id: P34208
gene_symbol: chk1
product_type: PROTEIN
status: DRAFT
taxon:
  id: NCBITaxon:284812
  label: Schizosaccharomyces pombe (strain 972 / ATCC 24843)
description: >-
  Chk1 is the effector serine/threonine protein kinase (EC 2.7.11.1) of the G2/M
  DNA-damage checkpoint in the fission yeast Schizosaccharomyces pombe. In
  response to DNA damage or unligated/unreplicated DNA, Chk1 is phosphorylated at
  Ser-345 and activated by the ATR-related checkpoint kinase Rad3, acting together
  with the 9-1-1 (Rad9-Rad1-Hus1) clamp, the clamp loader Rad17, Rad4/Cut5, and
  the BRCT-domain mediator Crb2 (a 53BP1-like protein) that recruits Chk1 to
  double-strand breaks. Activated Chk1 phosphorylates and inhibits the mitotic
  inducer phosphatase Cdc25 (promoting its 14-3-3 binding) and phosphorylates the
  Cdc2-Y15 kinase Wee1, thereby maintaining inhibitory tyrosine-15 phosphorylation
  of Cdc2/CDK1 and blocking mitotic entry to enforce a G2 arrest. Chk1 is the
  DNA-damage-branch counterpart of Cds1, the DNA-replication checkpoint effector
  kinase; the two act redundantly to phosphorylate Cdc25 at the replication
  checkpoint. Beyond mitotic G2 arrest, Chk1 contributes to a G1-phase checkpoint,
  represses MBF-dependent S-phase gene transcription by phosphorylating the MBF
  core subunit Cdc10, and participates in a meiotic recombination checkpoint that
  restrains meiotic prophase progression. Chk1 is a nuclear kinase that forms foci
  at sites of DNA double-strand breaks.
references:
- id: file:interpro/panther/PTHR43895/PTHR43895-review.md
  title: 'PANTHER family review PTHR43895: IBA propagation assessment for chk1'
  findings: []
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO
    terms
  findings: []
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000044
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location
    vocabulary mapping, accompanied by conservative changes to GO terms applied by
    UniProt
  findings: []
- id: GO_REF:0000116
  title: Automatic Gene Ontology annotation based on Rhea mapping
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:10825192
  title: Mechanism of caffeine-induced checkpoint override in fission yeast.
  findings:
  - statement: Caffeine inhibits Rad3, blocking phosphorylation of Chk1 and activation
      of Cds1, thereby overriding both the S-M replication and G2-M DNA damage checkpoints.
      Chk1 is regulated by Rad3.
    supporting_text: Caffeine prevented activation of Cds1 and phosphorylation of Chk1,
      two protein kinases that enforce the S-M checkpoint triggered by hydroxyurea.
      Caffeine did not inhibit these kinases in vitro but did inhibit Rad3, a kinase
      that regulates Cds1 and Chk1.
    reference_section_type: ABSTRACT
- id: PMID:11553781
  title: Serine-345 is required for Rad3-dependent phosphorylation and function of
    checkpoint kinase Chk1 in fission yeast.
  findings:
  - statement: Rad3 phosphorylates Chk1 on Ser-345; this modification is required for
      the G2-M DNA damage checkpoint and for survival of DNA damage.
    supporting_text: Rad3 and ATM phosphorylate serine-345 of fission yeast Chk1. Mutation
      of serine-345 (chk1-S345A) abrogates Rad3-dependent phosphorylation of Chk1
      in vivo. The chk1-S345A cells are sensitive to DNA damage and are checkpoint
      defective.
    reference_section_type: ABSTRACT
- id: PMID:12186947
  title: A novel chk1-dependent G1/M checkpoint in fission yeast.
  findings:
  - statement: Chk1 is required for a G1-phase checkpoint arrest in pre-replicative
      complex (orp1-4) mutant cells, acting to induce/maintain inhibitory Cdc2 phosphorylation.
    supporting_text: The arrest depends upon the checkpoint Rad proteins and, surprisingly,
      the Chk1 protein, which is thought to act only from late S phase.
    reference_section_type: ABSTRACT
- id: PMID:14739927
  title: Regulation of checkpoint kinases through dynamic interaction with Crb2.
  findings:
  - statement: Crb2 dynamically interacts with both Rad3 and Chk1; Chk1 activation
      in vitro requires the Crb2 BRCT domain.
    supporting_text: Crb2 regulates DNA damage checkpoint through temporal and dynamic
      interactions with Rad3, Chk1 and replication factor Cut5.
    reference_section_type: ABSTRACT
- id: PMID:15229228
  title: 'Homo-oligomerization is the essential function of the tandem BRCT domains in the checkpoint protein Crb2.'
  findings: []
- id: PMID:16823372
  title: ORFeome cloning and global analysis of protein localization in the fission
    yeast Schizosaccharomyces pombe.
  findings: []
- id: PMID:17502373
  title: Fission yeast Rnf4 homologs are required for DNA repair.
  findings:
  - statement: Rfp1 (an Rnf4/RING-finger homolog) was isolated as a Chk1-interacting
      protein in a two-hybrid screen; rfp1/rfp2 act in DNA repair but checkpoint signaling
      to Chk1 is normal in their absence.
    supporting_text: Rfp1 was isolated as a Chk1-interacting protein in a two-hybrid
      screen and has high amino acid sequence similarity to Rfp2.
    reference_section_type: ABSTRACT
- id: PMID:22792081
  title: Phosphorylation-dependent interactions between Crb2 and Chk1 are essential
    for DNA damage checkpoint.
  findings:
  - statement: Crb2 recruits Chk1 to double-strand breaks via a direct phospho-dependent
      interaction; Chk1 forms nuclear foci at DSBs that colocalize with Crb2/Rad22.
    supporting_text: Crb2 recruits Chk1 to double-strand breaks (DSBs) through a direct
      physical interaction.
    reference_section_type: ABSTRACT
- id: PMID:24006488
  title: The DNA damage and the DNA replication checkpoints converge at the MBF transcription
    factor.
  findings:
  - statement: Upon DNA damage Chk1 phosphorylates the MBF core subunit Cdc10, releasing
      MBF from chromatin and repressing S-phase gene transcription.
    supporting_text: Chk1 is activated and phosphorylates Cdc10 at its carboxy-terminal
      domain. This modification is responsible for the repression of MBF-dependent
      transcription through induced release of MBF from chromatin.
    reference_section_type: ABSTRACT
- id: PMID:25533348
  title: Tolerance of deregulated G1/S transcription depends on critical G1/S regulon
    genes to prevent catastrophic genome instability.
  findings: []
- id: PMID:26131711
  title: Two Distinct Cdc2 Pools Regulate Cell Cycle Progression and the DNA Damage
    Response in the Fission Yeast S.pombe.
  findings: []
- id: PMID:29123917
  title: The telomere bouquet facilitates meiotic prophase progression and exit in
    fission yeast.
  findings:
  - statement: Persistent meiotic recombination DNA damage activates the Rad3-Chk1
      checkpoint to extend the telomere bouquet/meiotic prophase stage.
    supporting_text: Persistent DNA damages, induced during meiotic recombination,
      activate the Rad3 and Chk1 DNA damage checkpoint kinases and extend the bouquet
      stage beyond the chromosome oscillation period.
    reference_section_type: ABSTRACT
- id: PMID:8497322
  title: Fission yeast chk1 protein kinase links the rad checkpoint pathway to cdc2.
  findings:
  - statement: chk1 encodes a protein kinase required for cell-cycle arrest in response
      to DNA damage or unligated DNA, linking the rad checkpoint pathway to cdc2.
    supporting_text: we have identified a novel fission yeast protein kinase homologue
      which is involved in cell-cycle arrest when DNA damage has occurred or when unligated
      DNA is present. We have called the gene encoding this protein chk1 for checkpoint
      kinase.
    reference_section_type: ABSTRACT
- id: PMID:9034337
  title: Chk1 is a wee1 kinase in the G2 DNA damage checkpoint inhibiting cdc2 by Y15
    phosphorylation.
  findings:
  - statement: Chk1 directly phosphorylates Wee1 in vitro and in vivo, maintaining
      inhibitory Cdc2-Y15 phosphorylation and G2 delay.
    supporting_text: p56chk1 can phosphorylate p107wee1 directly in vitro. These observations
      suggest that in response to DNA damage p107wee1 is phosphorylated by p56chk1
      in vivo, and this results in maintenance of Y15 phosphorylation and hence G2
      delay.
    reference_section_type: ABSTRACT
- id: PMID:9042863
  title: Cdc2 tyrosine phosphorylation is required for the DNA damage checkpoint in
    fission yeast.
  findings:
  - statement: The G2 DNA damage checkpoint arrest depends on inhibitory Cdc2 tyrosine-15
      phosphorylation carried out by Wee1 and Mik1.
    supporting_text: the G2 DNA damage checkpoint arrest in S. pombe depends on the
      inhibitory tyrosine phosphorylation of Cdc2 carried out by the Wee1 and Mik1
      kinases.
    reference_section_type: ABSTRACT
- id: PMID:9278510
  title: Cdc25 mitotic inducer targeted by chk1 DNA damage checkpoint kinase.
  findings:
  - statement: Chk1 binds and phosphorylates Cdc25, identifying Cdc25 (not Wee1) as
      the target of the DNA damage checkpoint that prevents mitotic entry.
    supporting_text: Cdc25 associated with Chk1 in vivo and was phosphorylated when
      copurified in Chk1 complexes. These findings identify Cdc25, but not Wee1, as
      a target of the DNA damage checkpoint.
    reference_section_type: ABSTRACT
- id: PMID:9774107
  title: Replication checkpoint requires phosphorylation of the phosphatase Cdc25
    by Cds1 or Chk1.
  findings:
  - statement: Chk1 and Cds1 act redundantly at the replication checkpoint, both phosphorylating
      Cdc25 on the same residues to promote 14-3-3 binding and prevent Cdc2 activation.
    supporting_text: Chk1 functions redundantly with the kinase Cds1 at the replication
      checkpoint and that both kinases phosphorylate Cdc25 on the same sites, which
      include serine residues at positions 99, 192 and 359.
    reference_section_type: ABSTRACT
- id: Reactome:R-SPO-75040
  title: Phosphorylation of Wee1 kinase by Chk1
  findings: []
existing_annotations:
- term:
    id: GO:0005634
    label: nucleus
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: Chk1 is a nuclear kinase; this is its site of action where it is activated
      by Rad3 and phosphorylates nuclear substrates (Cdc25, Wee1, Cdc10). Phylogenetic
      inference is consistent with direct experimental nuclear localization.
    action: ACCEPT
    reason: Nuclear localization is supported experimentally (IDA, HDA) and by UniProt
      subcellular location, consistent with Chk1's function in the nucleus.
    supported_by:
    - reference_id: PMID:11553781
      supporting_text: This checkpoint is enforced by Chk1, a protein kinase that inhibits
        the mitotic inducer Cdc25.
      reference_section_type: ABSTRACT
- term:
    id: GO:0007095
    label: mitotic G2 DNA damage checkpoint signaling
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: This is the core biological process of Chk1 as the effector kinase of
      the G2/M DNA damage checkpoint. Strongly supported by phylogenetic inference
      and abundant experimental evidence.
    action: ACCEPT
    reason: Core function; corroborated by multiple experimental annotations (IDA/IMP/EXP).
    supported_by:
    - reference_id: PMID:8497322
      supporting_text: we have identified a novel fission yeast protein kinase homologue
        which is involved in cell-cycle arrest when DNA damage has occurred or when
        unligated DNA is present. We have called the gene encoding this protein chk1
        for checkpoint kinase.
      reference_section_type: ABSTRACT
- term:
    id: GO:0035861
    label: site of double-strand break
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: Chk1 is recruited to and active at sites of DNA double-strand breaks,
      where it is activated by Rad3 via the Crb2 mediator; Chk1-GFP forms foci colocalizing
      with Crb2/Rad22 at DSBs. Phylogenetic inference matches the experimental IDA.
    action: ACCEPT
    reason: Recruitment to DSBs is directly demonstrated experimentally and consistent
      with phylogenetic inference.
    supported_by:
    - reference_id: PMID:22792081
      supporting_text: Crb2 recruits Chk1 to double-strand breaks (DSBs) through a
        direct physical interaction.
      reference_section_type: ABSTRACT
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: A cytoplasmic pool is reported by high-throughput and IDA localization,
      but Chk1's documented function (activation by Rad3, phosphorylation of Cdc25/Wee1/Cdc10,
      DSB foci) is nuclear. The cytoplasmic localization is not a site of established
      function.
    action: KEEP_AS_NON_CORE
    reason: Cytoplasmic localization is observed but does not correspond to Chk1's
      site of action, which is nuclear; retain as non-core context.
    supported_by:
    - reference_id: PMID:11553781
      supporting_text: This checkpoint is enforced by Chk1, a protein kinase that inhibits
        the mitotic inducer Cdc25.
      reference_section_type: ABSTRACT
- term:
    id: GO:0000077
    label: DNA damage checkpoint signaling
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: involved_in
  review:
    summary: General DNA damage checkpoint signaling is correct for Chk1 and is the
      parent of the more specific mitotic G2 DNA damage checkpoint signaling term that
      is also annotated. Accepted as a correct, if less specific, process term.
    action: ACCEPT
    reason: Correct process; the more specific GO:0007095 is preferred for representing
      the core function but this parent term is not wrong.
    supported_by:
    - reference_id: PMID:8497322
      supporting_text: we have identified a novel fission yeast protein kinase homologue
        which is involved in cell-cycle arrest when DNA damage has occurred or when
        unligated DNA is present.
      reference_section_type: ABSTRACT
- term:
    id: GO:0004672
    label: protein kinase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: Chk1 is a protein kinase; this InterPro-based term is correct but is a
      general parent of the experimentally supported protein serine/threonine kinase
      activity.
    action: MODIFY
    reason: The essence is correct but a more specific child term (protein serine/threonine
      kinase activity) is experimentally supported and preferred.
    proposed_replacement_terms:
    - id: GO:0004674
      label: protein serine/threonine kinase activity
    supported_by:
    - reference_id: PMID:9034337
      supporting_text: p56chk1 can phosphorylate p107wee1 directly in vitro.
      reference_section_type: ABSTRACT
- term:
    id: GO:0004674
    label: protein serine/threonine kinase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: enables
  review:
    summary: Core molecular function. Chk1 is a Ser/Thr protein kinase (EC 2.7.11.1)
      that phosphorylates Cdc25, Wee1, and Cdc10. Supported by IEA and multiple direct
      experimental assays.
    action: ACCEPT
    reason: Core catalytic function, supported by direct in vitro kinase assays.
    supported_by:
    - reference_id: PMID:9034337
      supporting_text: p56chk1 can phosphorylate p107wee1 directly in vitro.
      reference_section_type: ABSTRACT
- term:
    id: GO:0005524
    label: ATP binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: As an active protein kinase with a conserved ATP-binding P-loop (residues
      16-24, 38), ATP binding is a correct and expected molecular function.
    action: ACCEPT
    reason: Supported by the conserved protein kinase domain and ATP-binding motif
      in the sequence.
    supported_by:
    - reference_id: PMID:9034337
      supporting_text: p56chk1 can phosphorylate p107wee1 directly in vitro.
      reference_section_type: ABSTRACT
- term:
    id: GO:0005634
    label: nucleus
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: Nuclear localization from UniProt subcellular location mapping; consistent
      with experimental localization and Chk1's nuclear function.
    action: ACCEPT
    reason: Redundant with the experimental nucleus annotation but correct.
    supported_by:
    - reference_id: PMID:11553781
      supporting_text: This checkpoint is enforced by Chk1, a protein kinase that inhibits
        the mitotic inducer Cdc25.
      reference_section_type: ABSTRACT
- term:
    id: GO:0106310
    label: protein serine kinase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000116
  qualifier: enables
  review:
    summary: Rhea/EC-based term capturing serine phosphorylation activity; correct
      and consistent with the broader protein serine/threonine kinase activity.
    action: ACCEPT
    reason: Correct molecular function consistent with EC 2.7.11.1.
    supported_by:
    - reference_id: PMID:9034337
      supporting_text: p56chk1 can phosphorylate p107wee1 directly in vitro.
      reference_section_type: ABSTRACT
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:14739927
  qualifier: enables
  review:
    summary: This IPI captures the Chk1-Crb2 interaction. The bare protein binding
      term is uninformative; the meaningful function is Chk1's regulated interaction
      with the BRCT-mediator Crb2 that is required for Chk1 activation.
    action: MARK_AS_OVER_ANNOTATED
    reason: Bare protein binding is uninformative per curation guidelines; the underlying
      Crb2 interaction is better captured by the checkpoint signaling process terms.
    supported_by:
    - reference_id: PMID:14739927
      supporting_text: Crb2 regulates DNA damage checkpoint through temporal and dynamic
        interactions with Rad3, Chk1 and replication factor Cut5.
      reference_section_type: ABSTRACT
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:15229228
  qualifier: enables
  review:
    summary: A protein binding IPI annotation referencing PMID:15229228, which is not
      available in the cached publications, so the specific interaction partner and
      its significance cannot be verified.
    action: UNDECIDED
    reason: The supporting publication (PMID:15229228) could not be accessed; bare
      protein binding is in any case uninformative.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:17502373
  qualifier: enables
  review:
    summary: Captures the Chk1-Rfp1 two-hybrid interaction. Bare protein binding is
      uninformative, and rfp1/rfp2 mutants retain normal checkpoint signaling to Chk1,
      so this interaction is not part of Chk1's core checkpoint function.
    action: MARK_AS_OVER_ANNOTATED
    reason: Uninformative bare protein binding; the interaction is peripheral (DNA
      repair/SUMO context) rather than core to Chk1 function.
    supported_by:
    - reference_id: PMID:17502373
      supporting_text: Rfp1 was isolated as a Chk1-interacting protein in a two-hybrid
        screen and has high amino acid sequence similarity to Rfp2.
      reference_section_type: ABSTRACT
- term:
    id: GO:0004674
    label: protein serine/threonine kinase activity
  evidence_type: TAS
  original_reference_id: Reactome:R-SPO-75040
  qualifier: enables
  review:
    summary: Reactome annotation (Phosphorylation of Wee1 kinase by Chk1) supporting
      Chk1's Ser/Thr kinase activity. Correct core molecular function.
    action: ACCEPT
    reason: Consistent with experimentally demonstrated kinase activity toward Wee1.
    supported_by:
    - reference_id: PMID:9034337
      supporting_text: p56chk1 can phosphorylate p107wee1 directly in vitro.
      reference_section_type: ABSTRACT
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:22792081
  qualifier: enables
  review:
    summary: Captures the phosphorylation-dependent Chk1-Crb2 interaction at DSBs.
      Bare protein binding is uninformative; the functional significance is recruitment
      of Chk1 to DSBs for activation.
    action: MARK_AS_OVER_ANNOTATED
    reason: Bare protein binding term is uninformative; the biology is better captured
      by the DSB localization and checkpoint signaling annotations.
    supported_by:
    - reference_id: PMID:22792081
      supporting_text: Crb2 recruits Chk1 to double-strand breaks (DSBs) through a
        direct physical interaction.
      reference_section_type: ABSTRACT
- term:
    id: GO:0007095
    label: mitotic G2 DNA damage checkpoint signaling
  evidence_type: IMP
  original_reference_id: PMID:22792081
  qualifier: involved_in
  review:
    summary: Direct genetic/cell-biological evidence that Chk1 acts in the G2 DNA damage
      checkpoint, with its recruitment and activation at DSBs required for checkpoint
      arrest. Core function.
    action: ACCEPT
    reason: Core function supported by mutant phenotype analysis (crb2 SQ/TQ mutants
      abolish Chk1 activation and checkpoint arrest).
    supported_by:
    - reference_id: PMID:22792081
      supporting_text: A pair of conserved SQ/TQ motifs in Crb2, which are consensus
        phosphorylation sites of upstream kinase Rad3, is required for Chk1 recruitment
        and activation.
      reference_section_type: ABSTRACT
- term:
    id: GO:0004674
    label: protein serine/threonine kinase activity
  evidence_type: IDA
  original_reference_id: PMID:9034337
  qualifier: enables
  review:
    summary: Direct in vitro demonstration of Chk1 Ser/Thr kinase activity, phosphorylating
      Wee1. Core molecular function.
    action: ACCEPT
    reason: Direct experimental assay of kinase activity.
    supported_by:
    - reference_id: PMID:9034337
      supporting_text: p56chk1 can phosphorylate p107wee1 directly in vitro.
      reference_section_type: ABSTRACT
- term:
    id: GO:0007095
    label: mitotic G2 DNA damage checkpoint signaling
  evidence_type: IDA
  original_reference_id: PMID:9034337
  qualifier: involved_in
  review:
    summary: Chk1 overexpression and UV-induced delay depend on Wee1, with Chk1 phosphorylating
      Wee1 to maintain Cdc2-Y15 phosphorylation and G2 delay. Core function.
    action: ACCEPT
    reason: Core checkpoint function demonstrated through the Chk1-Wee1-Cdc2 axis.
    supported_by:
    - reference_id: PMID:9034337
      supporting_text: wee1 is required for cell cycle arrest induced by up-regulation
        of an essential component of this checkpoint, chk1.
      reference_section_type: ABSTRACT
- term:
    id: GO:0051598
    label: meiotic recombination checkpoint signaling
  evidence_type: IMP
  original_reference_id: PMID:29123917
  qualifier: involved_in
  review:
    summary: Chk1 (with Rad3) responds to persistent meiotic recombination DNA damage
      to restrain meiotic prophase exit (the post-horsetail bouquet stage). A specialized,
      non-core role distinct from the mitotic checkpoint.
    action: KEEP_AS_NON_CORE
    reason: Genuine but specialized meiotic function; not the defining mitotic checkpoint
      role of Chk1.
    supported_by:
    - reference_id: PMID:29123917
      supporting_text: Persistent DNA damages, induced during meiotic recombination,
        activate the Rad3 and Chk1 DNA damage checkpoint kinases and extend the bouquet
        stage beyond the chromosome oscillation period.
      reference_section_type: ABSTRACT
- term:
    id: GO:0004674
    label: protein serine/threonine kinase activity
  evidence_type: IDA
  original_reference_id: PMID:9774107
  qualifier: enables
  review:
    summary: Chk1 phosphorylates Cdc25 (at S99, S192, S359), demonstrating Ser/Thr
      kinase activity on a physiological substrate. Core molecular function.
    action: ACCEPT
    reason: Direct evidence of kinase activity toward Cdc25.
    supported_by:
    - reference_id: PMID:9774107
      supporting_text: both kinases phosphorylate Cdc25 on the same sites, which include
        serine residues at positions 99, 192 and 359.
      reference_section_type: ABSTRACT
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:9278510
  qualifier: enables
  review:
    summary: Captures the Chk1-Cdc25 interaction (Cdc25 copurifies with and is phosphorylated
      by Chk1). Bare protein binding is uninformative; the meaningful relationship
      is Chk1's kinase-substrate action on Cdc25.
    action: MARK_AS_OVER_ANNOTATED
    reason: Bare protein binding is uninformative; the Cdc25 interaction is better
      represented by Chk1's kinase activity and checkpoint signaling annotations.
    supported_by:
    - reference_id: PMID:9278510
      supporting_text: Cdc25 associated with Chk1 in vivo and was phosphorylated when
        copurified in Chk1 complexes.
      reference_section_type: ABSTRACT
- term:
    id: GO:0006281
    label: DNA repair
  evidence_type: EXP
  original_reference_id: PMID:8497322
  qualifier: involved_in
  negated: true
  review:
    summary: Correctly negated. Chk1 is a checkpoint signaling kinase that arrests
      the cell cycle in response to damage but does not itself carry out DNA repair.
    action: ACCEPT
    reason: The NOT annotation appropriately distinguishes checkpoint signaling from
      the repair machinery; Chk1 signals arrest, it does not repair DNA.
    supported_by:
    - reference_id: PMID:8497322
      supporting_text: we have identified a novel fission yeast protein kinase homologue
        which is involved in cell-cycle arrest when DNA damage has occurred or when
        unligated DNA is present.
      reference_section_type: ABSTRACT
- term:
    id: GO:0007095
    label: mitotic G2 DNA damage checkpoint signaling
  evidence_type: EXP
  original_reference_id: PMID:8497322
  qualifier: involved_in
  review:
    summary: Original identification of chk1 as the checkpoint kinase required for
      cell-cycle arrest after DNA damage. Core function.
    action: ACCEPT
    reason: Foundational experimental evidence for Chk1's core checkpoint role.
    supported_by:
    - reference_id: PMID:8497322
      supporting_text: We have called the gene encoding this protein chk1 for checkpoint
        kinase.
      reference_section_type: ABSTRACT
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:26131711
  qualifier: enables
  review:
    summary: A protein binding IPI annotation arising from a study of Cdc2 phospho-forms
      and the DNA damage response. Bare protein binding is uninformative and the specific
      interaction is not a defining Chk1 function.
    action: MARK_AS_OVER_ANNOTATED
    reason: Uninformative bare protein binding term; not central to Chk1's characterized
      function.
    supported_by:
    - reference_id: PMID:26131711
      supporting_text: The activity of Cdc2 (CDK1) kinase, which coordinates cell cycle
        progression and DNA break repair, is blocked upon its phosphorylation at tyrosine
        15 (Y15) by Wee1 kinase in the presence of DNA damage.
      reference_section_type: ABSTRACT
- term:
    id: GO:0005634
    label: nucleus
  evidence_type: IDA
  original_reference_id: PMID:11553781
  qualifier: is_active_in
  review:
    summary: Direct experimental nuclear localization; Chk1 is active in the nucleus
      where it is phosphorylated by Rad3 and inhibits Cdc25. Core localization.
    action: ACCEPT
    reason: Direct evidence consistent with Chk1's nuclear site of action.
    supported_by:
    - reference_id: PMID:11553781
      supporting_text: This checkpoint is enforced by Chk1, a protein kinase that inhibits
        the mitotic inducer Cdc25.
      reference_section_type: ABSTRACT
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IDA
  original_reference_id: PMID:11553781
  qualifier: is_active_in
  review:
    summary: A cytoplasmic pool is reported, but Chk1's documented functions are nuclear.
      Retain as non-core localization context rather than a site of established function.
    action: KEEP_AS_NON_CORE
    reason: Cytoplasmic localization observed but not the site of Chk1's characterized
      activity.
    supported_by:
    - reference_id: PMID:11553781
      supporting_text: This checkpoint is enforced by Chk1, a protein kinase that inhibits
        the mitotic inducer Cdc25.
      reference_section_type: ABSTRACT
- term:
    id: GO:0007095
    label: mitotic G2 DNA damage checkpoint signaling
  evidence_type: IMP
  original_reference_id: PMID:11553781
  qualifier: involved_in
  review:
    summary: chk1-S345A cells are checkpoint defective and DNA-damage sensitive, demonstrating
      Chk1's requirement for the G2-M DNA damage checkpoint. Core function.
    action: ACCEPT
    reason: Mutant phenotype directly demonstrates the core checkpoint role.
    supported_by:
    - reference_id: PMID:11553781
      supporting_text: The chk1-S345A cells are sensitive to DNA damage and are checkpoint
        defective.
      reference_section_type: ABSTRACT
- term:
    id: GO:0010972
    label: negative regulation of G2/M transition of mitotic cell cycle
  evidence_type: IGI
  original_reference_id: PMID:25533348
  qualifier: involved_in
  review:
    summary: Chk1 negatively regulates the G2/M transition, the molecular consequence
      of its inhibition of Cdc25 and activation of Wee1. Consistent with its checkpoint
      role.
    action: ACCEPT
    reason: Correct downstream consequence of Chk1 checkpoint signaling; supported
      by genetic interaction.
    supported_by:
    - reference_id: PMID:9278510
      supporting_text: Expression of large amounts of Chk1 produced the same phenotype
        as did loss of the cdc25 gene in cdc2-3w cells.
      reference_section_type: ABSTRACT
- term:
    id: GO:0007095
    label: mitotic G2 DNA damage checkpoint signaling
  evidence_type: IMP
  original_reference_id: PMID:9042863
  qualifier: involved_in
  review:
    summary: Establishes that the Chk1-mediated G2 DNA damage checkpoint operates through
      inhibitory Cdc2-Y15 phosphorylation (Wee1/Mik1). Core function.
    action: ACCEPT
    reason: Supports the mechanistic basis of Chk1's core G2 checkpoint function.
    supported_by:
    - reference_id: PMID:9042863
      supporting_text: the G2 DNA damage checkpoint arrest in S. pombe depends on the
        inhibitory tyrosine phosphorylation of Cdc2 carried out by the Wee1 and Mik1
        kinases.
      reference_section_type: ABSTRACT
- term:
    id: GO:0000785
    label: chromatin
  evidence_type: IDA
  original_reference_id: PMID:24006488
  qualifier: is_active_in
  review:
    summary: Chk1 associates with chromatin in the context of regulating the MBF transcription
      factor (phosphorylating Cdc10 and releasing MBF from chromatin). A genuine but
      secondary localization tied to its transcriptional-repression role.
    action: KEEP_AS_NON_CORE
    reason: Chromatin association is real but reflects the secondary MBF/transcription
      role rather than the core checkpoint signaling function.
    supported_by:
    - reference_id: PMID:24006488
      supporting_text: This modification is responsible for the repression of MBF-dependent
        transcription through induced release of MBF from chromatin.
      reference_section_type: ABSTRACT
- term:
    id: GO:0035861
    label: site of double-strand break
  evidence_type: IDA
  original_reference_id: PMID:22792081
  qualifier: is_active_in
  review:
    summary: Chk1-GFP forms foci at IR- and HO-induced DSBs that colocalize with Crb2/Rad22;
      recruitment to DSBs is where Chk1 is activated. Core localization for its checkpoint
      function.
    action: ACCEPT
    reason: Directly demonstrated DSB localization integral to Chk1 activation.
    supported_by:
    - reference_id: PMID:22792081
      supporting_text: Crb2 recruits Chk1 to double-strand breaks (DSBs) through a
        direct physical interaction.
      reference_section_type: ABSTRACT
- term:
    id: GO:0044773
    label: mitotic DNA damage checkpoint signaling
  evidence_type: IGI
  original_reference_id: PMID:12186947
  qualifier: involved_in
  review:
    summary: Chk1 is required for a checkpoint arrest in G1/early cell cycle in pre-RC
      mutant cells, broadening its checkpoint role beyond late S/G2. Consistent with
      Chk1's checkpoint signaling function.
    action: ACCEPT
    reason: Genetic evidence for Chk1 in mitotic DNA damage checkpoint signaling (G1/M
      arrest).
    supported_by:
    - reference_id: PMID:12186947
      supporting_text: The arrest depends upon the checkpoint Rad proteins and, surprisingly,
        the Chk1 protein, which is thought to act only from late S phase.
      reference_section_type: ABSTRACT
- term:
    id: GO:0000122
    label: negative regulation of transcription by RNA polymerase II
  evidence_type: IMP
  original_reference_id: PMID:24006488
  qualifier: involved_in
  review:
    summary: Upon DNA damage Chk1 phosphorylates the MBF subunit Cdc10, repressing
      MBF-dependent S-phase gene transcription. A genuine downstream effector branch
      of the DNA damage response, secondary to the core checkpoint-arrest function.
    action: KEEP_AS_NON_CORE
    reason: Real but secondary transcriptional-repression role mediated via Cdc10/MBF.
    supported_by:
    - reference_id: PMID:24006488
      supporting_text: Chk1 is activated and phosphorylates Cdc10 at its carboxy-terminal
        domain. This modification is responsible for the repression of MBF-dependent
        transcription through induced release of MBF from chromatin.
      reference_section_type: ABSTRACT
- term:
    id: GO:0004674
    label: protein serine/threonine kinase activity
  evidence_type: IDA
  original_reference_id: PMID:24006488
  qualifier: enables
  review:
    summary: Chk1 phosphorylates Cdc10 (MBF) on Ser-720/Ser-732, a direct demonstration
      of its Ser/Thr kinase activity on a physiological substrate. Core molecular
      function.
    action: ACCEPT
    reason: Direct evidence of kinase activity toward Cdc10.
    supported_by:
    - reference_id: PMID:24006488
      supporting_text: This is achieved by direct phosphorylation of Cdc10 at Ser-720
        and Ser-732 by the effector kinase Chk1.
      reference_section_type: ABSTRACT
- term:
    id: GO:0044773
    label: mitotic DNA damage checkpoint signaling
  evidence_type: IMP
  original_reference_id: PMID:24006488
  qualifier: involved_in
  review:
    summary: Chk1 activation by DNA-damaging agents and Cdc10 phosphorylation is part
      of the DNA damage checkpoint response. Consistent with Chk1's checkpoint signaling
      function.
    action: ACCEPT
    reason: Supports Chk1's role in mitotic DNA damage checkpoint signaling.
    supported_by:
    - reference_id: PMID:24006488
      supporting_text: When fission yeast cells are treated with DNA-damaging agents,
        Chk1 is activated and phosphorylates Cdc10 at its carboxy-terminal domain.
      reference_section_type: ABSTRACT
- term:
    id: GO:0005634
    label: nucleus
  evidence_type: HDA
  original_reference_id: PMID:16823372
  qualifier: is_active_in
  review:
    summary: High-throughput localization confirming nuclear presence, consistent
      with IDA data and Chk1's nuclear function.
    action: ACCEPT
    reason: Corroborates the nuclear localization of Chk1.
    supported_by:
    - reference_id: PMID:11553781
      supporting_text: This checkpoint is enforced by Chk1, a protein kinase that inhibits
        the mitotic inducer Cdc25.
      reference_section_type: ABSTRACT
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: HDA
  original_reference_id: PMID:16823372
  qualifier: is_active_in
  review:
    summary: High-throughput cytoplasmic localization. Chk1's documented functions
      are nuclear; retain as non-core context.
    action: KEEP_AS_NON_CORE
    reason: Observed cytoplasmic signal does not correspond to a site of established
      function.
    supported_by:
    - reference_id: PMID:11553781
      supporting_text: This checkpoint is enforced by Chk1, a protein kinase that inhibits
        the mitotic inducer Cdc25.
      reference_section_type: ABSTRACT
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: HDA
  original_reference_id: PMID:16823372
  qualifier: is_active_in
  review:
    summary: High-throughput cytosolic localization. As with the cytoplasm annotations,
      this is not the site of Chk1's characterized nuclear function.
    action: KEEP_AS_NON_CORE
    reason: Observed cytosolic signal does not correspond to Chk1's site of action.
    supported_by:
    - reference_id: PMID:11553781
      supporting_text: This checkpoint is enforced by Chk1, a protein kinase that inhibits
        the mitotic inducer Cdc25.
      reference_section_type: ABSTRACT
- term:
    id: GO:0005654
    label: nucleoplasm
  evidence_type: TAS
  original_reference_id: Reactome:R-SPO-75040
  qualifier: located_in
  review:
    summary: Nucleoplasmic localization (Reactome) consistent with Chk1's nuclear
      function in phosphorylating Wee1/Cdc25. Correct.
    action: ACCEPT
    reason: Consistent with nuclear localization and function.
    supported_by:
    - reference_id: PMID:11553781
      supporting_text: This checkpoint is enforced by Chk1, a protein kinase that inhibits
        the mitotic inducer Cdc25.
      reference_section_type: ABSTRACT
- term:
    id: GO:0004674
    label: protein serine/threonine kinase activity
  evidence_type: IDA
  original_reference_id: PMID:10825192
  qualifier: enables
  review:
    summary: Study of caffeine-mediated checkpoint override assays Chk1 phosphorylation/activity;
      supports Chk1 Ser/Thr kinase activity downstream of Rad3. Core molecular function.
    action: ACCEPT
    reason: Consistent with Chk1's experimentally demonstrated kinase activity.
    supported_by:
    - reference_id: PMID:10825192
      supporting_text: Caffeine prevented activation of Cds1 and phosphorylation of
        Chk1, two protein kinases that enforce the S-M checkpoint triggered by hydroxyurea.
      reference_section_type: ABSTRACT
core_functions:
- description: Effector serine/threonine protein kinase of the mitotic G2/M DNA-damage
    checkpoint; phosphorylates and inhibits the Cdc25 phosphatase and phosphorylates
    the Wee1 kinase to maintain inhibitory Cdc2/CDK1 tyrosine-15 phosphorylation and
    block mitotic entry.
  supported_by:
  - reference_id: PMID:9278510
    supporting_text: Cdc25 associated with Chk1 in vivo and was phosphorylated when
      copurified in Chk1 complexes. These findings identify Cdc25, but not Wee1, as
      a target of the DNA damage checkpoint.
    reference_section_type: ABSTRACT
  - reference_id: PMID:9034337
    supporting_text: p56chk1 can phosphorylate p107wee1 directly in vitro.
    reference_section_type: ABSTRACT
  molecular_function:
    id: GO:0004674
    label: protein serine/threonine kinase activity
  directly_involved_in:
  - id: GO:0007095
    label: mitotic G2 DNA damage checkpoint signaling
- description: DNA-damage-induced transcriptional repressor of S-phase (MBF) genes;
    phosphorylates the MBF core subunit Cdc10 to release MBF from chromatin and downregulate
    G1/S transcription.
  supported_by:
  - reference_id: PMID:24006488
    supporting_text: Chk1 is activated and phosphorylates Cdc10 at its carboxy-terminal
      domain. This modification is responsible for the repression of MBF-dependent
      transcription through induced release of MBF from chromatin.
    reference_section_type: ABSTRACT
  molecular_function:
    id: GO:0004674
    label: protein serine/threonine kinase activity
  directly_involved_in:
  - id: GO:0000122
    label: negative regulation of transcription by RNA polymerase II
proposed_new_terms: []
suggested_questions:
- question: What is the complete set of physiological Chk1 substrates beyond Cdc25,
    Wee1, and Cdc10 in fission yeast, and how does substrate selection change between
    the mitotic, G1, and meiotic checkpoints?
- question: How is Chk1 activity terminated during checkpoint recovery/adaptation,
    and which phosphatases reverse Rad3-dependent Chk1 phosphorylation?
suggested_experiments:
- description: Quantitative phosphoproteomics of synchronized chk1+ versus chk1Δ (and
    chk1-S345A) cells before and after defined DNA damage to map the in vivo Chk1-dependent
    phosphorylation network.
- description: Analog-sensitive Chk1 (chk1-as) combined with rapid kinase inhibition
    and live imaging to define the kinetics of Cdc25/Wee1/Cdc10 phosphorylation and
    checkpoint maintenance versus recovery.