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.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0001731
formation of translation preinitiation complex
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: Phylogenetic transfer of preinitiation-complex formation, consistent with the MCTS1-DENR complex assembling tRNA onto 40S/mRNA complexes for (re)initiation.
Reason: Corroborated by direct experimental evidence that MCT-1/DENR promotes recruitment of initiator tRNA to 40S/mRNA complexes.
Supporting Evidence:
PMID:20713520
promote efficient eIF2-independent recruitment of Met-tRNA(Met)(i) to 40S/mRNA complexes
|
|
GO:0002188
translation reinitiation
|
IEA
GO_REF:0000117 |
ACCEPT |
Summary: Automated assignment of translation reinitiation, the central biological process of the MCTS1-DENR complex.
Reason: Strongly supported by direct experimental and IMP/IDA evidence for the MCTS1-DENR complex; this is core to MCTS1 function.
Supporting Evidence:
PMID:29889857
DENR-MCTS1 heterodimerization and tRNA recruitment are required for translation reinitiation
|
|
GO:0003723
RNA binding
|
IEA
GO_REF:0000002 |
KEEP AS NON CORE |
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.
Reason: Correct but generic; the specific informative activities are 40S binding, cap-complex/PUA-mediated mRNA engagement and reinitiation-factor activity.
Supporting Evidence:
PMID:16982740
MCT-1 contains the PUA domain, a recently described RNA-binding domain
|
|
GO:0005737
cytoplasm
|
IEA
GO_REF:0000044 |
ACCEPT |
Summary: Automated cytoplasmic localization, consistent with experimental evidence.
Reason: Agrees with EXP/IDA cytoplasm evidence; MCTS1 acts on cytoplasmic ribosomes.
Supporting Evidence:
file:human/MCTS1/MCTS1-goa.tsv
GO:0005737 cytoplasm cellular_component ECO:0000269 EXP PMID:11709712
|
|
GO:0005515
protein binding
|
IPI
PMID:16169070 A human protein-protein interaction network: a resource for ... |
KEEP AS NON CORE |
Summary: IntAct interaction with DENR (O43583), MCTS1's obligate functional partner.
Reason: Records the functionally central DENR interaction; bare protein binding is not elevated to core but the heterodimer is captured in core_functions.
Supporting Evidence:
file:human/MCTS1/MCTS1-goa.tsv
GO:0005515 protein binding molecular_function ECO:0000353 IPI PMID:16169070 UniProtKB:O43583
|
|
GO:0005515
protein binding
|
IPI
PMID:21516116 Next-generation sequencing to generate interactome datasets. |
KEEP AS NON CORE |
Summary: IntAct interaction with DENR (O43583), the obligate MCTS1 partner.
Reason: Records the functionally central DENR interaction; bare protein binding is not elevated to core but the heterodimer is captured in core_functions.
Supporting Evidence:
file:human/MCTS1/MCTS1-goa.tsv
GO:0005515 protein binding molecular_function ECO:0000353 IPI PMID:21516116 UniProtKB:O43583
|
|
GO:0005515
protein binding
|
IPI
PMID:32296183 A reference map of the human binary protein interactome. |
KEEP AS NON CORE |
Summary: IntAct interaction with DENR (O43583), the obligate MCTS1 partner.
Reason: Records the functionally central DENR interaction; bare protein binding is not elevated to core but the heterodimer is captured in core_functions.
Supporting Evidence:
file:human/MCTS1/MCTS1-goa.tsv
GO:0005515 protein binding molecular_function ECO:0000353 IPI PMID:32296183 UniProtKB:O43583
|
|
GO:0005515
protein binding
|
IPI
PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling... |
KEEP AS NON CORE |
Summary: BioPlex interaction with DENR (O43583), the obligate MCTS1 partner.
Reason: Records the functionally central DENR interaction; bare protein binding is not elevated to core but the heterodimer is captured in core_functions.
Supporting Evidence:
file:human/MCTS1/MCTS1-goa.tsv
GO:0005515 protein binding molecular_function ECO:0000353 IPI PMID:33961781 UniProtKB:O43583
|
|
GO:0005515
protein binding
|
IPI
PMID:40205054 Multimodal cell maps as a foundation for structural and func... |
KEEP AS NON CORE |
Summary: Cell-maps interactome interaction with DENR (O43583), the obligate MCTS1 partner.
Reason: Records the functionally central DENR interaction; bare protein binding is not elevated to core but the heterodimer is captured in core_functions.
Supporting Evidence:
file:human/MCTS1/MCTS1-goa.tsv
GO:0005515 protein binding molecular_function ECO:0000353 IPI PMID:40205054 UniProtKB:O43583
|
|
GO:0002188
translation reinitiation
|
IDA
PMID:37875108 Human MCTS1-dependent translation of JAK2 is essential for I... |
ACCEPT |
Summary: Direct evidence (ComplexPortal/IDA) that the MCTS1-DENR complex mediates translation reinitiation, shown for JAK2 and other targets.
Reason: Direct experimental support for the core reinitiation function of MCTS1.
Supporting Evidence:
PMID:37875108
Human MCTS1-dependent translation of JAK2 is essential for IFN-γ immunity to mycobacteria.
|
|
GO:0070992
translation initiation complex
|
IPI
PMID:29889857 DENR-MCTS1 heterodimerization and tRNA recruitment are requi... |
ACCEPT |
Summary: MCTS1 is part of the MCTS1-DENR (re)initiation complex; heterodimerization with DENR and tRNA recruitment are required for reinitiation.
Reason: Supported by structural/biochemical demonstration that MCTS1-DENR heterodimerize to form the functional reinitiation complex.
Supporting Evidence:
PMID:29889857
DENR-MCTS1 heterodimerization and tRNA recruitment are required for translation reinitiation
|
|
GO:0005829
cytosol
|
IDA
GO_REF:0000052 |
ACCEPT |
Summary: Direct immunofluorescence (HPA) cytosolic localization, consistent with the cytoplasmic site of action.
Reason: IDA-supported cytosolic localization agrees with MCTS1's role on cytoplasmic ribosomes.
Supporting Evidence:
file:human/MCTS1/MCTS1-goa.tsv
GO:0005829 cytosol cellular_component ECO:0000314 IDA GO_REF:0000052
|
|
GO:0005737
cytoplasm
|
EXP
PMID:11709712 Expression and stabilization of the MCT-1 protein by DNA dam... |
ACCEPT |
Summary: Experimental cytoplasmic localization from the original MCT-1 oncogene characterization.
Reason: Experimentally supported cytoplasmic localization consistent with MCTS1's site of action.
Supporting Evidence:
file:human/MCTS1/MCTS1-goa.tsv
GO:0005737 cytoplasm cellular_component ECO:0000269 EXP PMID:11709712
|
|
GO:0003743
translation initiation factor activity
|
IDA
PMID:20713520 Activities of Ligatin and MCT-1/DENR in eukaryotic translati... |
ACCEPT |
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.
Reason: Experimentally established (re)initiation-factor activity of the MCTS1-DENR complex; MCTS1 is an essential subunit.
Supporting Evidence:
PMID:20713520
promote efficient eIF2-independent recruitment of Met-tRNA(Met)(i) to 40S/mRNA complexes
|
|
GO:0000339
RNA cap binding
|
IDA
PMID:16982740 MCT-1 protein interacts with the cap complex and modulates m... |
KEEP AS NON CORE |
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.
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.
Supporting Evidence:
PMID:16982740
MCT-1 protein interacts with the cap complex through its PUA domain
|
|
GO:0005515
protein binding
|
IPI
PMID:16982740 MCT-1 protein interacts with the cap complex and modulates m... |
KEEP AS NON CORE |
Summary: UniProt-curated interaction with DENR (O43583); the foundational report that MCT-1 recruits DENR/DRP via the PUA/SUI1 interface.
Reason: Records the functionally central DENR interaction; bare protein binding is not elevated to core but the heterodimer is captured in core_functions.
Supporting Evidence:
PMID:16982740
recruits the density-regulated protein (DENR/DRP), containing the SUI1 translation initiation domain
|
|
GO:0005737
cytoplasm
|
IDA
PMID:16982740 MCT-1 protein interacts with the cap complex and modulates m... |
ACCEPT |
Summary: Direct evidence that MCTS1 is active in the cytoplasm where it associates with the cap complex and 40S ribosomes.
Reason: IDA-supported cytoplasmic site of action.
Supporting Evidence:
file:human/MCTS1/MCTS1-goa.tsv
GO:0005737 cytoplasm cellular_component ECO:0000314 IDA PMID:16982740
|
|
GO:0043024
ribosomal small subunit binding
|
IDA
PMID:20713520 Activities of Ligatin and MCT-1/DENR in eukaryotic translati... |
ACCEPT |
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.
Reason: Direct experimental evidence of MCTS1-DENR action on 40S subunits; binding the small subunit underlies its reinitiation/recycling activities.
Supporting Evidence:
PMID:20713520
promote efficient eIF2-independent recruitment of Met-tRNA(Met)(i) to 40S/mRNA complexes
|
|
GO:0002188
translation reinitiation
|
IMP
PMID:37875108 Human MCTS1-dependent translation of JAK2 is essential for I... |
ACCEPT |
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.
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.
Supporting Evidence:
PMID:37875108
Human MCTS1-dependent translation of JAK2 is essential for IFN-γ immunity to mycobacteria.
PMID:37875108
We identified three uORFs within the JAK2
PMID:37875108
In the absence of MCTS1 or DENR, 40S ribosomes stall on the uORF stop codon, because the deacylated tRNA cannot be removed
|
|
GO:0032790
ribosome disassembly
|
IMP
PMID:37875108 Human MCTS1-dependent translation of JAK2 is essential for I... |
ACCEPT |
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.
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.
Supporting Evidence:
PMID:20713520
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
PMID:37875108
the DENR-MCTS1 complex removes the tRNA from the 40S ribosome on the stop codon, as a part of ribosome recycling
PMID:37875108
MCTS1KO HeLa cells, thus, have impaired ribosome recycling
file:human/MCTS1/MCTS1-deep-research-falcon.md
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
|
|
GO:0075522
IRES-dependent viral translational initiation
|
IDA
PMID:20713520 Activities of Ligatin and MCT-1/DENR in eukaryotic translati... |
KEEP AS NON CORE |
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.
Reason: A genuine but specialized application of MCTS1-DENR's P-site tRNA delivery activity (viral IRES context); non-core relative to cellular reinitiation.
Supporting Evidence:
PMID:20713520
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
|
|
GO:0001731
formation of translation preinitiation complex
|
IDA
PMID:20713520 Activities of Ligatin and MCT-1/DENR in eukaryotic translati... |
ACCEPT |
Summary: Direct evidence that MCT-1/DENR assembles initiator tRNA onto 40S/mRNA complexes for reinitiation/recycling.
Reason: Direct experimental support for MCTS1's role in assembling the tRNA-loaded 40S complex.
Supporting Evidence:
PMID:20713520
promote efficient eIF2-independent recruitment of Met-tRNA(Met)(i) to 40S/mRNA complexes
|
|
GO:0032790
ribosome disassembly
|
IDA
PMID:20713520 Activities of Ligatin and MCT-1/DENR in eukaryotic translati... |
ACCEPT |
Summary: MCT-1/DENR promotes release of deacylated tRNA and mRNA from recycled 40S subunits after ABCE1-mediated splitting of post-termination ribosomes.
Reason: Direct experimental support for MCTS1's role in 40S recycling/recovery.
Supporting Evidence:
PMID:20713520
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
|
Q: 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?
Q: Which features of target mRNAs (uORF architecture, 5' UTR structure) determine MCTS1-DENR dependence, and how does this relate to MCTS1's oncogenic activity?
Experiment: Cross-linking/CLIP of MCTS1 to define its direct RNA-binding sites genome-wide and test whether it contacts the cap-proximal region directly.
Experiment: Reconstituted 40S P-site tRNA delivery and recycling assays with purified MCTS1, DENR and ABCE1 to dissect MCTS1's specific contribution to each step.
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Malignant T-cell-amplified sequence 1 (MCTS1, also known as MCT-1) is a non-canonical translation factor in humans, primarily functioning as a translation re-initiation and ribosome recycling factor through its heterodimeric partnership with DENR. This essential regulatory protein is cytoplasmic and universally expressed, exerting control over selective mRNA translation—most notably JAK2, a key kinase in immune signaling. MCTS1 is critical for immunity, adaptive cellular stress responses, mitotic progression, and has emerging roles in cancer biology.
| Molecular Function | Mechanism of Action | Substrate/Targets | Subcellular Localization | Key Pathways |
|---|---|---|---|---|
| Non-canonical translation re-initiation factor | MCTS1 forms a heterodimer with DENR and acts on post-termination 40S ribosomal subunits to promote re-initiation after translation of upstream open reading frames (uORFs); proposed activities include removal of deacylated P-site tRNA and/or delivery of a new initiator tRNA, thereby restoring scanning competence for downstream CDS translation (meurs2024aninvitro pages 1-4, meurs2025mcts2anddistinct pages 1-2, meurs2025mcts2anddistinct pages 2-3) | uORF-containing transcripts as a selective class; DENR-responsive transcripts are enriched for translated uORFs, including both 1-aa/start-stop and longer uORFs (meurs2024aninvitro pages 4-7, meurs2025mcts2anddistinct pages 2-3) | Cytoplasmic, ribosome-associated; binds the small ribosomal subunit/40S and functions on translating ribosomes during re-initiation and ribosome recycling (casteloszekely2019chartingdenrdependenttranslation pages 1-2, hohenberg2022cyclinbcdk1and pages 1-2, weng2019mct1mir34ail6il6rsignalingaxis pages 1-2) | Core translational control pathway governing uORF-dependent re-initiation and selective protein synthesis (meurs2024aninvitro pages 1-4, sriram2018translationacrobaticshow pages 1-2) |
| Ribosome recycling factor in the DENR-MCTS1 complex | After ORF termination, the DENR-MCTS1 complex removes tRNA from 40S ribosomes; 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 (bohlen2023humanmcts1dependenttranslation pages 5-6, bohlen2023humanmcts1dependenttranslation pages 6-8) | Post-termination 40S ribosomes on main ORFs and uORFs; stop-codon contexts with certain penultimate codons show stronger dependence (bohlen2023humanmcts1dependenttranslation pages 5-6, bohlen2023humanmcts1dependenttranslation pages 6-8, meurs2025mcts2anddistinct pages 2-3) | Cytoplasmic, on mRNA-bound ribosomes during translation termination/recycling (bohlen2023humanmcts1dependenttranslation pages 5-6, bohlen2023humanmcts1dependenttranslation pages 6-8) | Ribosome recycling coupled to selective re-entry into scanning and downstream translation (bohlen2023humanmcts1dependenttranslation pages 5-6, bohlen2023humanmcts1dependenttranslation pages 6-8) |
| Selective translational activator of JAK2 | MCTS1 is required for efficient translation through the JAK2 5′UTR, which contains three uORFs, including two ultra-short start-stop uORFs; MCTS1 deficiency lowers JAK2 protein by ~3–5-fold without changing JAK2 mRNA, indicating translational rather than transcriptional control (bohlen2023humanmcts1dependenttranslation pages 8-9, bohlen2023humanmcts1dependenttranslation pages 1-3) | JAK2 mRNA is the best-defined physiologic target in human disease; among IFN-γ-immunity genes tested, JAK2 showed the strongest specific dependence on MCTS1-dependent re-initiation (bohlen2023humanmcts1dependenttranslation pages 6-8, bohlen2023humanmcts1dependenttranslation pages 8-9) | Cytoplasmic translation machinery in fibroblasts, T cells, phagocytes, and THP-1 cells; effect observed across multiple cell types (bohlen2023humanmcts1dependenttranslation pages 1-3, bohlen2023humanmcts1dependenttranslation pages 8-9) | IL-23/JAK2/STAT and partly IL-12/JAK2 signaling; reduced JAK2 translation impairs IL-23-driven IFN-γ production and causes Mendelian susceptibility to mycobacterial disease (bohlen2023humanmcts1dependenttranslation pages 1-3, bohlen2023humanmcts1dependenttranslation pages 8-9) |
| Regulator of immune effector competence via translational control | By sustaining JAK2 translation, MCTS1 enables cytokine signaling needed for antimycobacterial immunity; MCTS1 deficiency selectively compromises IL-23-dependent IFN-γ induction in innate-like adaptive lymphocytes despite relatively preserved broader physiology (bohlen2023humanmcts1dependenttranslation pages 1-3, bohlen2023humanmcts1dependenttranslation pages 8-9) | MAIT cells, γδ T cells, and other IFN-γ-producing lymphocyte subsets are functionally affected downstream of reduced JAK2 protein; whole blood from deficient patients shows markedly reduced BCG-induced IFN-γ (bohlen2023humanmcts1dependenttranslation pages 1-3, bohlen2023humanmcts1dependenttranslation pages 8-9) | Functional action is intracellular/cytoplasmic, but physiological output is measured in immune cells and whole blood (bohlen2023humanmcts1dependenttranslation pages 1-3, bohlen2023humanmcts1dependenttranslation pages 8-9) | Host defense against mycobacteria; IL-23-dependent induction of IFN-γ is the clearest disease-relevant pathway linked to MCTS1 (bohlen2023humanmcts1dependenttranslation pages 1-3, bohlen2023humanmcts1dependenttranslation pages 8-9) |
| Stress-responsive translational regulator | MCTS1 participates in noncanonical initiation/re-initiation mechanisms that support ATF4 protein induction during stress; MYC-driven PUS7-dependent pseudouridylation can enhance MCTS1 translation, placing MCTS1 in a stress-adaptation circuit (ding2024mycdrivesmrna pages 1-2, vasudevan2020translationalinductionof pages 1-2) | ATF4 mRNA and other ISR-responsive uORF-regulated transcripts; evidence supports overlap with DENR/eIF2D-dependent ATF4 control in stressed cells (ding2024mycdrivesmrna pages 1-2, vasudevan2020translationalinductionof pages 1-2) | Cytoplasmic translation apparatus in stressed cells (ding2024mycdrivesmrna pages 1-2, vasudevan2020translationalinductionof pages 1-2) | Integrated Stress Response (ISR), ATF4 induction, adaptation to amino acid/ER and proliferative stress (ding2024mycdrivesmrna pages 1-2, vasudevan2020translationalinductionof pages 1-2) |
| Cell-cycle regulated translation factor through its DENR partner complex | DENR is phosphorylated by Cyclin B/CDK1 and Cyclin A/CDK2 in mitosis, stabilizing the DENR·MCTS1 complex and enhancing translation of mitotically relevant mRNAs; this links MCTS1-mediated re-initiation to mitotic protein synthesis and faithful division (hohenberg2022cyclinbcdk1and pages 1-2) | A substantial fraction of mRNAs with elevated translation in mitosis are DENR targets, implying functional action of the DENR·MCTS1 complex on mitotic transcripts enriched for relevant uORF features (hohenberg2022cyclinbcdk1and pages 1-2) | Cytoplasmic/ribosome-associated during cell-cycle progression, especially mitosis (hohenberg2022cyclinbcdk1and pages 1-2) | Mitotic translational control; Cyclin/CDK-dependent regulation of selective protein synthesis for cell division (hohenberg2022cyclinbcdk1and pages 1-2) |
| Oncogenic translational and protein-network modulator | In cancer contexts, elevated MCTS1 promotes aggressive phenotypes by stimulating selective translation programs and, in some settings, stabilizing oncogenic partners such as PA2G4-P48; prior work also links MCTS1 to IL-6/IL-6R/STAT3-associated stemness and EMT phenotypes (sun2023proliferationassociated2g4p48 pages 1-2, weng2019mct1mir34ail6il6rsignalingaxis pages 1-2) | PA2G4-P48 protein stability in HNSCC; cyclin D1 and c-Myc translation in luminal breast cancer; broader cancer-associated uORF-controlled transcripts (sun2023proliferationassociated2g4p48 pages 1-2, weng2019mct1mir34ail6il6rsignalingaxis pages 1-2) | Primarily cytoplasmic, where translation and proteostasis effects are exerted (sun2023proliferationassociated2g4p48 pages 1-2, weng2019mct1mir34ail6il6rsignalingaxis pages 1-2) | Cancer-associated translational rewiring; IL-6/IL-6R/STAT3, EMT/stemness programs, and proliferative signaling indirectly influenced by MCTS1-driven expression control (sun2023proliferationassociated2g4p48 pages 1-2, weng2019mct1mir34ail6il6rsignalingaxis pages 1-2) |
Table: This table summarizes the current evidence for human MCTS1 as a cytoplasmic, ribosome-associated non-canonical translation re-initiation factor. It highlights its DENR partnership, mechanism on uORF-containing transcripts, key targets such as JAK2 and ATF4, and its roles in immunity, stress responses, mitosis, and cancer.
| Molecular Function | Mechanism of Action | Substrate/Targets | Subcellular Localization | Key Pathways |
|---|---|---|---|---|
| Non-canonical translation re-initiation factor | MCTS1 forms a heterodimer with DENR and acts on post-termination 40S ribosomal subunits to promote re-initiation after translation of upstream open reading frames (uORFs); proposed activities include removal of deacylated P-site tRNA and/or delivery of a new initiator tRNA, thereby restoring scanning competence for downstream CDS translation (meurs2024aninvitro pages 1-4, meurs2025mcts2anddistinct pages 1-2, meurs2025mcts2anddistinct pages 2-3) | uORF-containing transcripts as a selective class; DENR-responsive transcripts are enriched for translated uORFs, including both 1-aa/start-stop and longer uORFs (meurs2024aninvitro pages 4-7, meurs2025mcts2anddistinct pages 2-3) | Cytoplasmic, ribosome-associated; binds the small ribosomal subunit/40S and functions on translating ribosomes during re-initiation and ribosome recycling (casteloszekely2019chartingdenrdependenttranslation pages 1-2, hohenberg2022cyclinbcdk1and pages 1-2, weng2019mct1mir34ail6il6rsignalingaxis pages 1-2) | Core translational control pathway governing uORF-dependent re-initiation and selective protein synthesis (meurs2024aninvitro pages 1-4, sriram2018translationacrobaticshow pages 1-2) |
| Ribosome recycling factor in the DENR-MCTS1 complex | After ORF termination, the DENR-MCTS1 complex removes tRNA from 40S ribosomes; 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 (bohlen2023humanmcts1dependenttranslation pages 5-6, bohlen2023humanmcts1dependenttranslation pages 6-8) | Post-termination 40S ribosomes on main ORFs and uORFs; stop-codon contexts with certain penultimate codons show stronger dependence (bohlen2023humanmcts1dependenttranslation pages 5-6, bohlen2023humanmcts1dependenttranslation pages 6-8, meurs2025mcts2anddistinct pages 2-3) | Cytoplasmic, on mRNA-bound ribosomes during translation termination/recycling (bohlen2023humanmcts1dependenttranslation pages 5-6, bohlen2023humanmcts1dependenttranslation pages 6-8) | Ribosome recycling coupled to selective re-entry into scanning and downstream translation (bohlen2023humanmcts1dependenttranslation pages 5-6, bohlen2023humanmcts1dependenttranslation pages 6-8) |
| Selective translational activator of JAK2 | MCTS1 is required for efficient translation through the JAK2 5′UTR, which contains three uORFs, including two ultra-short start-stop uORFs; MCTS1 deficiency lowers JAK2 protein by ~3–5-fold without changing JAK2 mRNA, indicating translational rather than transcriptional control (bohlen2023humanmcts1dependenttranslation pages 8-9, bohlen2023humanmcts1dependenttranslation pages 1-3) | JAK2 mRNA is the best-defined physiologic target in human disease; among IFN-γ-immunity genes tested, JAK2 showed the strongest specific dependence on MCTS1-dependent re-initiation (bohlen2023humanmcts1dependenttranslation pages 6-8, bohlen2023humanmcts1dependenttranslation pages 8-9) | Cytoplasmic translation machinery in fibroblasts, T cells, phagocytes, and THP-1 cells; effect observed across multiple cell types (bohlen2023humanmcts1dependenttranslation pages 1-3, bohlen2023humanmcts1dependenttranslation pages 8-9) | IL-23/JAK2/STAT and partly IL-12/JAK2 signaling; reduced JAK2 translation impairs IL-23-driven IFN-γ production and causes Mendelian susceptibility to mycobacterial disease (bohlen2023humanmcts1dependenttranslation pages 1-3, bohlen2023humanmcts1dependenttranslation pages 8-9) |
| Regulator of immune effector competence via translational control | By sustaining JAK2 translation, MCTS1 enables cytokine signaling needed for antimycobacterial immunity; MCTS1 deficiency selectively compromises IL-23-dependent IFN-γ induction in innate-like adaptive lymphocytes despite relatively preserved broader physiology (bohlen2023humanmcts1dependenttranslation pages 1-3, bohlen2023humanmcts1dependenttranslation pages 8-9) | MAIT cells, γδ T cells, and other IFN-γ-producing lymphocyte subsets are functionally affected downstream of reduced JAK2 protein; whole blood from deficient patients shows markedly reduced BCG-induced IFN-γ (bohlen2023humanmcts1dependenttranslation pages 1-3, bohlen2023humanmcts1dependenttranslation pages 8-9) | Functional action is intracellular/cytoplasmic, but physiological output is measured in immune cells and whole blood (bohlen2023humanmcts1dependenttranslation pages 1-3, bohlen2023humanmcts1dependenttranslation pages 8-9) | Host defense against mycobacteria; IL-23-dependent induction of IFN-γ is the clearest disease-relevant pathway linked to MCTS1 (bohlen2023humanmcts1dependenttranslation pages 1-3, bohlen2023humanmcts1dependenttranslation pages 8-9) |
| Stress-responsive translational regulator | MCTS1 participates in noncanonical initiation/re-initiation mechanisms that support ATF4 protein induction during stress; MYC-driven PUS7-dependent pseudouridylation can enhance MCTS1 translation, placing MCTS1 in a stress-adaptation circuit (ding2024mycdrivesmrna pages 1-2, vasudevan2020translationalinductionof pages 1-2) | ATF4 mRNA and other ISR-responsive uORF-regulated transcripts; evidence supports overlap with DENR/eIF2D-dependent ATF4 control in stressed cells (ding2024mycdrivesmrna pages 1-2, vasudevan2020translationalinductionof pages 1-2) | Cytoplasmic translation apparatus in stressed cells (ding2024mycdrivesmrna pages 1-2, vasudevan2020translationalinductionof pages 1-2) | Integrated Stress Response (ISR), ATF4 induction, adaptation to amino acid/ER and proliferative stress (ding2024mycdrivesmrna pages 1-2, vasudevan2020translationalinductionof pages 1-2) |
| Cell-cycle regulated translation factor through its DENR partner complex | DENR is phosphorylated by Cyclin B/CDK1 and Cyclin A/CDK2 in mitosis, stabilizing the DENR·MCTS1 complex and enhancing translation of mitotically relevant mRNAs; this links MCTS1-mediated re-initiation to mitotic protein synthesis and faithful division (hohenberg2022cyclinbcdk1and pages 1-2) | A substantial fraction of mRNAs with elevated translation in mitosis are DENR targets, implying functional action of the DENR·MCTS1 complex on mitotic transcripts enriched for relevant uORF features (hohenberg2022cyclinbcdk1and pages 1-2) | Cytoplasmic/ribosome-associated during cell-cycle progression, especially mitosis (hohenberg2022cyclinbcdk1and pages 1-2) | Mitotic translational control; Cyclin/CDK-dependent regulation of selective protein synthesis for cell division (hohenberg2022cyclinbcdk1and pages 1-2) |
| Oncogenic translational and protein-network modulator | In cancer contexts, elevated MCTS1 promotes aggressive phenotypes by stimulating selective translation programs and, in some settings, stabilizing oncogenic partners such as PA2G4-P48; prior work also links MCTS1 to IL-6/IL-6R/STAT3-associated stemness and EMT phenotypes (sun2023proliferationassociated2g4p48 pages 1-2, weng2019mct1mir34ail6il6rsignalingaxis pages 1-2) | PA2G4-P48 protein stability in HNSCC; cyclin D1 and c-Myc translation in luminal breast cancer; broader cancer-associated uORF-controlled transcripts (sun2023proliferationassociated2g4p48 pages 1-2, weng2019mct1mir34ail6il6rsignalingaxis pages 1-2) | Primarily cytoplasmic, where translation and proteostasis effects are exerted (sun2023proliferationassociated2g4p48 pages 1-2, weng2019mct1mir34ail6il6rsignalingaxis pages 1-2) | Cancer-associated translational rewiring; IL-6/IL-6R/STAT3, EMT/stemness programs, and proliferative signaling indirectly influenced by MCTS1-driven expression control (sun2023proliferationassociated2g4p48 pages 1-2, weng2019mct1mir34ail6il6rsignalingaxis pages 1-2) |
Table: This table summarizes the current evidence for human MCTS1 as a cytoplasmic, ribosome-associated non-canonical translation re-initiation factor. It highlights its DENR partnership, mechanism on uORF-containing transcripts, key targets such as JAK2 and ATF4, and its roles in immunity, stress responses, mitosis, and cancer.
For additional details, consult cited primary literature above.
References
(meurs2024aninvitro pages 1-4): Romane Meurs, Mara De Matos, Adrian Bothe, Nicolas Guex, Tobias Weber, Aurelio A. Teleman, Nenad Ban, and David Gatfield. An in vitro assay of mcts1-denr-dependent re-initiation and ribosome profiling uncover the activity of mcts2 and distinct function of eif2d. bioRxiv, Jun 2024. URL: https://doi.org/10.1101/2024.06.05.597545, doi:10.1101/2024.06.05.597545. This article has 3 citations.
(meurs2025mcts2anddistinct pages 1-2): Romane Meurs, Mara De Matos, Adrian Bothe, Nicolas Guex, Tobias Weber, Aurelio A Teleman, Nenad Ban, and David Gatfield. Mcts2 and distinct eif2d roles in uorf-dependent translation regulation revealed by in vitro re-initiation assays. The EMBO Journal, 44:854-876, Jan 2025. URL: https://doi.org/10.1038/s44318-024-00347-3, doi:10.1038/s44318-024-00347-3. This article has 3 citations.
(meurs2025mcts2anddistinct pages 2-3): Romane Meurs, Mara De Matos, Adrian Bothe, Nicolas Guex, Tobias Weber, Aurelio A Teleman, Nenad Ban, and David Gatfield. Mcts2 and distinct eif2d roles in uorf-dependent translation regulation revealed by in vitro re-initiation assays. The EMBO Journal, 44:854-876, Jan 2025. URL: https://doi.org/10.1038/s44318-024-00347-3, doi:10.1038/s44318-024-00347-3. This article has 3 citations.
(meurs2024aninvitro pages 4-7): Romane Meurs, Mara De Matos, Adrian Bothe, Nicolas Guex, Tobias Weber, Aurelio A. Teleman, Nenad Ban, and David Gatfield. An in vitro assay of mcts1-denr-dependent re-initiation and ribosome profiling uncover the activity of mcts2 and distinct function of eif2d. bioRxiv, Jun 2024. URL: https://doi.org/10.1101/2024.06.05.597545, doi:10.1101/2024.06.05.597545. This article has 3 citations.
(casteloszekely2019chartingdenrdependenttranslation pages 1-2): Violeta Castelo-Szekely, Mara De Matos, Marina Tusup, Steve Pascolo, Jernej Ule, and David Gatfield. Charting denr-dependent translation reinitiation uncovers predictive uorf features and links to circadian timekeeping via clock. Nucleic Acids Research, 47:5193-5209, Sep 2019. URL: https://doi.org/10.1093/nar/gkz261, doi:10.1093/nar/gkz261. This article has 47 citations and is from a highest quality peer-reviewed journal.
(hohenberg2022cyclinbcdk1and pages 1-2): Katharina Clemm von Hohenberg, Sandra Müller, Sibylle Schleich, Matthias Meister, Jonathan Bohlen, Thomas G. Hofmann, and Aurelio A. Teleman. Cyclin b/cdk1 and cyclin a/cdk2 phosphorylate denr to promote mitotic protein translation and faithful cell division. Nature Communications, Feb 2022. URL: https://doi.org/10.1038/s41467-022-28265-0, doi:10.1038/s41467-022-28265-0. This article has 48 citations and is from a highest quality peer-reviewed journal.
(weng2019mct1mir34ail6il6rsignalingaxis pages 1-2): Yueh-Shan Weng, Hong-Yu Tseng, Yen-An Chen, Pei-Chun Shen, Aushia Tanzih Al Haq, Li-Mei Chen, Yi-Chung Tung, and Hsin-Ling Hsu. Mct-1/mir-34a/il-6/il-6r signaling axis promotes emt progression, cancer stemness and m2 macrophage polarization in triple-negative breast cancer. Molecular Cancer, Mar 2019. URL: https://doi.org/10.1186/s12943-019-0988-0, doi:10.1186/s12943-019-0988-0. This article has 448 citations and is from a highest quality peer-reviewed journal.
(sriram2018translationacrobaticshow pages 1-2): Ashwin Sriram, Jonathan Bohlen, and Aurelio A Teleman. Translation acrobatics: how cancer cells exploit alternate modes of translational initiation. EMBO reports, Sep 2018. URL: https://doi.org/10.15252/embr.201845947, doi:10.15252/embr.201845947. This article has 128 citations and is from a highest quality peer-reviewed journal.
(bohlen2023humanmcts1dependenttranslation pages 5-6): Jonathan Bohlen, Qinhua Zhou, Quentin Philippot, Masato Ogishi, Darawan Rinchai, Tea Nieminen, Simin Seyedpour, Nima Parvaneh, Nima Rezaei, Niloufar Yazdanpanah, Mana Momenilandi, Clément Conil, Anna-Lena Neehus, Carltin Schmidt, Carlos A. Arango-Franco, Tom Le Voyer, Taushif Khan, Rui Yang, Julia Puchan, Lucia Erazo, Mykola Roiuk, Taja Vatovec, Zarah Janda, Ivan Bagarić, Marie Materna, Adrian Gervais, Hailun Li, Jérémie Rosain, Jessica N Peel, Yoann Seeleuthner, Ji Eun Han, Anne-Sophie L’Honneur, Marcela Moncada-Vélez, Marta Martin-Fernandez, Michael E. Horesh, Tatiana Kochetkov, Monika Schmidt, Mohammed A. AlShehri, Eeva Salo, Harri Saxen, Gehad ElGhazali, Ahmad Yatim, Camille Soudée, Federica Sallusto, Armin Ensser, Nico Marr, Peng Zhang, Dusan Bogunovic, Aurélie Cobat, Mohammad Shahrooei, Vivien Béziat, Laurent Abel, Xiaochuan Wang, Stéphanie Boisson-Dupuis, Aurelio A. Teleman, Jacinta Bustamante, Qian Zhang, and Jean-Laurent Casanova. Human mcts1-dependent translation of jak2 is essential for ifn-γ immunity to mycobacteria. Cell, 186:5114-5134.e27, Nov 2023. URL: https://doi.org/10.1016/j.cell.2023.09.024, doi:10.1016/j.cell.2023.09.024. This article has 45 citations and is from a highest quality peer-reviewed journal.
(bohlen2023humanmcts1dependenttranslation pages 6-8): Jonathan Bohlen, Qinhua Zhou, Quentin Philippot, Masato Ogishi, Darawan Rinchai, Tea Nieminen, Simin Seyedpour, Nima Parvaneh, Nima Rezaei, Niloufar Yazdanpanah, Mana Momenilandi, Clément Conil, Anna-Lena Neehus, Carltin Schmidt, Carlos A. Arango-Franco, Tom Le Voyer, Taushif Khan, Rui Yang, Julia Puchan, Lucia Erazo, Mykola Roiuk, Taja Vatovec, Zarah Janda, Ivan Bagarić, Marie Materna, Adrian Gervais, Hailun Li, Jérémie Rosain, Jessica N Peel, Yoann Seeleuthner, Ji Eun Han, Anne-Sophie L’Honneur, Marcela Moncada-Vélez, Marta Martin-Fernandez, Michael E. Horesh, Tatiana Kochetkov, Monika Schmidt, Mohammed A. AlShehri, Eeva Salo, Harri Saxen, Gehad ElGhazali, Ahmad Yatim, Camille Soudée, Federica Sallusto, Armin Ensser, Nico Marr, Peng Zhang, Dusan Bogunovic, Aurélie Cobat, Mohammad Shahrooei, Vivien Béziat, Laurent Abel, Xiaochuan Wang, Stéphanie Boisson-Dupuis, Aurelio A. Teleman, Jacinta Bustamante, Qian Zhang, and Jean-Laurent Casanova. Human mcts1-dependent translation of jak2 is essential for ifn-γ immunity to mycobacteria. Cell, 186:5114-5134.e27, Nov 2023. URL: https://doi.org/10.1016/j.cell.2023.09.024, doi:10.1016/j.cell.2023.09.024. This article has 45 citations and is from a highest quality peer-reviewed journal.
(bohlen2023humanmcts1dependenttranslation pages 8-9): Jonathan Bohlen, Qinhua Zhou, Quentin Philippot, Masato Ogishi, Darawan Rinchai, Tea Nieminen, Simin Seyedpour, Nima Parvaneh, Nima Rezaei, Niloufar Yazdanpanah, Mana Momenilandi, Clément Conil, Anna-Lena Neehus, Carltin Schmidt, Carlos A. Arango-Franco, Tom Le Voyer, Taushif Khan, Rui Yang, Julia Puchan, Lucia Erazo, Mykola Roiuk, Taja Vatovec, Zarah Janda, Ivan Bagarić, Marie Materna, Adrian Gervais, Hailun Li, Jérémie Rosain, Jessica N Peel, Yoann Seeleuthner, Ji Eun Han, Anne-Sophie L’Honneur, Marcela Moncada-Vélez, Marta Martin-Fernandez, Michael E. Horesh, Tatiana Kochetkov, Monika Schmidt, Mohammed A. AlShehri, Eeva Salo, Harri Saxen, Gehad ElGhazali, Ahmad Yatim, Camille Soudée, Federica Sallusto, Armin Ensser, Nico Marr, Peng Zhang, Dusan Bogunovic, Aurélie Cobat, Mohammad Shahrooei, Vivien Béziat, Laurent Abel, Xiaochuan Wang, Stéphanie Boisson-Dupuis, Aurelio A. Teleman, Jacinta Bustamante, Qian Zhang, and Jean-Laurent Casanova. Human mcts1-dependent translation of jak2 is essential for ifn-γ immunity to mycobacteria. Cell, 186:5114-5134.e27, Nov 2023. URL: https://doi.org/10.1016/j.cell.2023.09.024, doi:10.1016/j.cell.2023.09.024. This article has 45 citations and is from a highest quality peer-reviewed journal.
(bohlen2023humanmcts1dependenttranslation pages 1-3): Jonathan Bohlen, Qinhua Zhou, Quentin Philippot, Masato Ogishi, Darawan Rinchai, Tea Nieminen, Simin Seyedpour, Nima Parvaneh, Nima Rezaei, Niloufar Yazdanpanah, Mana Momenilandi, Clément Conil, Anna-Lena Neehus, Carltin Schmidt, Carlos A. Arango-Franco, Tom Le Voyer, Taushif Khan, Rui Yang, Julia Puchan, Lucia Erazo, Mykola Roiuk, Taja Vatovec, Zarah Janda, Ivan Bagarić, Marie Materna, Adrian Gervais, Hailun Li, Jérémie Rosain, Jessica N Peel, Yoann Seeleuthner, Ji Eun Han, Anne-Sophie L’Honneur, Marcela Moncada-Vélez, Marta Martin-Fernandez, Michael E. Horesh, Tatiana Kochetkov, Monika Schmidt, Mohammed A. AlShehri, Eeva Salo, Harri Saxen, Gehad ElGhazali, Ahmad Yatim, Camille Soudée, Federica Sallusto, Armin Ensser, Nico Marr, Peng Zhang, Dusan Bogunovic, Aurélie Cobat, Mohammad Shahrooei, Vivien Béziat, Laurent Abel, Xiaochuan Wang, Stéphanie Boisson-Dupuis, Aurelio A. Teleman, Jacinta Bustamante, Qian Zhang, and Jean-Laurent Casanova. Human mcts1-dependent translation of jak2 is essential for ifn-γ immunity to mycobacteria. Cell, 186:5114-5134.e27, Nov 2023. URL: https://doi.org/10.1016/j.cell.2023.09.024, doi:10.1016/j.cell.2023.09.024. This article has 45 citations and is from a highest quality peer-reviewed journal.
(ding2024mycdrivesmrna pages 1-2): Jane Ding, Mohit Bansal, Yuxia Cao, Bingwei Ye, Rui Mao, Anamika Gupta, Sunil Sudarshan, and Han-Fei Ding. Myc drives mrna pseudouridylation to mitigate proliferation-induced cellular stress during cancer development. Cancer Research, 84:4031-4048, Sep 2024. URL: https://doi.org/10.1158/0008-5472.can-24-1102, doi:10.1158/0008-5472.can-24-1102. This article has 26 citations and is from a highest quality peer-reviewed journal.
(vasudevan2020translationalinductionof pages 1-2): Deepika Vasudevan, Sarah D. Neuman, Amy Yang, Lea Lough, Brian Brown, Arash Bashirullah, Timothy Cardozo, and Hyung Don Ryoo. Translational induction of atf4 during integrated stress response requires noncanonical initiation factors eif2d and denr. Nature Communications, Sep 2020. URL: https://doi.org/10.1038/s41467-020-18453-1, doi:10.1038/s41467-020-18453-1. This article has 113 citations and is from a highest quality peer-reviewed journal.
(sun2023proliferationassociated2g4p48 pages 1-2): Legang Sun, Guoyi Xing, Wenlong Wang, Xiangrui Ma, and Xiangbin Bu. Proliferation-associated 2g4 p48 is stabilized by malignant t-cell amplified sequence 1 and promotes the proliferation of head and neck squamous cell carcinoma. Journal of Dental Sciences, 18(4):1588-1597, Oct 2023. URL: https://doi.org/10.1016/j.jds.2023.02.020, doi:10.1016/j.jds.2023.02.020. This article has 5 citations and is from a peer-reviewed journal.
(bohlen2023humanmcts1dependenttranslation pages 3-5): Jonathan Bohlen, Qinhua Zhou, Quentin Philippot, Masato Ogishi, Darawan Rinchai, Tea Nieminen, Simin Seyedpour, Nima Parvaneh, Nima Rezaei, Niloufar Yazdanpanah, Mana Momenilandi, Clément Conil, Anna-Lena Neehus, Carltin Schmidt, Carlos A. Arango-Franco, Tom Le Voyer, Taushif Khan, Rui Yang, Julia Puchan, Lucia Erazo, Mykola Roiuk, Taja Vatovec, Zarah Janda, Ivan Bagarić, Marie Materna, Adrian Gervais, Hailun Li, Jérémie Rosain, Jessica N Peel, Yoann Seeleuthner, Ji Eun Han, Anne-Sophie L’Honneur, Marcela Moncada-Vélez, Marta Martin-Fernandez, Michael E. Horesh, Tatiana Kochetkov, Monika Schmidt, Mohammed A. AlShehri, Eeva Salo, Harri Saxen, Gehad ElGhazali, Ahmad Yatim, Camille Soudée, Federica Sallusto, Armin Ensser, Nico Marr, Peng Zhang, Dusan Bogunovic, Aurélie Cobat, Mohammad Shahrooei, Vivien Béziat, Laurent Abel, Xiaochuan Wang, Stéphanie Boisson-Dupuis, Aurelio A. Teleman, Jacinta Bustamante, Qian Zhang, and Jean-Laurent Casanova. Human mcts1-dependent translation of jak2 is essential for ifn-γ immunity to mycobacteria. Cell, 186:5114-5134.e27, Nov 2023. URL: https://doi.org/10.1016/j.cell.2023.09.024, doi:10.1016/j.cell.2023.09.024. This article has 45 citations and is from a highest quality peer-reviewed journal.
UniProt Q9ULC4. Contains a PUA domain (RNA-binding). Partner of DENR; the MCTS1-DENR heterodimer is the eIF2D-like non-canonical reinitiation/recycling factor (MCTS1 = N-terminal half of Ligatin/eIF2D, DENR = C-terminal SUI1 half).
*-deep-research*.md file found in this gene directory.no_mapping, so no contradiction is projected onto MCTS1.no_mapping; do not project GO:0006415 onto MCTS1 (it is post-termination recycling, not termination).Translation|Cytosolic translation|Translation termination|tRNA, mRNA release ; PN-node mapping: type=no_mapping (no GO); only the parent group "Translation termination" is mapped (GO:0006415 translational termination, ok_for_propagation), with the class/branch context_only.no_mapping, so no contradiction is projected onto MCTS1.no_mapping is correct — MCTS1 release/recycling is not the same as the group's GO:0006415 termination. The group-level GO:0006415 projection (which MCTS1 does not inherit) is reasonable for true eRF/release-factor members but would be a mis-annotation if applied to MCTS1; current scoping correctly avoids that.no_mapping; do not project GO:0006415 onto MCTS1 (it is post-termination recycling, not termination).This file is generated from the current PROTEOSTASIS phase-1 dossier and local gene-review artifacts. Edit the source review, PN mapping, or dossier rather than this generated note when correcting the underlying curation.
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.