine/threonine kinase activity | EXP PMID:26882497 Mps1Mph1 Kinase Phosphorylates Mad3 to Inhibit Cdc20Slp1-APC... | ACCEPT | Summary: Mph1 directly phosphorylates Mad3 (sixteen in vitro sites; the kinase-dead control fails), demonstrating Ser/Thr kinase activity on a checkpoint substrate. Core molecular function. Reason: Direct in vitro kinase assay with Mad3 substrate confirms Mph1 Ser/Thr kinase activity. Supporting Evidence: PMID:26882497 we identify Mad3 as a substrate of fission yeast Mps1(Mph1) kinase. |
| GO:0007094 mitotic spindle assembly checkpoint signaling | IMP PMID:26882497 Mps1Mph1 Kinase Phosphorylates Mad3 to Inhibit Cdc20Slp1-APC... | ACCEPT | Summary: Mph1-dependent phosphorylation of Mad3 (and Mad2) stabilizes MCC-APC/C binding and is required to maintain spindle checkpoint arrests, supporting Mph1's core mitotic SAC role through direct substrate modification. Reason: Demonstrates Mph1's mitotic SAC function via phosphorylation of the MCC component Mad3. Supporting Evidence: PMID:26882497 Mps1(Mph1) kinase-dependent modifications of Mad3 and Mad2 act in a concerted manner to maintain spindle checkpoint arrests. |
| GO:0007094 mitotic spindle assembly checkpoint signaling | IMP PMID:22521786 Phosphodependent recruitment of Bub1 and Bub3 to Spc7/KNL1 b... | ACCEPT | Summary: Phosphorylation of Spc7 MELT motifs by Mph1 recruits Bub1-Bub3 to kinetochores and is required to maintain the SAC signal; mph1Delta and D459A fail to localize Bub1. Core mitotic SAC function. Reason: Direct demonstration that Mph1 kinase activity maintains the SAC via Spc7 MELT phosphorylation and Bub1-Bub3 recruitment. Supporting Evidence: PMID:22521786 Bub1 fails to form discrete foci during mitosis in either Ξmph1 or mph1(D459A) mutants (which are defective for kinase activity [23]), indicating that catalytic activity of Mph1 is required to promote kinetochore association of Bub1 |
| GO:0004674 protein serine/threonine kinase activity | IDA PMID:22521786 Phosphodependent recruitment of Bub1 and Bub3 to Spc7/KNL1 b... | ACCEPT | Summary: Mph1 directly phosphorylates the Spc7 N-terminal half in vitro on MELT-motif threonines, demonstrating Ser/Thr kinase activity on a physiological kinetochore substrate. Reason: Direct in vitro kinase assay on Spc7 MELT motifs confirms Mph1 Ser/Thr kinase activity. Supporting Evidence: PMID:22521786 We find that Mph1 phosphorylates Spc7 in vitro on two threonine residues (T453 and T507) which are part of a repetitive motif of unknown function, termed the MELT motif |
| GO:0007127 meiosis I | IMP PMID:23370392 A knockout screen for protein kinases required for the prope... | KEEP AS NON CORE | Summary: mph1 deletion causes meiosis I homolog non-disjunction and lagging chromosomes, indicating a requirement for Mph1 in proper homolog disjunction during meiosis I (likely via preventing precocious anaphase I entry). A genuine but meiosis-specific, non-core function. Reason: Directly demonstrated meiosis I role, but peripheral relative to Mph1's central mitotic SAC function. Supporting Evidence: PMID:23370392 We thus conclude that Mph1 is required for efficient homolog disjunction during meiosis I. |
| GO:0005634 nucleus | HDA PMID:16823372 ORFeome cloning and global analysis of protein localization ... | ACCEPT | Summary: Genome-wide YFP localization assigned Mph1 a nuclear signal. Fission yeast undergoes closed mitosis and Mph1 acts on intranuclear kinetochores and on the nucleoplasmic MCC/APC-C, so a nuclear pool is consistent with its biology. Reason: High-throughput localization consistent with Mph1 acting on nuclear kinetochores and nucleoplasmic checkpoint complexes in closed mitosis. Supporting Evidence: PMID:16823372 we determined the localization of 4,431 proteins, corresponding to approximately 90% of the fission yeast proteome, by tagging each ORF with the yellow fluorescent protein. |
| GO:0005829 cytosol | HDA PMID:16823372 ORFeome cloning and global analysis of protein localization ... | KEEP AS NON CORE | Summary: The same genome-wide study reported a cytosolic signal for Mph1. A soluble/cytoplasmic pool is plausible (only a fraction of Mph1 is kinetochore-bound at any time), but the functionally important pools are the kinetochore and nucleoplasm. Retained as non-core. Reason: High-throughput cytosolic signal; plausible soluble pool but not the principal functional site. Supporting Evidence: PMID:16823372 we determined the localization of 4,431 proteins, corresponding to approximately 90% of the fission yeast proteome, by tagging each ORF with the yellow fluorescent protein. |
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Download this section (compressed HTML)Q: Does Mph1 phosphorylate any physiological tyrosine substrate in fission yeast, or is its tyrosine activity restricted to autophosphorylation, as the dual-specificity EC assignment would predict?
Q: What is the relative contribution of kinetochore-localized Mph1 (Spc7 MELT phosphorylation) versus nucleoplasmic Mph1 (direct Mad2/Mad3 phosphorylation) to establishing versus maintaining the checkpoint arrest?
Q: Is the meiosis I homolog non-disjunction phenotype of mph1Delta solely a consequence of a weakened SAC and precocious anaphase I, or does Mph1 contribute directly to the meikin/Bub1/Sgo1 cohesion-protection pathway?
Experiment: Use analog-sensitive mph1 (or chemical Mps1 inhibition) combined with quantitative phosphoproteomics across synchronized mitosis to define the in vivo Mph1 substrate repertoire and distinguish kinetochore from nucleoplasmic targets.
Experiment: Reconstitute Mph1 with recombinant Spc7, Bub1-Bub3 and Mad1-Mad2 in vitro to test whether MELT phosphorylation is sufficient to assemble a functional checkpoint signaling module and to map the order of recruitment events.
Experiment: Separate Mph1 mitotic and meiotic functions using meiosis-specific depletion or separation-of-function alleles, and score homolog disjunction, Bub1/Sgo1 centromeric accumulation, and Rec8 cohesion protection in meiosis I.
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