Affinage

THOC2

THO complex subunit 2 · UniProt Q8NI27

Length
1593 aa
Mass
182.8 kDa
Annotated
2026-06-10
22 papers in source corpus 14 papers cited in narrative 14 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

THOC2 is the largest subunit of the conserved nuclear THO/TREX complex that couples RNA polymerase II transcription elongation to co-transcriptional mRNP assembly and nuclear mRNA export; the yeast ortholog (Tho2/Rlr1) was first defined as a component of an oligomeric complex with Hpr1, Mft1, and Thp2 and shown to act at a step downstream of transcription initiation, where its loss reduces elongation efficiency and promotes transcription-dependent hyper-recombination (PMID:11060033, PMID:9707445, PMID:10675628). THOC2 links transcription to mRNP biogenesis through the DEAD-box helicase Sub2/UAP56, which lies in the same export pathway (PMID:12034490), and its function further supports transcription-coupled nucleotide excision repair (PMID:12000839). THOC2 stability is essential for the integrity of the entire TREX complex: destabilizing variants of THOC2 trigger downstream loss of partner subunits THOC1, THOC5, THOC6, and THOC7, with the C-terminal RNA-binding domain being critical for complex assembly (PMID:26166480, PMID:29851191, PMID:32116545). Loss-of-function THOC2 variants cause X-linked intellectual disability and broader neurodevelopmental disorder, and a hypomorphic mouse model establishes that compromised THOC2/TREX function drives R-loop accumulation, DNA damage, and cell death during brain development as the molecular basis of THOC2 syndrome (PMID:26166480, PMID:38331934). Beyond its core complex role, Tho2 can act independently of other THO subunits—recruiting the RNA exosome subunit Rrp6 to chromatin via its C-terminal domain for cotranscriptional mRNP quality control and escorting the terminator Nrd1 on chromatin (PMID:37914399, PMID:38769776). In cancer contexts, THOC2 promotes nuclear export of SOX2 and NANOG transcripts to sustain stem-like properties and radioresistance, and influences Bcl-x alternative splicing and L1CAM expression (PMID:34708581, PMID:37424800).

Mechanistic history

Synthesis pass · year-by-year structured walk · 10 steps
  1. 1998 High

    Established that THO2 acts within transcription itself rather than only downstream, answering whether the gene affects mRNA production at the elongation step and linking elongation defects to genome instability.

    Evidence In vivo transcription and recombination assays in tho2Δ yeast

    PMID:9707445

    Open questions at the time
    • Did not define the physical complex mediating the effect
    • Mechanism connecting elongation to recombination not resolved
  2. 2000 High

    Defined the physical THO complex and placed THO2 at a step subsequent to initiation, establishing the molecular assembly through which it couples transcription to recombination.

    Evidence Affinity purification and reciprocal Co-IP of Tho2 with Hpr1/Mft1/Thp2; genetic suppressor screen against sin4

    PMID:10675628 PMID:11060033

    Open questions at the time
    • Stoichiometry and architecture of the complex not determined
    • Direct RNA-binding role of Tho2 not shown
  3. 2002 Medium

    Connected the THO complex to mRNA export and DNA repair, showing THO2 links transcription to Sub2-mediated mRNP assembly and supports transcription-coupled repair.

    Evidence Dosage suppressor screen with sub2; UV survival and T4 endo V repair assays in tho2Δ/hpr1Δ yeast

    PMID:12000839 PMID:12034490

    Open questions at the time
    • Direct physical interaction between Tho2 and Sub2 not demonstrated
    • Whether repair defect is secondary to elongation/export defect unresolved
  4. 2013 Medium

    Extended THOC2 function to metazoan neuronal biology, showing loss-of-function alters neurite extension, stem cell growth, and sensory neuron function across model systems.

    Evidence Thoc2 knockdown in rat neurons and neuronal stem cells; C. elegans ortholog knockout

    PMID:23749989

    Open questions at the time
    • Molecular link between RNA export and neuronal phenotype not defined
    • No human disease connection established here
  5. 2015 High

    Identified THOC2 as a human X-linked intellectual disability gene and showed the disease mechanism is destabilization of THOC2 and its TREX partners, mapping affected residues to RNA-binding domains.

    Evidence X-exome sequencing, patient-cell protein stability assays, structural modeling

    PMID:26166480

    Open questions at the time
    • Downstream transcriptomic consequences in patient neurons not characterized
    • Genotype-phenotype relationship across variants incomplete
  6. 2018 High

    Broadened the variant spectrum and confirmed that reduced THOC2 stability propagates to destabilize the wider TREX complex (THOC1/5/6/7), reinforcing the stability-based disease mechanism.

    Evidence Patient-derived cell stability assays for THOC2 and multiple TREX subunits; splice/truncation variant analysis

    PMID:29851191

    Open questions at the time
    • Functional RNA-export defect not directly quantified
    • How partial complex destabilization maps to phenotype severity unknown
  7. 2020 High

    Pinpointed the C-terminal RNA-binding domain as functionally critical for complex integrity, refining which structural region underlies pathogenic destabilization.

    Evidence Ex vivo testing of 14 variants and intragenic deletions in patient cells with TREX subunit stability readouts

    PMID:32116545

    Open questions at the time
    • Atomic structure of the C-terminal RBD not resolved
    • RNA targets bound by this domain not identified
  8. 2021 Medium

    Revealed a cancer-relevant export function, showing THOC2 drives nuclear export of stemness transcripts SOX2 and NANOG to confer stem-like properties and radioresistance.

    Evidence THOC2/THOC5 knockdown with RNA fractionation, protein analysis, and xenografts in TNBC

    PMID:34708581

    Open questions at the time
    • Selectivity for specific transcripts mechanistically unexplained
    • Single-lab finding without independent replication
  9. 2023 Medium

    Uncovered a THO-complex-independent role for Tho2 in mRNP quality control and demonstrated splicing/adhesion consequences of THOC2 loss in cancer cells.

    Evidence Genome-wide ChIP-seq of THO subunits under mRNP perturbation with C-terminal domain mapping (yeast); shRNA knockdown with RNA-seq splicing analysis (GBM)

    PMID:37424800 PMID:37914399

    Open questions at the time
    • Whether the exosome-recruiting role is conserved in human THOC2 untested
    • Direct binding of Tho2 C-terminus to Rrp6 not biochemically reconstituted
  10. 2024 Medium

    Established R-loop dysregulation as the in vivo molecular mechanism of THOC2 syndrome and linked Tho2 to terminator escort and lifespan control.

    Evidence Hypomorphic Thoc2 mouse with R-loop/DNA-damage and behavioral assays; Nrd1 ChIP-seq and lifespan assays in yeast

    PMID:38331934 PMID:38769776

    Open questions at the time
    • Causal chain from R-loops to specific neuronal cell death not fully resolved
    • Whether Nrd1-escort function is conserved beyond yeast unknown

Open questions

Synthesis pass · forward-looking unresolved questions
  • How THOC2 selects specific transcripts for export and quality control, and how this transcript selectivity translates into tissue-specific neurodevelopmental and oncogenic outcomes, remains unresolved.
  • No structural model of human THOC2 within assembled TREX
  • RNA-binding specificity of THOC2 not mapped
  • Mechanism of THO-independent functions in human cells uncharacterized

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0003723 RNA binding 2
Localization
GO:0005694 chromosome 2 GO:0005634 nucleus 1
Pathway
R-HSA-8953854 Metabolism of RNA 3 R-HSA-73894 DNA Repair 2 R-HSA-74160 Gene expression (Transcription) 2
Partners
MFT1SUB2THOC1THOC5THOC6THOC7THP2
Complex memberships
THO/TREX complex

Evidence

Reading pass · 14 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2000 THOC2 (Tho2) is a component of a nuclear oligomeric protein complex containing Hpr1, Mft1, and Thp2, physically associated via co-immunoprecipitation; this complex connects transcription elongation with mitotic recombination in yeast. Affinity purification (His6-HA-tagged Tho2), reciprocal co-immunoprecipitation with anti-Mft1 antibodies, genetic analysis of deletion mutants The EMBO journal High 11060033
1998 THO2 is required for RNA polymerase II-dependent transcription elongation; tho2Δ reduces transcriptional efficiency and abolishes transcription through the lacZ sequence, and causes hyper-recombination between direct repeats in a transcription-dependent manner. In vivo transcriptional analysis of tho2Δ cells, recombination frequency assays, transcription-dependent recombination genetic analysis The EMBO journal High 9707445
2000 RLR1 (THO2) functions in transcription at a step subsequent to initiation; rlr1 mutants specifically fail to express lacZ fusions while expressing native chromosomal genes at near-normal levels; RLR1 was isolated as a suppressor of SIN4 (a Mediator subcomplex component), placing THO2 in a pathway downstream of transcription initiation. Genetic suppressor screen (rlr1-1 as suppressor of sin4 mutation), lacZ reporter assays, epistasis analysis Gene Medium 10675628
2002 The DEAD-box RNA helicase Sub2 is a dosage-dependent suppressor of RLR1 (THO2) and is required for lacZ expression in yeast, placing Sub2 in the same mRNA export pathway as THO2 and suggesting THO2 links transcription to Sub2-mediated mRNP assembly/export. Dosage-dependent suppressor screen of rlr1-1 cold-sensitive phenotype, lacZ reporter assays, genetic analysis of sub2 mutants Gene Medium 12034490
2002 Null mutations in THO2 (and HPR1) impair transcription-coupled nucleotide excision repair (TCR) and, to a lesser extent, global genome repair (GGR), establishing that the THO complex affects both transcription elongation and DNA repair. UV sensitivity assays of hpr1Δ and tho2Δ yeast cells lacking GGR, molecular analysis of DNA repair using T4 endo V on the RPB2 transcribed strand Nucleic acids research Medium 12000839
2015 Missense variants in human THOC2 (a subunit of the TREX mRNA-export complex) cause X-linked intellectual disability; two variants lead to decreased stability of THOC2 protein and its TREX complex partners in patient-derived cells; structural modeling locates affected residues in RNA-binding domains of THOC2. X chromosome exome sequencing, patient-derived cell stability assays (Western blot for THOC2 and TREX partners), protein structural modeling American journal of human genetics High 26166480
2018 Additional missense THOC2 variants reduce protein stability, and splice-site variants produce C-terminally truncated THOC2 proteins; reduced THOC2 stability causes downstream destabilization of other TREX complex subunits (THOC1, THOC5, THOC6, THOC7). Functional studies in patient-derived cell lines (Western blotting for THOC2 and TREX subunit stability), analysis of splice-site variants and truncation products Human mutation High 29851191
2013 THOC2 knockdown in primary rat hippocampal neurons increased neurite extension, and knockdown in neuronal stem cells (LC1) increased their in vitro growth rate without modifying apoptosis; knockout of the THOC2 ortholog in C. elegans produced functional defects in specific sensory neurons. Thoc2 knockdown (siRNA/shRNA) in primary neurons and neuronal stem cells, C. elegans ortholog knockout with sensory neuron functional assays Journal of medical genetics Medium 23749989
2020 Reduced stability of THOC2 variant proteins has a flow-on effect on the stability of other NDD-associated THOC subunits; splicing-defective and deletion variants result in loss of small regions of the C-terminal THOC2 RNA-binding domain (RBD), establishing the C-terminal RBD as functionally important for complex integrity. Ex vivo missense variant testing, patient-derived cell line protein stability assays (Western blot for THOC2 and TREX subunits), intragenic deletion analysis Frontiers in molecular neuroscience High 32116545
2024 Compromised THOC2/TREX function (via a hypomorphic Thoc2 exon 37-38 deletion) in mice causes R-loop accumulation, DNA damage, and consequent cell death in brain development, establishing that perturbed R-loop homeostasis is a molecular mechanism underlying THOC2 syndrome. Mouse model (Thoc2Δ/Y hypomorphic deletion), R-loop accumulation assays, DNA damage markers, behavioral phenotyping (spatial learning, working memory, sensorimotor function) Nature communications High 38331934
2021 THOC2 promotes stem-like properties and radioresistance of triple-negative breast cancer cells in a THOC5-dependent manner by facilitating the nuclear export of SOX2 and NANOG transcripts; silencing THOC2 decreases SOX2 and NANOG protein expression and radiosensitizes cells. THOC2/THOC5 siRNA knockdown in TNBC cell lines, nuclear/cytoplasmic RNA fractionation, protein expression analysis (Western blot), xenograft tumor growth assays Advanced science (Weinheim, Baden-Wurttemberg, Germany) Medium 34708581
2023 Upon perturbation of mRNP biogenesis, yeast Tho2 independently (outside the THO complex) recruits the RNA exosome subunit Rrp6 to chromatin via its carboxy-terminal domain; other THO subunits are not required for this function, establishing a THO complex-independent role for Tho2 in cotranscriptional mRNP quality control. Genome-wide ChIP-seq of THO subunits (Tho2, Thp2, Hpr1, Mft1) under mRNP biogenesis perturbation (bacterial Rho helicase expression), epistasis analysis of Tho2 C-terminal domain RNA (New York, N.Y.) High 37914399
2024 Yeast Tho2 escorts the transcriptional terminator Nrd1 on chromatin; Tho2 deletion causes aberrant/arbitrary Nrd1 chromatin binding and increased Nrd1 recruitment to translation-associated aging-related genes, linking Tho2 to lifespan regulation through transcriptional control of aging genes. Genome-wide ChIP-seq of Nrd1 in tho2Δ mutants, replicative lifespan assays, genetic epistasis (hpr1Δ, tho2Δ, rrp6Δ, NRD1 overexpression), interaction assays Aging cell Medium 38769776
2023 THOC2 knockdown in GBM cells alters Bcl-x pre-mRNA splicing, increasing the pro-apoptotic Bcl-xS isoform, and reduces L1CAM expression, impairing cell adhesion and migration; these effects correlate with reduced 5-FU resistance. shRNA knockdown of THOC2 in GBM cell lines, RNA sequencing for alternative splicing variants, RT-qPCR, xenograft mouse model American journal of cancer research Medium 37424800

Source papers

Stage 0 corpus · 22 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2000 A protein complex containing Tho2, Hpr1, Mft1 and a novel protein, Thp2, connects transcription elongation with mitotic recombination in Saccharomyces cerevisiae. The EMBO journal 257 11060033
1998 A novel yeast gene, THO2, is involved in RNA pol II transcription and provides new evidence for transcriptional elongation-associated recombination. The EMBO journal 131 9707445
2015 THOC2 Mutations Implicate mRNA-Export Pathway in X-Linked Intellectual Disability. American journal of human genetics 61 26166480
2021 THOC2 and THOC5 Regulate Stemness and Radioresistance in Triple-Negative Breast Cancer. Advanced science (Weinheim, Baden-Wurttemberg, Germany) 48 34708581
2013 A de novo X;8 translocation creates a PTK2-THOC2 gene fusion with THOC2 expression knockdown in a patient with psychomotor retardation and congenital cerebellar hypoplasia. Journal of medical genetics 32 23749989
1996 Localisation of a new gene for non-specific mental retardation to Xq22-q26 (MRX35). Journal of medical genetics 30 8825049
2019 Knockdown THOC2 suppresses the proliferation and invasion of melanoma. Bioengineered 21 31680623
2018 Severe neurocognitive and growth disorders due to variation in THOC2, an essential component of nuclear mRNA export machinery. Human mutation 21 29851191
2000 RLR1 (THO2), required for expressing lacZ fusions in yeast, is conserved from yeast to humans and is a suppressor of SIN4. Gene 17 10675628
2020 Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor. Frontiers in molecular neuroscience 16 32116545
2002 Defective nucleotide excision repair in yeast hpr1 and tho2 mutants. Nucleic acids research 15 12000839
2024 Compromised transcription-mRNA export factor THOC2 causes R-loop accumulation, DNA damage and adverse neurodevelopment. Nature communications 12 38331934
2009 The putative RNA-processing protein, THO2, is a microtubule-associated protein in tobacco. Plant & cell physiology 10 19218314
2002 DEAD-box RNA helicase Sub2 is required for expression of lacZ fusions in Saccharomyces cerevisiae and is a dosage-dependent suppressor of RLR1 (THO2). Gene 6 12034490
2024 Tho2-mediated escort of Nrd1 regulates the expression of aging-related genes. Aging cell 5 38769776
2023 THOC2 expression and its impact on 5-fluorouracil resistance in glioblastoma multiforme. American journal of cancer research 5 37424800
2021 Novel Consensus Splice Site Pathogenic Variation in THOC2 Gene Leads to Recurrent Arthrogryposis Multiplex Congenita Phenotype: A Case Report. Cureus 4 34976470
2023 Tho2 is critical for the recruitment of Rrp6 to chromatin in response to perturbed mRNP biogenesis. RNA (New York, N.Y.) 2 37914399
2023 Muscular phenotype description of abnormal THOC2 splicing. Neuromuscular disorders : NMD 2 37945483
2026 Mutation in THO2, a component of THO/TREX complex, causes transcriptional gene silencing and genome-wide DNA methylation changes. The Plant journal : for cell and molecular biology 0 41604663
2025 Targeting mRNA export complex macromolecules THO subunits (Thoc2 and Thoc5) for somatic cell reprograming. International journal of biological macromolecules 0 40107550
2024 Color tunable luminescence in ThO2:Er3+,Yb3+ nanocrystals: a promising new platform for upconversion. Physical chemistry chemical physics : PCCP 0 38436395

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