Mih1 is the budding-yeast member of the Cdc25 family of M-phase inducer phosphatases: a rhodanese-fold, dual-specificity protein phosphatase (catalytic Cys320 in the HCX5R active-site loop) whose physiological substrate is the cyclin-dependent kinase Cdc28 (Cdk1) phosphorylated on the inhibitory residue Tyr19. By removing the phosphate placed on Tyr19 by the Wee1-family kinase Swe1, Mih1 activates Cdc28-Clb (mitotic cyclin) complexes and promotes the G2/M transition, and it is the structural and functional counterpart of fission-yeast cdc25. Unlike cdc25, Mih1 is not essential and is not rate-limiting for mitotic entry in an unperturbed cycle: mih1 null cells show only a Swe1-dependent G2 delay, because the phosphatase Ptp1 and a PP2A-Rts1-dependent activity provide redundant routes to Cdc28-Tyr19 dephosphorylation. The Swe1-Mih1 balance becomes decisive when the morphogenesis checkpoint is engaged (cells that fail to bud or polarize, septin mutants, hsl1 or hsl7 mutants): the timing of nuclear division is then exquisitely sensitive to MIH1 and SWE1 gene dosage, and loss of MIH1 converts a transient G2 delay into a permanent arrest with elongated buds, while MIH1 overexpression suppresses the lethality of SWE1 overexpression. Mih1 is a nucleocytoplasmic protein that is predominantly cytoplasmic through most of the cell cycle and accumulates in the nucleus in late mitosis through an N-terminal basic import signal; because Cdc28-Clb2 itself shuttles, Mih1 can act on it from either compartment, but the nuclear pool is the more effective one. Mih1 abundance is roughly constant across the cycle and its output is set post-translationally: it is hyperphosphorylated through interphase by casein kinase 1 (Yck1/Yck2) and other kinases, and is dephosphorylated by PP2A-Cdc55 (whose activity toward Mih1 depends on Zds1/Zds2 and the endosulfines Igo1/Igo2) as cells approach mitosis; the Polo kinase Cdc5 also acts on Mih1. Mih1 additionally influences anaphase spindle elongation dynamics through the phosphorylation state of the microtubule-associated protein Bik1, and in meiosis it removes Cdc28-Tyr19 phosphorylation at the prophase I to meiosis I transition, where Cdc5 promotes its nuclear entry after the recombination checkpoint is satisfied. Outside the cell cycle, Mih1 dephosphorylates the Vps26 subunit of retromer, and the phosphorylation state of Vps26 tunes its affinity for retromer cargo and the recycling of a subset of endocytosed plasma membrane proteins from the endosome.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000086 G2/M transition of mitotic cell cycle | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT propagation from the Cdc25-family node PTN000089071, seeded by Drosophila string, human CDC25A/B/C and MIH1's own SGD experimental annotation. Mih1 acts at the G2/M transition by removing the Swe1-dependent inhibitory Tyr19 phosphate from Cdc28, activating Cdc28-Clb2 for mitotic entry. Core process. Reason: The node placement is sound: the G2/M role of the Cdc25 family is ancestral, and MIH1 appears among the descendant evidences because of its own IMP annotation (PMID:2649252), which is the expected marker that experimental grounding exists on the target itself. Budding-yeast genetics is fully consistent (mih1 mutants have a Swe1-dependent G2 delay; Swe1/wee1+ overexpression blocks mitosis without MIH1). Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000089071 SUPPORTS TRANSFER Current PTHR10828 PAINT places the G2/M transition IBD at this Cdc25-family node. MIH1 descends from the node and is itself one of the experimental descendants, which is expected target grounding. Supporting Evidence: PMID:2649252 The wee1+ activity is counteracted in S. cerevisiae by the gene product of MIH1, a newly identified gene capable of encoding a protein of MW 54,000, which is a structural and functional homolog of the cdc25+ mitotic inducer of fission yeast. PMID:8253069 deletion of SWE1 did not alter the cell cycle but did eliminate the G2 delay observed in mih1- mutants |
| GO:0000086 G2/M transition of mitotic cell cycle | IMP PMID:2649252 Conservation of mitotic controls in fission and budding yeas... | ACCEPT | Summary: The founding MIH1 paper: MIH1 was cloned as the budding-yeast gene that counteracts fission-yeast wee1+ kinase expressed in S. cerevisiae, and wee1+ expression in a mih1- strain prevents the initiation of mitosis. This is direct mutant-phenotype evidence that Mih1 functions at the G2/M transition as the Cdc25 counterpart of Wee1/Swe1. Core process. Reason: Classical IMP evidence read by SGD from the full text; the cached abstract alone states the key result. Later work confirmed that the mih1 G2 delay is entirely Swe1-dependent and that Mih1 is not essential because Ptp1 and PP2A-Rts1 provide redundant Cdc28-Tyr19 dephosphorylation, but that does not weaken the assignment of Mih1 to the G2/M transition. Supporting Evidence: PMID:2649252 Expression of wee1+ in a mih1- strain prevents the initiation of mitosis. PMID:22918234 The S. cerevisiae Cdc25 phosphatase homolog, Mih1, antagonizes Swe1 Cdk1-Y19 phosphorylation but is not essential for mitotic progression, unlike its counterpart in Schizosaccharomyces pombe |
| GO:0004725 protein tyrosine phosphatase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Core molecular function propagated from the Cdc25 tyrosine-phosphatase node PTN000850864 (seeded by S. pombe cdc25, human CDC25A/B, rat, fly and Arabidopsis members). Mih1 removes the Swe1-placed phosphate from Cdc28 Tyr19; purified Mih1 directly dephosphorylates Swe1-phosphorylated Cdc28-Clb2 in vitro. Reason: The catalytic activity is ancestral to the family (rhodanese fold with the conserved HCX5R motif; active-site Cys320 in Mih1) and is directly demonstrated for the budding-yeast protein against its physiological substrate. Mih1 is formally a dual-specificity phosphatase, but the only characterised physiological reaction is Tyr19 dephosphorylation, so the PTP term is the right level. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000850864 SUPPORTS TRANSFER Current PTHR10828 PAINT places protein tyrosine phosphatase activity on the Cdc25-family node that contains MIH1, and direct target biochemistry supports retention. Supporting Evidence: PMID:16688214 cells unable to activate Cdc28 by tyrosine 19 dephosphorylation (Y19) catalyzed by Mih1 (homolog of Cdc25 phosphatase) PMID:21536748 Mih1 phosphatase (Cdc25 homologue) removes this inhibitory phosphorylation to promote mitotic entry |
| GO:0004725 protein tyrosine phosphatase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Automated mapping from the MPI phosphatase InterPro family (IPR000751), EC 3.1.3.48 and RHEA:10684 (protein-tyrosine-phosphate hydrolysis). Consistent with the experimentally established Cdc28-Tyr19 phosphatase activity of Mih1. Reason: Electronic inference that coincides with the IBA and direct evidence; the family mapping is not over-general for a bona fide Cdc25 phosphatase. Supporting Evidence: PMID:21536748 Mih1 phosphatase (Cdc25 homologue) removes this inhibitory phosphorylation to promote mitotic entry |
| GO:0004725 protein tyrosine phosphatase activity | ISS GO_REF:0000024 | ACCEPT | Summary: UniProt curator transfer of protein tyrosine phosphatase activity from human CDC25A (P30303). Correct: Mih1 is the sole budding-yeast Cdc25 and dephosphorylates Cdc28-Tyr19. Reason: Sequence-similarity transfer that is redundant with, and fully corroborated by, the IBA and budding-yeast experimental evidence for Cdc28-Tyr19 dephosphorylation. Supporting Evidence: PMID:16688214 cells unable to activate Cdc28 by tyrosine 19 dephosphorylation (Y19) catalyzed by Mih1 (homolog of Cdc25 phosphatase) |
| GO:0004725 protein tyrosine phosphatase activity | ISS PMID:2649252 Conservation of mitotic controls in fission and budding yeas... | ACCEPT | Summary: SGD ISS transfer from S. pombe cdc25 (P06652), based on the original paper showing MIH1 to be a structural and functional homolog of cdc25+. The activity is now directly demonstrated for Mih1 (purified Mih1 dephosphorylates Swe1-phosphorylated Cdc28-Clb2, Kennedy et al. 2016, PMID:26715668), so the inference is sound. Reason: Correct molecular function; the ISS could be upgraded to a direct-assay code from later biochemistry, but the term and its assignment are right. Supporting Evidence: PMID:2649252 which is a structural and functional homolog of the cdc25+ mitotic inducer of fission yeast file:yeast/MIH1/MIH1-deep-research-falcon.md Purified Mih1 removed Cdc28 Tyr19 phosphorylation directly. |
| GO:0005634 nucleus | HDA PMID:14562095 Global analysis of protein localization in budding yeast. | ACCEPT | Summary: Genome-wide GFP-fusion localization (Huh et al. 2003) scoring Mih1 in the nucleus as well as the cytoplasm. Focused studies agree: Mih1 is largely cytoplasmic in interphase and accumulates in the nucleus in late mitosis (vegetative cycle) and at the prophase I to metaphase I transition (meiosis) via an N-terminal basic import signal. Reason: High-throughput evidence concordant with directed localization studies of tagged Mih1; the nucleus is where the substrate Cdc28-Clb2 is concentrated at mitotic entry. Supporting Evidence: PMID:41927924 As cells transitioned from prophase I to metaphase I, Mih1 progressively accumulated in the nucleus, coinciding with SPB separation. |
| GO:0005634 nucleus | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference that Cdc25-family phosphatases act in the nucleus, from fly, mouse, worm, human and S. pombe members. For Mih1, a cytoplasm-restricted mutant (Lys31-33 to Ala) is less effective at promoting nuclear division and an appended SV40 NLS restores function, and in meiosis Cdc5-driven nuclear entry of Mih1 accompanies Cdc28-Tyr19 dephosphorylation, so the nuclear pool is active. Reason: Consistent with direct localization and function data for Mih1 (Keaton et al. 2008, PMID:18562688; PMID:41927924). Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000850864 SUPPORTS TRANSFER The conserved Cdc25 phosphatase node carries a nucleus IBD in current PTHR10828 PAINT; focused Mih1 localization and function data show that the budding-yeast nuclear pool is active. Supporting Evidence: PMID:41927924 Cdc5 promotes Cdk1 activation by inducing Swe1 degradation and facilitating Mih1 nuclear translocation. |
| GO:0005737 cytoplasm | HDA PMID:14562095 Global analysis of protein localization in budding yeast. | ACCEPT | Summary: Genome-wide GFP-fusion localization scoring Mih1 in the cytoplasm. Directed studies show Mih1 is predominantly cytoplasmic through most of the vegetative cycle and during meiotic prophase I, with transient nuclear accumulation later. Reason: Concordant with immunofluorescence and live-cell GFP-Mih1 imaging. Supporting Evidence: PMID:41927924 during meiotic prophase I, Mih1 was predominantly cytoplasmic and largely excluded from the nucleus |
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference of a cytoplasmic site of action. For Mih1 this is supported: the cytoplasm-restricted Lys31-33Ala mutant still promotes nuclear division (less efficiently), showing Mih1 can act on shuttling Cdc28-Clb2 from the cytoplasm. Reason: Both the family-level inference and the budding-yeast data indicate a functional cytoplasmic pool; the nucleus/cytoplasm pair together describes a shuttling enzyme. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000850864 SUPPORTS TRANSFER The current cytoplasm IBD is at the Cdc25-family node and is compatible with Mih1's documented shuttling between cytoplasm and nucleus. Supporting Evidence: PMID:41927924 during meiotic prophase I, Mih1 was predominantly cytoplasmic and largely excluded from the nucleus |
| GO:0010971 positive regulation of G2/M transition of mitotic cell cycle | IBA GO_REF:0000033 | ACCEPT | Summary: Core process, propagated from node PTN000089071 (S. pombe cdc25, human CDC25A/B). The directional term captures what Mih1 does: it activates the cyclin-dependent kinase Cdc28 by Tyr19 dephosphorylation, opposing Swe1, and its overexpression forces mitotic entry (rescuing GAL-SWE1 lethality and the cdc55/zds1 zds2 G2 delay). Reason: Fits the term definition exactly (a pathway that activates the cell cycle CDK to promote the G2/M switch) and is the most specific correct process term for Mih1. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000089071 SUPPORTS TRANSFER PTN000089071 carries the positive G2/M-transition regulation IBD in current PTHR10828 PAINT, and the propagated directional process matches Mih1-mediated removal of inhibitory Cdc28-Tyr19 phosphate. Supporting Evidence: PMID:9744879 GAL1::MIH1 rescues the lethality of a GAL1::SWE1 strain grown on galactose media. PMID:21536748 the hyperelongated morphology of cdc55Ξ and zds1Ξ zds2Ξ is rescued either by deletion of SWE1 (McMillan et al., 1999a; Yang et al., 2000), by overexpression of MIH1 (McMillan et al., 1999a) |
| GO:0051231 spindle elongation | IMP PMID:30072442 Swe1 and Mih1 regulate mitotic spindle dynamics in budding y... | KEEP AS NON CORE | Summary: Raspelli et al. 2018 report that the Swe1/Cdc5-controlled phosphorylation state of Mih1 is important for mitotic spindle elongation and that Swe1 and Mih1 control phosphorylation of the microtubule-associated protein Bik1. This is a genuine mih1 mutant phenotype, but the effect is upstream (through Cdc28 activity and Bik1 phosphorylation) rather than Mih1 doing the work of elongating the spindle, which SGD already signals with the acts_upstream_of_or_within qualifier. Reason: Only the abstract is cached, and SGD read the full text; the phenotype is credible and consistent with Mih1 setting Cdc28-Clb2 activity during anaphase. It is a secondary consequence of the core Cdc28-activating role, not a core function. If refined, the mitotic child GO:0000022 (mitotic spindle elongation) would be the more precise term for this study. Supporting Evidence: PMID:30072442 Swe1 and the Polo-like kinase Cdc5 control the balance between phosphorylated and unphosphorylated forms of Mih1, which is, in turn, important for mitotic spindle elongation. PMID:30072442 Swe1 and Mih1 are both involved in controlling phosphorylation of Bik1. |
| GO:0110032 positive regulation of G2/MI transition of meiotic cell cycle | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Propagated from S. pombe cdc25, which triggers meiosis I by Cdc2-Tyr15 dephosphorylation. Budding-yeast data now support the same role for Mih1: after the meiotic recombination checkpoint is satisfied, meiosis I entry depends on removal of Cdc28-Tyr19 phosphorylation controlled by Swe1 versus Mih1, and Cdc5 promotes Mih1 nuclear entry at the prophase I to metaphase I transition. Reason: The node placement is correct and there is direct S. cerevisiae evidence (mih1 deletion produces a robust checkpoint-dependent prophase I arrest in zip1 cells). It is the same Cdc28-activating activity deployed in meiosis, so it is kept as a genuine but non-core role, matching the treatment of the S. pombe cdc25 review. Propagation Review Root cause: NO FAILURE NON CORE Sources checked: PANTHER:PTN000089071 SUPPORTS TRANSFER Current PAINT keeps the meiotic G2/MI assertion at the same Cdc25-family node. Budding-yeast Mih1 now has direct meiosis support, but this is a meiotic deployment of the same CDK-activating phosphatase activity rather than its core mitotic context. Supporting Evidence: PMID:41927924 meiosis I entry depends on removal of inhibitory phosphorylation controlled by the opposing activities of Swe1 and the Mih1 phosphatase PMID:41927924 the Mih1 phosphatase is essential for the eventual attenuation of checkpoint activity in zip1Ξ cells at later time points, allowing for the partial resumption of meiotic progression after a significant delay |
| GO:1902751 positive regulation of cell cycle G2/M phase transition | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO mapping from the MPI phosphatase family to the generic (mitotic or meiotic) G2/M positive-regulation term. Correct in substance, but the mitosis-specific child GO:0010971 is already assigned by IBA and is the term that describes Mih1's role. Reason: Prefer the more specific mitotic child term, as in the S. pombe cdc25 review; the generic parent adds no information beyond GO:0010971. Proposed replacements: positive regulation of G2/M transition of mitotic cell cycle Supporting Evidence: PMID:2649252 Expression of wee1+ in a mih1- strain prevents the initiation of mitosis. |
| GO:1905279 regulation of retrograde transport, endosome to Golgi | IDA PMID:28362258 A CDC25 family protein phosphatase gates cargo recognition b... | NEW | Summary: Proposed new annotation. Mih1 dephosphorylates the Vps26 retromer subunit in vivo and in vitro, and Vps26 phosphorylation state sets its affinity for retromer cargo and the sorting of that cargo at the endosome. Reason: Mih1 does the regulatory work itself: purified wild-type Mih1, but not the C320S catalytic mutant, dephosphorylates Vps26, and phosphomimetic and non-phosphorylatable Vps26 loop 6 substitutions change cargo binding and sorting. The term is the general regulation term because the paper reports effects in both directions (an activating mih1-1 allele and mih1 deletion) and does not settle the sign. It is not an ancestor or descendant of any term the gene carries. Non-core to the CDK-activating role. Supporting Evidence: PMID:28362258 The results clearly show that the wild-type and Mih1-1 phosphatases, but not Mih1(C320S), dephosphorylate Vps26 PMID:28362258 Thus, the data argue that Mih1 regulates retromer-dependent recycling in part by controlling the phosphorylation status of Vps26 loop 6 residues. |
Loading supporting contentβ¦
Download this section (compressed HTML)Q: Does Mih1 have physiological substrates other than Cdc28 Tyr19 (for example the Thr18 site, or non-CDK phosphoproteins such as Bik1), or is the Cdc25-family "dual specificity" not exploited in budding yeast?
Q: Which Mih1 phosphosites (casein kinase 1, Cdc5, Cdk1 targets) change catalytic activity versus nuclear import, and how does PP2A-Cdc55 dephosphorylation at mitotic entry alter Mih1 output mechanistically?
Q: Should the SGD ISS row for protein tyrosine phosphatase activity be upgraded to a direct-assay code now that purified Mih1 has been shown to dephosphorylate Swe1-phosphorylated Cdc28-Clb2 in vitro (Kennedy et al. 2016)?
Experiment: Substrate-trapping with a catalytically dead Mih1 (Cys320Ser) combined with phospho-tyrosine and phospho-threonine proteomics in synchronized mih1Ξ versus wild-type cells, to test whether Cdc28 Tyr19 is the only in vivo substrate.
Hypothesis: Mih1 is a dedicated Cdc28-Tyr19 phosphatase with no additional physiological substrates.
Experiment: Phosphosite-mutant series of Mih1 (CK1 and Cdc5 sites, singly and combined) assayed for in vitro activity toward Swe1-phosphorylated Cdc28-Clb2, nuclear accumulation kinetics by live imaging, and morphogenesis-checkpoint recovery timing, to separate catalytic from localization control.
Hypothesis: Interphase hyperphosphorylation restrains Mih1 mainly by limiting nuclear access rather than by lowering intrinsic phosphatase activity.
Loading supporting contentβ¦
Download this section (compressed HTML)Protein tyrosine phosphatase; involved in cell cycle control and retrograde protein transport; regulates the phosphorylation state of Cdc28p; modulates phosphorylation of retromer component Vps26p; homolog of S. pombe cdc25
Loading supporting contentβ¦
Download this section (compressed HTML)Loading supporting contentβ¦
Download this section (compressed HTML)