MEK-1 (NCU06419) is the MAP kinase kinase (MAPKK) of the Neurospora crassa MIK-1/MEK-1/MAK-1 cell wall integrity (CWI) MAPK cascade, orthologous to Saccharomyces cerevisiae Mkk1/Mkk2 and Schizosaccharomyces pombe Pek1/Skh1. It is a cytoplasmic serine/threonine/tyrosine (dual-specificity) protein kinase with a disordered N-terminal region (residues 1-142) and a C-terminal kinase domain (221-491) that retains the ATP-binding lysine and catalytic aspartate. MEK-1 is required for phosphorylation (activation) of the MAPK MAK-1. Loss of mek-1 reduces hyphal extension, abolishes macroconidiation and protoperithecium formation, weakens the cell wall (increased sensitivity to lytic enzymes and autolysis), derepresses tyrosinase expression under nitrogen starvation, and blocks germling (conidial anastomosis tube) fusion. Functional MEK-1-GFP accumulates, together with MIK-1 and MAK-1, at the contact sites of fusing germlings.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000165 MAPK cascade | IEA GO_REF:0000117 | MODIFY | Summary: Correct but general: MEK-1 acts in a MAPK cascade, specifically the MIK-1/MEK-1/MAK-1 cell wall integrity (CWI) cascade. Reason: MEK-1 is genetically required for phosphorylation of the CWI MAPK MAK-1 but not of the pheromone-response MAPK MAK-2, placing it in the cell integrity branch. GO:0000196 cell integrity MAPK cascade is an is_a descendant of GO:0000165 and is already carried by this gene (IBA and IEA rows), so the general term is refined to it. Proposed replacements: cell integrity MAPK cascade Supporting Evidence: PMID:18849472 phosphorylation of MAK-1 was not observed for the mik-1 and mek-1 deletion mutants under any growth conditions, indicating that MIK-1 and MEK-1 are required for the phosphorylation of MAK-1 PMID:41071819 All three MAP kinases of the MAK-1 kinase cascade localize at the contact site of fusing germlings. |
| GO:0000166 nucleotide binding | IEA GO_REF:0000104 | MODIFY | Summary: Correct but general: protein kinases bind ATP; the specific nucleotide is ATP. Reason: The kinase domain (Pfam PF00069) carries the PROSITE protein-kinase ATP-binding signature (K250 in the glycine-rich loop region). Nucleotide binding is true but less specific than GO:0005524 ATP binding, which the gene already carries; refine to that. Proposed replacements: ATP binding Supporting Evidence: file:NEUCR/mek-1/mek-1-uniprot.txt DR PROSITE; PS00107; PROTEIN_KINASE_ATP; 1. file:NEUCR/mek-1/mek-1-uniprot.txt DR Pfam; PF00069; Pkinase; 1. |
| GO:0000196 cell integrity MAPK cascade | IBA GO_REF:0000033 | ACCEPT | Summary: MEK-1 is the MAPKK tier of the Neurospora MIK-1/MEK-1/MAK-1 cell wall integrity cascade, homologous to S. cerevisiae Mkk1/Mkk2 and S. pombe Pek1/Skh1. Reason: The PAINT node PTN001220604 (donors include S. pombe Pek1 and the S. cerevisiae Mkk1/Mkk2 pair) covers the fungal CWI MAPKK clade; MEK-1 is placed in PANTHER subfamily PTHR47448:SF5 together with Pek1 and other filamentous-fungal Mkk1/Mkk2 orthologues, so it lies inside the clade. Neurospora experiments independently confirm the placement: MEK-1 is required for MAK-1 phosphorylation, and the deletion mutant shares the CWI cascade phenotypes (cell wall fragility, autolysis) with mik-1 and mak-1 mutants. Supporting Evidence: PMID:18849472 phosphorylation of MAK-1 was not observed for the mik-1 and mek-1 deletion mutants under any growth conditions, indicating that MIK-1 and MEK-1 are required for the phosphorylation of MAK-1 PMID:18849472 These results indicate that mik-1, mek-1 , and mak-1 are involved in the regulation of cell wall integrity in Neurospora . PMID:22900028 CWI-MAP kinase (Ξmik-1, Ξmek-1 and Ξmak-1) mutants showed rosette-like colony growth caused by areas of increased mycelial autolysis as typical features file:NEUCR/mek-1/mek-1-uniprot.txt DR PANTHER; PTHR47448:SF5; MITOGEN-ACTIVATED PROTEIN KINASE KINAE MKK2; 1. |
| GO:0000196 cell integrity MAPK cascade | IEA GO_REF:0000107 | ACCEPT | Summary: Ensembl Compara orthology transfer from S. pombe Pek1; consistent with the IBA row and with direct Neurospora data. Reason: Same claim as the IBA row; S. pombe Pek1 (Q9Y884) is in the same PANTHER subfamily (SF5) as MEK-1, and the Neurospora genetics (loss of MAK-1 phosphorylation in Ξmek-1) independently support it. Supporting Evidence: PMID:18849472 phosphorylation of MAK-1 was not observed for the mik-1 and mek-1 deletion mutants under any growth conditions, indicating that MIK-1 and MEK-1 are required for the phosphorylation of MAK-1 file:NEUCR/mek-1/mek-1-uniprot.txt DR PANTHER; PTHR47448:SF5; MITOGEN-ACTIVATED PROTEIN KINASE KINAE MKK2; 1. |
| GO:0000935 division septum | IEA GO_REF:0000107 | UNDECIDED | Summary: Compara transfer of a S. pombe Pek1 localization (division septum); no septal localization of MEK-1 has been reported in Neurospora. Reason: Pek1 and MEK-1 are true subfamily orthologues, so the transfer is evolutionarily sound in principle, but S. pombe medial division septa and the perforated cross-walls of Neurospora hyphae are not equivalent structures, and the only direct MEK-1-GFP imaging reports cytoplasmic signal with accumulation at germling contact sites, not at septa. Without target-specific localization data the claim can be neither confirmed nor refuted. Supporting Evidence: PMID:41071819 All three MAP kinases of the MAK-1 kinase cascade localize at the contact site of fusing germlings. |
| GO:0004672 protein kinase activity | IEA GO_REF:0000120 | MODIFY | Summary: Correct but general: MEK-1 is a MAP kinase kinase, a specific protein kinase. Reason: MEK-1 has an intact protein kinase domain (residues 221-491) with the ATP-binding lysine (K250) and catalytic HRD aspartate (D348), and is the MAPKK required for MAK-1 phosphorylation. protein kinase activity (GO:0004672) is an ancestor of GO:0004708 MAP kinase kinase activity, which the gene already carries (IBA/IEA), so the general term is refined to it. Proposed replacements: MAP kinase kinase activity Supporting Evidence: PMID:18849472 phosphorylation of MAK-1 was not observed for the mik-1 and mek-1 deletion mutants under any growth conditions, indicating that MIK-1 and MEK-1 are required for the phosphorylation of MAK-1 file:NEUCR/mek-1/mek-1-uniprot.txt DR InterPro; IPR050915; MAP_kinase_kinase. file:NEUCR/mek-1/mek-1-uniprot.txt DR Pfam; PF00069; Pkinase; 1. |
| GO:0004674 protein serine/threonine kinase activity | IEA GO_REF:0000120 | MODIFY | Summary: MAP kinase kinases are dual-specificity kinases phosphorylating the Thr and Tyr of the MAPK TXY motif; serine/threonine kinase activity alone mis-describes the activity class. Reason: The row derives from the generic PROSITE Ser/Thr kinase active-site signature and EC 2.7.11.1. Members of the MAPKK subfamily (InterPro IPR050915) phosphorylate both the threonine and tyrosine of the MAPK activation loop, and GO:0004708 MAP kinase kinase activity is classified under GO:0004712 protein serine/threonine/tyrosine kinase activity, not under GO:0004674. Replace with GO:0004708, which the gene already carries. Direct biochemical demonstration of MEK-1 phosphorylating MAK-1 in vitro is lacking; the activity rests on the Neurospora genetic dependence of MAK-1 phosphorylation plus phylogenetic placement. Proposed replacements: MAP kinase kinase activity Supporting Evidence: PMID:18849472 phosphorylation of MAK-1 was not observed for the mik-1 and mek-1 deletion mutants under any growth conditions, indicating that MIK-1 and MEK-1 are required for the phosphorylation of MAK-1 file:NEUCR/mek-1/mek-1-uniprot.txt DR InterPro; IPR050915; MAP_kinase_kinase. |
| GO:0004707 MAP kinase activity | IEA GO_REF:0000003 | REMOVE | Summary: EC 2.7.11.24 (MAP kinase) mapping is wrong for this protein: MEK-1 is the MAPKK upstream of the MAPK MAK-1, not itself a MAP kinase. Reason: Full re-review (2026-10-21): this is a demonstrably wrong EC-to-GO mapping, so REMOVE rather than MODIFY. EC 2.7.11.24 reached the record only through ARBA-assigned catalytic-activity lines (ARBA00048130/ARBA00047919). GO:0004707 MAP kinase activity defines the MAPK tier (a kinase that is itself activated by MAPKK phosphorylation of a TXY motif); MEK-1 is the MAPKK that acts upstream of the MAPK MAK-1, belongs to the STE7/MAP kinase kinase family (InterPro IPR050915), and lacks the CMGC MAPK fold and TXY activation motif. GO:0004708 is not an is_a descendant of GO:0004707, so this is not a refinement; the correct activity is already carried by this gene on independent IBA and Compara rows. Supporting Evidence: PMID:18849472 The MAK-1 MAPK was not phosphorylated in Ξ mik-1 and Ξ mek-1 mutants, consistent with the involvement of MIK-1, MEK-1, and MAK-1 in the same signaling cascade. file:NEUCR/mek-1/mek-1-uniprot.txt DR InterPro; IPR050915; MAP_kinase_kinase. |
| GO:0004708 MAP kinase kinase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Core activity: MEK-1 is the MAP kinase kinase that activates MAK-1. Reason: PAINT node PTN000684494 places MAPKK activity at the root of the MAPKK family, with experimental donors across fungi, animals and plants; MEK-1 (PTHR47448:SF5, InterPro MAP_kinase_kinase) is inside that clade and retains the catalytic residues. Neurospora experiments show MEK-1 is required for MAK-1 phosphorylation. Note that the PANTHER parent family boundary (PTHR47448 versus PTHR48013) is unresolved in the repo family review, but both placements put MEK-1 in the same subfamily as S. pombe Pek1, so the MAPKK grant is unaffected. On re-review (2026-10-21), in UniProt cross-references MEK-1 and Pek1 (Q9Y884) are both PTHR47448:SF5, while PANTHER's own per-organism classification places MEK-1 and Pek1 in PTHR48013:SF6 (MAP KINASE KINASE MKK1_SSP32-RELATED), the same subfamily that UniProt gives for S. cerevisiae Mkk1 (P32490) and Mkk2 (P32491). Under either source the CWI MAPKK donors co-segregate with MEK-1. Supporting Evidence: PMID:18849472 phosphorylation of MAK-1 was not observed for the mik-1 and mek-1 deletion mutants under any growth conditions, indicating that MIK-1 and MEK-1 are required for the phosphorylation of MAK-1 file:NEUCR/mek-1/mek-1-uniprot.txt DR InterPro; IPR050915; MAP_kinase_kinase. file:NEUCR/mek-1/mek-1-uniprot.txt DR PANTHER; PTHR47448:SF5; MITOGEN-ACTIVATED PROTEIN KINASE KINAE MKK2; 1. |
| GO:0004708 MAP kinase kinase activity | IEA GO_REF:0000107 | ACCEPT | Summary: Compara transfer from S. pombe Pek1; same claim as the IBA row. Reason: Consistent with the IBA row and the Neurospora genetic data; Pek1 is a same-subfamily orthologue. Supporting Evidence: PMID:18849472 phosphorylation of MAK-1 was not observed for the mik-1 and mek-1 deletion mutants under any growth conditions, indicating that MIK-1 and MEK-1 are required for the phosphorylation of MAK-1 file:NEUCR/mek-1/mek-1-uniprot.txt DR PANTHER; PTHR47448:SF5; MITOGEN-ACTIVATED PROTEIN KINASE KINAE MKK2; 1. |
| GO:0005524 ATP binding | IEA GO_REF:0000120 | KEEP AS NON CORE | Summary: MEK-1 has the protein kinase ATP-binding site required for phosphotransfer. Reason: ATP binding is true and as precise as warranted (PROSITE PS00107 ATP-binding signature, K250), but it is a cofactor-binding property of every active kinase and is entailed by the core MAPKK activity rather than being a distinct function. Supporting Evidence: file:NEUCR/mek-1/mek-1-uniprot.txt DR PROSITE; PS00107; PROTEIN_KINASE_ATP; 1. file:NEUCR/mek-1/mek-1-uniprot.txt DR Pfam; PF00069; Pkinase; 1. |
| GO:0005737 cytoplasm | IEA GO_REF:0000107 | ACCEPT | Summary: MEK-1-GFP is cytoplasmic and accumulates at germling contact sites, consistent with a soluble cytoplasmic MAPK module component. Reason: Compara transfer from S. pombe Pek1 is consistent with direct Neurospora imaging of functional MEK-1-GFP (complementing Ξmek-1), which shows it together with MIK-1 and MAK-1 at the contact sites of fusing germlings. MEK-1 has no transmembrane segment or signal peptide, and the contact-site pool is cortical cytoplasm. Cytoplasm is the most precise GO location currently supported. Supporting Evidence: PMID:41071819 All three MAP kinases of the MAK-1 kinase cascade localize at the contact site of fusing germlings. |
| GO:0016301 kinase activity | IEA GO_REF:0000104 | MODIFY | Summary: Correct but general: MEK-1 is a MAP kinase kinase, a specific protein kinase. Reason: MEK-1 has an intact protein kinase domain (residues 221-491) with the ATP-binding lysine (K250) and catalytic HRD aspartate (D348), and is the MAPKK required for MAK-1 phosphorylation. kinase activity (GO:0016301) is an ancestor of GO:0004708 MAP kinase kinase activity, which the gene already carries (IBA/IEA), so the general term is refined to it. Proposed replacements: MAP kinase kinase activity Supporting Evidence: PMID:18849472 phosphorylation of MAK-1 was not observed for the mik-1 and mek-1 deletion mutants under any growth conditions, indicating that MIK-1 and MEK-1 are required for the phosphorylation of MAK-1 file:NEUCR/mek-1/mek-1-uniprot.txt DR InterPro; IPR050915; MAP_kinase_kinase. file:NEUCR/mek-1/mek-1-uniprot.txt DR Pfam; PF00069; Pkinase; 1. |
| GO:0016740 transferase activity | IEA GO_REF:0000104 | MODIFY | Summary: Correct but general: MEK-1 is a MAP kinase kinase, a specific protein kinase. Reason: MEK-1 has an intact protein kinase domain (residues 221-491) with the ATP-binding lysine (K250) and catalytic HRD aspartate (D348), and is the MAPKK required for MAK-1 phosphorylation. transferase activity (GO:0016740) is an ancestor of GO:0004708 MAP kinase kinase activity, which the gene already carries (IBA/IEA), so the general term is refined to it. Proposed replacements: MAP kinase kinase activity Supporting Evidence: PMID:18849472 phosphorylation of MAK-1 was not observed for the mik-1 and mek-1 deletion mutants under any growth conditions, indicating that MIK-1 and MEK-1 are required for the phosphorylation of MAK-1 file:NEUCR/mek-1/mek-1-uniprot.txt DR InterPro; IPR050915; MAP_kinase_kinase. file:NEUCR/mek-1/mek-1-uniprot.txt DR Pfam; PF00069; Pkinase; 1. |
| GO:0050850 positive regulation of calcium-mediated signaling | IEA GO_REF:0000107 | UNDECIDED | Summary: Compara transfer of a S. pombe Pek1-specific regulatory role in calcium/calcineurin signalling; no Neurospora evidence. Reason: The relationship to Pek1 is a true subfamily orthology, but this term reflects S. pombe-specific cross-talk between the Pmk1 cascade and calcineurin signalling. In Neurospora, loss of mek-1 did not alter sensitivity to the calcineurin inhibitor FK506, which provides no support (though does not refute) a conserved positive role in calcium-mediated signalling. Pending target-specific data, leave undecided. Supporting Evidence: PMID:18849472 This demonstrates that the loss of mik-1, mek-1 , or mak-1 does not significantly affect sensitivity to hydrogen peroxide, aculeacin A, or FK-506 in Neurospora . |
| GO:0060237 regulation of fungal-type cell wall organization | IBA GO_REF:0000033 | ACCEPT | Summary: The CWI cascade controls fungal cell wall organization; Ξmek-1 mutants have fragile cell walls and autolyse. Reason: PAINT node PTN001220604 (Mkk1/Mkk2, Pek1 donors) covers MEK-1. Neurospora Ξmek-1 conidia and hyphae are hypersensitive to cell wall lytic enzymes and mutant colonies show autolysis, consistent with MEK-1 acting via the cascade in regulating cell wall organization. The phenotype is milder than in budding yeast, so this is a real but partial role. Supporting Evidence: PMID:18849472 These results indicate that mik-1, mek-1 , and mak-1 are involved in the regulation of cell wall integrity in Neurospora . PMID:22900028 CWI-MAP kinase (Ξmik-1, Ξmek-1 and Ξmak-1) mutants showed rosette-like colony growth caused by areas of increased mycelial autolysis as typical features |
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Download this section (compressed HTML)Q: Does MEK-1 directly phosphorylate both the Thr and Tyr of the MAK-1 TEY activation motif, and does MIK-1 phosphorylate the MEK-1 activation loop?
Q: Is the S. pombe Pek1 link to calcium/calcineurin signalling and division-septum localization conserved for Neurospora MEK-1, given that Ξmek-1 is not FK506-hypersensitive?
Experiment: In vitro kinase assay with purified MEK-1 (wild type and K250R) and kinase-dead MAK-1 substrate, with phospho-site mapping of the TEY motif.
Experiment: Live imaging of functional MEK-1-GFP in mature hyphae to test for septal accumulation.
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