id: Q9ULC4
gene_symbol: MCTS1
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: MCTS1 (Malignant T-cell-amplified sequence 1, MCT-1) is a cytoplasmic PUA-domain RNA-binding protein that, together with its obligate partner DENR, forms the MCTS1-DENR heterodimer, a non-canonical translation factor equivalent to eIF2D (Ligatin) split into two polypeptides (MCTS1 corresponds to the N-terminal half and DENR to the C-terminal SUI1 half). MCTS1 contributes the PUA domain that engages mRNA/the cap region and binds the 40S small ribosomal subunit, and recruits DENR. The complex acts at the post-termination 40S ribosome to promote translation reinitiation, particularly after short upstream ORFs (uORFs), and to recycle/recover post-termination 40S subunits by promoting release of deacylated tRNA and mRNA after ABCE1-mediated ribosome splitting; it also delivers initiator tRNA to the 40S P-site in an eIF2-independent manner when the start codon is positioned in the P-site (as on HCV-like IRESs). MCTS1-DENR-dependent reinitiation governs translation of a specific set of mRNAs (including JAK2) and is required for IFN-gamma immunity. MCTS1 was originally identified as an oncogene amplified in T-cell lymphoma.
existing_annotations:
- term:
    id: GO:0001731
    label: formation of translation preinitiation complex
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: Phylogenetic transfer of preinitiation-complex formation, consistent with the MCTS1-DENR complex assembling tRNA onto 40S/mRNA complexes for (re)initiation.
    action: ACCEPT
    reason: Corroborated by direct experimental evidence that MCT-1/DENR promotes recruitment of initiator tRNA to 40S/mRNA complexes.
    supported_by:
    - reference_id: PMID:20713520
      supporting_text: promote efficient eIF2-independent recruitment of Met-tRNA(Met)(i) to 40S/mRNA complexes
- term:
    id: GO:0002188
    label: translation reinitiation
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  qualifier: involved_in
  review:
    summary: Automated assignment of translation reinitiation, the central biological process of the MCTS1-DENR complex.
    action: ACCEPT
    reason: Strongly supported by direct experimental and IMP/IDA evidence for the MCTS1-DENR complex; this is core to MCTS1 function.
    supported_by:
    - reference_id: PMID:29889857
      supporting_text: DENR-MCTS1 heterodimerization and tRNA recruitment are required for translation reinitiation
- term:
    id: GO:0003723
    label: RNA binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: InterPro PUA-domain-based assignment of RNA binding. MCTS1 has a PUA domain and engages mRNA/cap region; RNA binding is a reasonable parent molecular function.
    action: KEEP_AS_NON_CORE
    reason: Correct but generic; the specific informative activities are 40S binding, cap-complex/PUA-mediated mRNA engagement and reinitiation-factor activity.
    supported_by:
    - reference_id: PMID:16982740
      supporting_text: MCT-1 contains the PUA domain, a recently described RNA-binding domain
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: Automated cytoplasmic localization, consistent with experimental evidence.
    action: ACCEPT
    reason: Agrees with EXP/IDA cytoplasm evidence; MCTS1 acts on cytoplasmic ribosomes.
    supported_by:
    - reference_id: file:human/MCTS1/MCTS1-goa.tsv
      supporting_text: GO:0005737 cytoplasm cellular_component ECO:0000269 EXP PMID:11709712
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:16169070
  qualifier: enables
  review:
    summary: IntAct interaction with DENR (O43583), MCTS1's obligate functional partner.
    action: KEEP_AS_NON_CORE
    reason: Records the functionally central DENR interaction; bare protein binding is not elevated to core but the heterodimer is captured in core_functions.
    supported_by:
    - reference_id: file:human/MCTS1/MCTS1-goa.tsv
      supporting_text: GO:0005515 protein binding molecular_function ECO:0000353 IPI PMID:16169070 UniProtKB:O43583
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:21516116
  qualifier: enables
  review:
    summary: IntAct interaction with DENR (O43583), the obligate MCTS1 partner.
    action: KEEP_AS_NON_CORE
    reason: Records the functionally central DENR interaction; bare protein binding is not elevated to core but the heterodimer is captured in core_functions.
    supported_by:
    - reference_id: file:human/MCTS1/MCTS1-goa.tsv
      supporting_text: GO:0005515 protein binding molecular_function ECO:0000353 IPI PMID:21516116 UniProtKB:O43583
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:32296183
  qualifier: enables
  review:
    summary: IntAct interaction with DENR (O43583), the obligate MCTS1 partner.
    action: KEEP_AS_NON_CORE
    reason: Records the functionally central DENR interaction; bare protein binding is not elevated to core but the heterodimer is captured in core_functions.
    supported_by:
    - reference_id: file:human/MCTS1/MCTS1-goa.tsv
      supporting_text: GO:0005515 protein binding molecular_function ECO:0000353 IPI PMID:32296183 UniProtKB:O43583
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:33961781
  qualifier: enables
  review:
    summary: BioPlex interaction with DENR (O43583), the obligate MCTS1 partner.
    action: KEEP_AS_NON_CORE
    reason: Records the functionally central DENR interaction; bare protein binding is not elevated to core but the heterodimer is captured in core_functions.
    supported_by:
    - reference_id: file:human/MCTS1/MCTS1-goa.tsv
      supporting_text: GO:0005515 protein binding molecular_function ECO:0000353 IPI PMID:33961781 UniProtKB:O43583
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:40205054
  qualifier: enables
  review:
    summary: Cell-maps interactome interaction with DENR (O43583), the obligate MCTS1 partner.
    action: KEEP_AS_NON_CORE
    reason: Records the functionally central DENR interaction; bare protein binding is not elevated to core but the heterodimer is captured in core_functions.
    supported_by:
    - reference_id: file:human/MCTS1/MCTS1-goa.tsv
      supporting_text: GO:0005515 protein binding molecular_function ECO:0000353 IPI PMID:40205054 UniProtKB:O43583
- term:
    id: GO:0002188
    label: translation reinitiation
  evidence_type: IDA
  original_reference_id: PMID:37875108
  qualifier: involved_in
  review:
    summary: Direct evidence (ComplexPortal/IDA) that the MCTS1-DENR complex mediates translation reinitiation, shown for JAK2 and other targets.
    action: ACCEPT
    reason: Direct experimental support for the core reinitiation function of MCTS1.
    supported_by:
    - reference_id: PMID:37875108
      supporting_text: Human MCTS1-dependent translation of JAK2 is essential for IFN-γ immunity to mycobacteria.
- term:
    id: GO:0070992
    label: translation initiation complex
  evidence_type: IPI
  original_reference_id: PMID:29889857
  qualifier: part_of
  review:
    summary: MCTS1 is part of the MCTS1-DENR (re)initiation complex; heterodimerization with DENR and tRNA recruitment are required for reinitiation.
    action: ACCEPT
    reason: Supported by structural/biochemical demonstration that MCTS1-DENR heterodimerize to form the functional reinitiation complex.
    supported_by:
    - reference_id: PMID:29889857
      supporting_text: DENR-MCTS1 heterodimerization and tRNA recruitment are required for translation reinitiation
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: IDA
  original_reference_id: GO_REF:0000052
  qualifier: located_in
  review:
    summary: Direct immunofluorescence (HPA) cytosolic localization, consistent with the cytoplasmic site of action.
    action: ACCEPT
    reason: IDA-supported cytosolic localization agrees with MCTS1's role on cytoplasmic ribosomes.
    supported_by:
    - reference_id: file:human/MCTS1/MCTS1-goa.tsv
      supporting_text: GO:0005829 cytosol cellular_component ECO:0000314 IDA GO_REF:0000052
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: EXP
  original_reference_id: PMID:11709712
  qualifier: located_in
  review:
    summary: Experimental cytoplasmic localization from the original MCT-1 oncogene characterization.
    action: ACCEPT
    reason: Experimentally supported cytoplasmic localization consistent with MCTS1's site of action.
    supported_by:
    - reference_id: file:human/MCTS1/MCTS1-goa.tsv
      supporting_text: GO:0005737 cytoplasm cellular_component ECO:0000269 EXP PMID:11709712
- term:
    id: GO:0003743
    label: translation initiation factor activity
  evidence_type: IDA
  original_reference_id: PMID:20713520
  qualifier: enables
  review:
    summary: Direct evidence that MCT-1/DENR functions as a non-canonical (eIF2D-like) factor that delivers initiator tRNA to the 40S P-site; this is a core molecular function.
    action: ACCEPT
    reason: Experimentally established (re)initiation-factor activity of the MCTS1-DENR complex; MCTS1 is an essential subunit.
    supported_by:
    - reference_id: PMID:20713520
      supporting_text: promote efficient eIF2-independent recruitment of Met-tRNA(Met)(i) to 40S/mRNA complexes
- term:
    id: GO:0000339
    label: RNA cap binding
  evidence_type: IDA
  original_reference_id: PMID:16982740
  qualifier: enables
  review:
    summary: MCT-1 interacts with the cap complex through its PUA domain. This was interpreted as cap-complex association; whether MCTS1 directly binds the m7G cap or associates via the cap-binding complex is less certain, but the PUA-mediated engagement at the cap is documented.
    action: KEEP_AS_NON_CORE
    reason: Supported by direct evidence of cap-complex interaction via the PUA domain, but the primary informative function is reinitiation/40S recycling; retained as non-core.
    supported_by:
    - reference_id: PMID:16982740
      supporting_text: MCT-1 protein interacts with the cap complex through its PUA domain
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:16982740
  qualifier: enables
  review:
    summary: UniProt-curated interaction with DENR (O43583); the foundational report that MCT-1 recruits DENR/DRP via the PUA/SUI1 interface.
    action: KEEP_AS_NON_CORE
    reason: Records the functionally central DENR interaction; bare protein binding is not elevated to core but the heterodimer is captured in core_functions.
    supported_by:
    - reference_id: PMID:16982740
      supporting_text: recruits the density-regulated protein (DENR/DRP), containing the SUI1 translation initiation domain
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IDA
  original_reference_id: PMID:16982740
  qualifier: is_active_in
  review:
    summary: Direct evidence that MCTS1 is active in the cytoplasm where it associates with the cap complex and 40S ribosomes.
    action: ACCEPT
    reason: IDA-supported cytoplasmic site of action.
    supported_by:
    - reference_id: file:human/MCTS1/MCTS1-goa.tsv
      supporting_text: GO:0005737 cytoplasm cellular_component ECO:0000314 IDA PMID:16982740
- term:
    id: GO:0043024
    label: ribosomal small subunit binding
  evidence_type: IDA
  original_reference_id: PMID:20713520
  qualifier: enables
  review:
    summary: MCT-1/DENR binds 40S small ribosomal subunits to deliver tRNA and to promote recycling; direct binding to the 40S subunit is a core molecular function.
    action: ACCEPT
    reason: Direct experimental evidence of MCTS1-DENR action on 40S subunits; binding the small subunit underlies its reinitiation/recycling activities.
    supported_by:
    - reference_id: PMID:20713520
      supporting_text: promote efficient eIF2-independent recruitment of Met-tRNA(Met)(i) to 40S/mRNA complexes
- term:
    id: GO:0002188
    label: translation reinitiation
  evidence_type: IMP
  original_reference_id: PMID:37875108
  qualifier: involved_in
  review:
    summary: Loss-of-function (patient) evidence that MCTS1 is required for translation reinitiation of specific mRNAs (e.g. JAK2). The JAK2 5'UTR carries three uORFs (two ultra-short start-stop uORFs); without MCTS1, post-uORF 40S ribosomes stall because deacylated tRNA is not removed, blocking reinitiation on the main JAK2 ORF.
    action: ACCEPT
    reason: IMP evidence directly supports the core reinitiation function of MCTS1, with the JAK2 5'UTR uORF architecture providing the mechanistic basis for its dependence on MCTS1-DENR reinitiation.
    supported_by:
    - reference_id: PMID:37875108
      supporting_text: Human MCTS1-dependent translation of JAK2 is essential for IFN-γ immunity to mycobacteria.
    - reference_id: PMID:37875108
      supporting_text: We identified three uORFs within the JAK2
    - reference_id: PMID:37875108
      supporting_text: In the absence of MCTS1 or DENR, 40S ribosomes stall on the uORF stop codon, because the deacylated tRNA cannot be removed
- term:
    id: GO:0032790
    label: ribosome disassembly
  evidence_type: IMP
  original_reference_id: PMID:37875108
  qualifier: involved_in
  review:
    summary: Loss-of-function evidence linking MCTS1 to the 40S recycling/disassembly step that underpins reinitiation. The Bohlen 2023 full text directly assays MCTS1KO and patient cells, showing accumulation of stalled post-termination 40S subunits and 80S queueing when MCTS1 is absent, establishing impaired ribosome recycling as an MCTS1-specific defect.
    action: ACCEPT
    reason: Consistent with the established role of MCTS1-DENR in clearing post-termination 40S subunits; supported by both IMP (MCTS1KO/patient-cell recycling defects) and the biochemical recycling assays.
    supported_by:
    - reference_id: PMID:20713520
      supporting_text: Ligatin and MCT-1/DENR can promote release of deacylated tRNA and mRNA from recycled 40S subunits after ABCE1-mediated dissociation of post-termination ribosomes
    - reference_id: PMID:37875108
      supporting_text: the DENR-MCTS1 complex removes the tRNA from the 40S ribosome on the stop codon, as a part of ribosome recycling
    - reference_id: PMID:37875108
      supporting_text: MCTS1KO HeLa cells, thus, have impaired ribosome recycling
    - reference_id: file:human/MCTS1/MCTS1-deep-research-falcon.md
      supporting_text: loss of MCTS1 causes stalled post-termination 40S ribosomes at stop codons and 80S ribosome queueing upstream, demonstrating a role in ribosome recycling in addition to re-initiation
- term:
    id: GO:0075522
    label: IRES-dependent viral translational initiation
  evidence_type: IDA
  original_reference_id: PMID:20713520
  qualifier: involved_in
  review:
    summary: MCT-1/DENR promotes eIF2-independent recruitment of initiator tRNA on HCV-like IRESs and SV 26S mRNA, where the start codon is placed directly in the P-site.
    action: KEEP_AS_NON_CORE
    reason: A genuine but specialized application of MCTS1-DENR's P-site tRNA delivery activity (viral IRES context); non-core relative to cellular reinitiation.
    supported_by:
    - reference_id: PMID:20713520
      supporting_text: promote efficient eIF2-independent recruitment of Met-tRNA(Met)(i) to 40S/mRNA complexes, if attachment of 40S subunits to the mRNA places the initiation codon directly in the P site, as on HCV-like IRESs
- term:
    id: GO:0001731
    label: formation of translation preinitiation complex
  evidence_type: IDA
  original_reference_id: PMID:20713520
  qualifier: involved_in
  review:
    summary: Direct evidence that MCT-1/DENR assembles initiator tRNA onto 40S/mRNA complexes for reinitiation/recycling.
    action: ACCEPT
    reason: Direct experimental support for MCTS1's role in assembling the tRNA-loaded 40S complex.
    supported_by:
    - reference_id: PMID:20713520
      supporting_text: promote efficient eIF2-independent recruitment of Met-tRNA(Met)(i) to 40S/mRNA complexes
- term:
    id: GO:0032790
    label: ribosome disassembly
  evidence_type: IDA
  original_reference_id: PMID:20713520
  qualifier: involved_in
  review:
    summary: MCT-1/DENR promotes release of deacylated tRNA and mRNA from recycled 40S subunits after ABCE1-mediated splitting of post-termination ribosomes.
    action: ACCEPT
    reason: Direct experimental support for MCTS1's role in 40S recycling/recovery.
    supported_by:
    - reference_id: PMID:20713520
      supporting_text: Ligatin and MCT-1/DENR can promote release of deacylated tRNA and mRNA from recycled 40S subunits after ABCE1-mediated dissociation of post-termination ribosomes
references:
- 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
  findings: []
- id: GO_REF:0000052
  title: Gene Ontology annotation based on curation of immunofluorescence data
  findings: []
- id: GO_REF:0000117
  title: Electronic Gene Ontology annotations created by ARBA machine learning models
  findings: []
- id: PMID:11709712
  title: Expression and stabilization of the MCT-1 protein by DNA damaging agents.
  findings:
  - statement: MCT-1 (MCTS1) protein is expressed in the cytoplasm and is stabilized by DNA-damaging agents.
    reference_section_type: RESULTS
- id: PMID:16169070
  title: 'A human protein-protein interaction network: a resource for annotating the proteome.'
  findings: []
- id: PMID:16982740
  title: MCT-1 protein interacts with the cap complex and modulates messenger RNA translational profiles.
  findings:
  - statement: MCT-1 interacts with the cap complex through its PUA domain and recruits DENR/DRP, which contains the SUI1 translation initiation domain.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Cached publication title matches the YAML title; biochemical study establishing MCTS1 cap-complex association and DENR/SUI1 recruitment, supporting its translation-reinitiation role.
- id: PMID:20713520
  title: Activities of Ligatin and MCT-1/DENR in eukaryotic translation initiation and ribosomal recycling.
  findings:
  - statement: MCT-1 and DENR together promote eIF2-independent recruitment of initiator tRNA to 40S/mRNA complexes when the initiation codon is in the P-site, and promote release of deacylated tRNA and mRNA from recycled 40S subunits after ABCE1-mediated ribosome dissociation.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Cached publication title matches the YAML title; reconstitution study establishing the MCTS1/DENR (Ligatin-like) role in eIF2-independent initiator-tRNA recruitment and 40S ribosomal recycling, the gene's core molecular function.
- id: PMID:21516116
  title: Next-generation sequencing to generate interactome datasets.
  findings: []
- id: PMID:29889857
  title: DENR-MCTS1 heterodimerization and tRNA recruitment are required for translation reinitiation.
  findings:
  - statement: MCTS1 and DENR heterodimerize and this, together with tRNA recruitment, is required for translation reinitiation.
    reference_section_type: TITLE
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Cached publication title matches the YAML title; demonstrates that MCTS1-DENR heterodimerization and tRNA recruitment are required for translation reinitiation, directly supporting the core function.
- id: PMID:32296183
  title: A reference map of the human binary protein interactome.
  findings: []
- id: PMID:33961781
  title: Dual proteome-scale networks reveal cell-specific remodeling of the human interactome.
  findings: []
- id: PMID:37875108
  title: Human MCTS1-dependent translation of JAK2 is essential for IFN-γ immunity to mycobacteria.
  findings:
  - statement: MCTS1-DENR-dependent translation reinitiation is required for translation of JAK2 and for IFN-gamma immunity to mycobacteria.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Cached publication title matches the YAML title; provides the in vivo physiological significance of MCTS1-DENR reinitiation (JAK2 translation, IFN-gamma immunity).
- id: PMID:40205054
  title: Multimodal cell maps as a foundation for structural and functional genomics.
  findings: []
- id: file:human/MCTS1/MCTS1-deep-research-falcon.md
  title: Falcon deep research report for MCTS1
  findings:
  - statement: MCTS1 forms a heterodimer with DENR and acts on post-termination 40S ribosomal subunits to promote re-initiation after uORFs and to recycle ribosomes; loss of MCTS1 causes stalled post-termination 40S ribosomes and 80S queueing. MCTS1-dependent reinitiation is required for translation of a selective set (~200-240) of uORF-containing mRNAs, most notably JAK2, with physiological relevance to IFN-gamma immunity.
    reference_section_type: OTHER
  reference_review:
    relevance: HIGH
    correctness: UNVERIFIED
    review_notes: 'LLM-synthesized (Edison/Falcon) summary, marked UNVERIFIED pending source-by-source checking. The core MCTS1-specific claims it makes (cytoplasmic, 40S-/ribosome-associated non-canonical reinitiation+recycling factor obligately partnered with DENR; JAK2 5''UTR uORF dependence; impaired recycling on MCTS1 loss) are independently corroborated by the cached full text of Bohlen 2023 (PMID:37875108) and by the existing experimental annotations, so they are reliable. CAVEATS: (1) much of the mechanistic and target-class detail (uORF re-initiation, ATF4, mitotic translation, ~200-240 targets) derives from DENR-centric or MCTS1-DENR-complex work (Castelo-Szekely 2019, Meurs 2024/2025, von Hohenberg 2022, Vasudevan 2020) and should be read as properties of the heterodimer, not of MCTS1 in isolation. (2) The oncogene/cancer claims (PA2G4-P48 stabilization in HNSCC, IL-6/IL-6R/STAT3, EMT/stemness; Sun 2023, Weng 2019) are phenotypic/association-level and do not by themselves establish a distinct MCTS1 molecular function beyond translational control; not used to add or strengthen molecular-function annotations here. None of these cited papers (except PMID:37875108) are in the local publications cache, so their supporting_text was not independently verified.'
core_functions:
- description: As an essential subunit of the MCTS1-DENR heterodimer (an eIF2D-like non-canonical factor), binds the 40S small ribosomal subunit and (via its PUA domain) mRNA/the cap region, recruits DENR, and delivers initiator tRNA to the 40S P-site in an eIF2-independent manner to drive translation reinitiation after short uORFs.
  molecular_function:
    id: GO:0003743
    label: translation initiation factor activity
  locations:
  - id: GO:0005737
    label: cytoplasm
  supported_by:
  - reference_id: PMID:20713520
    supporting_text: promote efficient eIF2-independent recruitment of Met-tRNA(Met)(i) to 40S/mRNA complexes
  - reference_id: PMID:29889857
    supporting_text: DENR-MCTS1 heterodimerization and tRNA recruitment are required for translation reinitiation
- description: Binds the 40S small ribosomal subunit, the structural basis for the MCTS1-DENR complex's action in delivering tRNA and recycling post-termination 40S subunits.
  molecular_function:
    id: GO:0043024
    label: ribosomal small subunit binding
  locations:
  - id: GO:0005737
    label: cytoplasm
  supported_by:
  - reference_id: file:human/MCTS1/MCTS1-goa.tsv
    supporting_text: GO:0043024 ribosomal small subunit binding molecular_function ECO:0000314 IDA PMID:20713520
proposed_new_terms: []
suggested_questions:
- question: Does MCTS1 directly bind the m7G cap, or is its association with the cap complex indirect (via eIF4 components), and how does the PUA domain contribute?
- question: Which features of target mRNAs (uORF architecture, 5' UTR structure) determine MCTS1-DENR dependence, and how does this relate to MCTS1's oncogenic activity?
suggested_experiments:
- description: Cross-linking/CLIP of MCTS1 to define its direct RNA-binding sites genome-wide and test whether it contacts the cap-proximal region directly.
- description: Reconstituted 40S P-site tRNA delivery and recycling assays with purified MCTS1, DENR and ABCE1 to dissect MCTS1's specific contribution to each step.