Affinage

NXT1

NTF2-related export protein 1 · UniProt Q9UKK6

Length
140 aa
Mass
15.8 kDa
Annotated
2026-06-10
13 papers in source corpus 10 papers cited in narrative 10 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

NXT1 (p15) is an NTF2-related protein that functions as an essential heterodimeric cofactor for nuclear RNA export, acting principally through the TAP/NXF1 export receptor (PMID:11739738, PMID:11259602). By binding the NTF2-like domain of TAP/NXF1, NXT1 enhances the affinity of the TAP-RNA complex for nuclear pore complex nucleoporins, reconstituting a TAP/NXT1/nucleoporin (e.g. p62) ternary export complex; without NXT1, TAP cannot effectively engage the NPC and mRNA export is severely attenuated, with NXT1 depletion causing nuclear accumulation of poly(A)+ RNA (PMID:11739738, PMID:11579093). Structural work shows that the NXF1:NXT1 complex dimerizes into a 2-fold symmetric platform that recognizes CTE RNA stem-loops, and that NXT1 binding directly creates nucleoporin-binding pockets at the heterodimer interface, establishing NXT1 as a switch controlling the NPC-interaction state of NXF receptors (PMID:25628361, PMID:22123199). Beyond the NXF1 pathway, NXT1 stimulates export of multiple RNA classes (mRNA, U1 snRNA, tRNA) in a manner dependent on its RanGTP-binding activity, and it binds CRM1 directly to mediate the terminal release step of CRM1-dependent export (PMID:11149927, PMID:10848583). NXT1 is co-opted by specific regulatory and viral programs: it is required for ERK1/Tpl2-controlled export of TNF-alpha mRNA via the TAP-NXT1 complex (PMID:18048358), and it forms a trimeric complex with influenza A nucleoprotein and CRM1 to promote viral NP/vRNA export (PMID:27483302). In Drosophila spermatocytes Nxt1 additionally supports tMAC-dependent transcription of testis-specific genes, a role distinct from export of already-transcribed RNA (PMID:23754955).

Mechanistic history

Synthesis pass · year-by-year structured walk · 10 steps
  1. 2000 High

    Established NXT1 as a general RNA export factor whose activity depends on RanGTP binding, broadening it beyond a single export pathway.

    Evidence Permeabilized HeLa cell in vitro export assay with U1 snRNA, tRNA and mRNA substrates and RanGTP-binding-deficient NXT1 mutants

    PMID:10848583

    Open questions at the time
    • Does not resolve which export receptor mediates each substrate
    • Mechanism of RanGTP coupling to export not defined at atomic resolution
  2. 2001 High

    Defined NXT1's role in the terminal step of CRM1-dependent protein export, showing it acts downstream of cargo translocation at the cytoplasmic NPC face.

    Evidence Direct NXT1-CRM1 binding with RanGTP sensitivity, NXT1 mutagenesis, and permeabilized-cell reconstitution of Rev reporter release with recombinant CRM1 and Ran

    PMID:11149927

    Open questions at the time
    • Structural basis of the NXT1-CRM1 interaction not determined
    • How NXT1 triggers cargo release mechanistically unresolved
  3. 2001 High

    Showed NXT1 is required for TAP-dependent, CRM1-independent export of intron-containing RNA and that its co-expression dramatically enhances TAP export activity, distinguishing the two pathways.

    Evidence Dominant-negative Rev fusion complementation, NXT1 cotransfection, leptomycin B and DeltaCAN nucleoporin inhibition, and TAP domain mutagenesis in mammalian cells

    PMID:11259602

    Open questions at the time
    • Did not biochemically reconstitute the ternary complex
    • Quantitative contribution of NXT1 to nucleoporin affinity not measured
  4. 2001 High

    Provided the biochemical mechanism: NXT1 regulates the affinity of the TAP-RNA complex for nucleoporins, reconstituting a TAP-NXT1-p62 ternary complex from recombinant proteins.

    Evidence In vitro nucleoporin binding with recombinant proteins, TAP domain mutagenesis, and in vivo intron-containing viral mRNA export reporter

    PMID:11579093

    Open questions at the time
    • Stoichiometry and structural arrangement of the ternary complex not resolved at this stage
  5. 2002 High

    Integrated the model in vivo, demonstrating that NXT1 binding is required for TAP to engage nucleoporins and shuttle, and that NXT1 loss blocks bulk mRNA export.

    Evidence Co-IP and in vitro binding in human cells, RNAi knockdown of Drosophila NXT1 with poly(A)+ RNA nuclear accumulation, dominant-negative and mutant analysis

    PMID:11739738

    Open questions at the time
    • Does not address selectivity among different mRNA classes
    • Role in steps beyond NPC docking not defined
  6. 2007 Medium

    Linked NXT1 to signal-regulated gene expression by placing the TAP-NXT1 complex downstream of the Tpl2-ERK1 pathway for selective TNF-alpha mRNA export.

    Evidence Dominant-negative ERK1/ERK2 and TAP-NXT1 disruption with TNF-alpha mRNA export readout, plus AU-rich element dependence

    PMID:18048358

    Open questions at the time
    • Pathway placement of NXT1 inferred indirectly
    • Direct molecular link between ERK1 signaling and NXT1 not established
  7. 2011 High

    Provided structural proof that NXT1 binding directly creates a nucleoporin-binding pocket at the NXF/NXT heterodimer interface, defining NXT1 as a regulator of NXF nucleoporin function.

    Evidence X-ray crystallography of C. elegans NXF2:NXT1, mutagenesis of nucleoporin-binding pockets, and nuclear envelope colocalization assays

    PMID:22123199

    Open questions at the time
    • Used NXF2 paralog in C. elegans rather than human NXF1
    • Functional consequence of the putative phosphoregulation site untested
  8. 2013 Medium

    Revealed a tissue-specific transcriptional role distinct from export, showing Nxt1 supports tMAC-dependent transcription of testis-specific genes in Drosophila spermatocytes.

    Evidence Partial loss-of-function Drosophila genetics with tMAC-dependent vs -independent promoter reporters and RNA accumulation analysis

    PMID:23754955

    Open questions at the time
    • Molecular mechanism linking Nxt1 to transcription unresolved
    • Whether this role is conserved in mammals unknown
  9. 2015 High

    Defined the structural architecture of the NXF1:NXT1 complex, showing it dimerizes into a symmetric platform that recognizes CTE RNA and promotes its export.

    Evidence 3.4 Å X-ray crystallography of NXF1 (RRM-LRR-NTF2L) with NXT1 plus biochemical binding and cellular export assays

    PMID:25628361

    Open questions at the time
    • Resolution limits atomic detail
    • How the dimer engages cellular mRNAs beyond CTE RNA not shown
  10. 2016 Medium

    Demonstrated viral exploitation of NXT1, which binds influenza A nucleoprotein and bridges it to CRM1 to drive nuclear export of viral RNP.

    Evidence Pull-down domain mapping, co-IP of an NXT1-NP-CRM1 trimeric complex, and NXT1 knockdown/overexpression with viral replication and NP localization readouts

    PMID:27483302

    Open questions at the time
    • Single lab without structural validation
    • Whether NXT1-NP binding uses the same surfaces as NXF1 binding unknown

Open questions

Synthesis pass · forward-looking unresolved questions
  • How NXT1 toggles between the NXF1/mRNA and CRM1 export pathways and whether its transcriptional role in spermatogenesis is conserved and mechanistically defined remains open.
  • No structure of the human NXT1-CRM1 interaction
  • Mechanism of NXT1's tMAC-dependent transcriptional role undefined
  • Determinants of substrate selectivity across export pathways unresolved

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060090 molecular adaptor activity 3 GO:0098772 molecular function regulator activity 3 GO:0003723 RNA binding 1
Localization
GO:0005634 nucleus 1 GO:0005635 nuclear envelope 1
Pathway
R-HSA-8953854 Metabolism of RNA 3 R-HSA-9609507 Protein localization 2
Partners
CRM1NUP62NXF1NXF2RAN
Complex memberships
NXT1-NP-CRM1 complexTAP/NXF1-NXT1 heterodimerTAP/NXT1/nucleoporin ternary export complex

Evidence

Reading pass · 10 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2002 NXT1 forms a heterodimer with TAP/NXF1, and this heterodimer enhances TAP binding to nucleoporins both in vitro and in vivo, forming a TAP/NXT1/nucleoporin ternary complex. In the absence of NXT1 binding, TAP cannot effectively interact with nuclear pore complex components, severely attenuating TAP nucleocytoplasmic shuttling and mRNA nuclear export. RNAi knockdown of Drosophila NXT1 causes nuclear accumulation of poly(A)+ RNA in insect cells. Co-immunoprecipitation, in vitro binding assays, RNA interference (RNAi) knockdown with poly(A)+ RNA localization readout, dominant-negative and mutant analysis in human and Drosophila cells Molecular and cellular biology High 11739738
2001 NXT1 (p15) is a crucial cellular cofactor for TAP-dependent nuclear export of intron-containing RNA. The domain of TAP necessary for export requires both the NXT1-interacting region and the nucleoporin-interacting region. TAP-mediated export is CRM1-independent but sensitive to a dominant-negative CAN/Nup214 FG-repeat fragment, and NXT1 co-expression dramatically enhances chimeric TAP export activity. Dominant-negative Rev fusion protein complementation assay, cotransfection with NXT1 expression vector, leptomycin B inhibition, dominant-negative nucleoporin (DeltaCAN) inhibition, mutational analysis of TAP domains Molecular and cellular biology High 11259602
2001 NXT1 stimulates binding of a TAP-RNA complex to nucleoporins in vitro (including reconstitution of TAP-NXT1-p62 ternary complex from recombinant proteins), and mutational analysis shows that NXT1-dependent nucleoporin interactions are necessary for nuclear export of intron-containing viral mRNA in vivo. NXT1 functions to regulate the affinity of the TAP-RNA complex for nucleoporins within the nuclear pore complex. In vitro nucleoporin binding assay with recombinant proteins, mutational analysis of TAP domains, in vivo nuclear export assay with intron-containing viral mRNA reporter The Journal of biological chemistry High 11579093
2001 NXT1 binds directly to CRM1, and this interaction is sensitive to Ran-GTP. Mutations in NXT1 that reduce CRM1 binding inhibit NXT1 activity in nuclear export assays. NXT1 is required for the terminal step of CRM1-mediated export: recombinant CRM1 and Ran reconstitute translocation of a Rev reporter from nucleolus to cytoplasmic face of the NPC, but the final release step requires NXT1. Direct binding assays (NXT1-CRM1 interaction), Ran-GTP sensitivity assay, NXT1 mutational analysis, permeabilized-cell nuclear export reconstitution assay with recombinant CRM1 and Ran The Journal of cell biology High 11149927
2000 NXT1 strongly stimulates nuclear export of U1 snRNA, tRNA, and mRNA in a permeabilized HeLa cell in vitro export assay, and this stimulatory activity depends on NXT1's ability to bind RanGTP, establishing NXT1 as a general RNA export factor acting on both CRM1-dependent and CRM1-independent pathways. Permeabilized HeLa cell in vitro RNA export assay, RanGTP binding assay, NXT1 mutants deficient in RanGTP binding Molecular and cellular biology High 10848583
2015 Crystal structure (3.4 Å) of the first three domains of human NXF1 (RRM, LRR, NTF2-like) together with NXT1 revealed a domain-swapped dimer with two copies of the NXF1:NXT1 complex forming a 2-fold symmetric platform. Linkers between the NXF1 LRR and NTF2-like domains interact with NXT1. This symmetric platform facilitates recognition of the CTE RNA stem-loop from SRV-1 and promotes its nuclear export. X-ray crystallography (3.4 Å), biochemical binding assays, cellular nuclear export assays Nucleic acids research High 25628361
2007 Nuclear export of TNF-alpha mRNA requires the interaction between TAP and NXT1 (as shown by dominant-negative approaches), as well as the TNF-alpha AU-rich element. ERK1 (but not ERK2) specifically controls TNF-alpha mRNA nuclear export through the Tpl2-ERK pathway, and this control operates through the TAP-NXT1 complex. Dominant-negative ERK1/ERK2 expression, TAP-NXT1 interaction disruption, TNF-alpha mRNA nuclear export assay The Journal of biological chemistry Medium 18048358
2016 NXT1 binds directly to influenza A nucleoprotein (NP) at its C-terminal region, and forms a trimeric NXT1-NP-CRM1 complex. NXT1 overexpression promotes CRM1-dependent nuclear export of NP, while NXT1 knockdown reduces viral replication kinetics and causes nuclear accumulation of viral RNA and NP. Pull-down assay (NXT1-NP interaction, C-terminal NP domain mapping), co-immunoprecipitation of NXT1/NP/CRM1 complex, NXT1 knockdown with viral replication and NP localization readouts, NXT1 overexpression nuclear export assay Viruses Medium 27483302
2013 In Drosophila primary spermatocytes, Nxt1 is required for the accumulation of testis-specific mRNAs that depend on the tMAC transcription complex; loss of Nxt1 reduces transcription from tMAC-dependent promoters rather than impairing export of already-transcribed RNA, linking Nxt1 to a tissue-specific transcriptional regulatory role. Intronless transcripts are more sensitive to Nxt1 loss than intron-containing transcripts. Partial loss-of-function Drosophila genetics, reporter gene assays with tMAC-dependent vs. tMAC-independent promoters, RNA accumulation analysis PLoS genetics Medium 23754955
2011 Crystal structure of C. elegans NXF2 bound to ceNXT1 identified contacts crucial for NXF/NXT heterodimer stability and specificity, including a probable phosphoregulation site. The ceNXF2 NTF2 domain has at least two nucleoporin binding pockets required for nuclear envelope colocalization; one pocket is formed at the NXF2/NXT1 heterodimer interface, demonstrating that NXT1 binding directly regulates NXF nucleoporin-binding function. X-ray crystallography of ceNXF2:ceNXT1 complex, mutational analysis of nucleoporin binding pockets, nuclear envelope colocalization assay Journal of molecular biology High 22123199

Source papers

Stage 0 corpus · 13 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2002 Formation of Tap/NXT1 heterodimers activates Tap-dependent nuclear mRNA export by enhancing recruitment to nuclear pore complexes. Molecular and cellular biology 98 11739738
2001 NXT1 (p15) is a crucial cellular cofactor in TAP-dependent export of intron-containing RNA in mammalian cells. Molecular and cellular biology 83 11259602
2015 The principal mRNA nuclear export factor NXF1:NXT1 forms a symmetric binding platform that facilitates export of retroviral CTE-RNA. Nucleic acids research 50 25628361
2001 RNA export mediated by tap involves NXT1-dependent interactions with the nuclear pore complex. The Journal of biological chemistry 49 11579093
2001 NXT1 is necessary for the terminal step of Crm1-mediated nuclear export. The Journal of cell biology 45 11149927
2000 RanGTP-binding protein NXT1 facilitates nuclear export of different classes of RNA in vitro. Molecular and cellular biology 36 10848583
2016 NXT1, a Novel Influenza A NP Binding Protein, Promotes the Nuclear Export of NP via a CRM1-Dependent Pathway. Viruses 22 27483302
2007 Extracellular signal-regulated kinase regulation of tumor necrosis factor-alpha mRNA nucleocytoplasmic transport requires TAP-NxT1 binding and the AU-rich element. The Journal of biological chemistry 19 18048358
2011 The structure of the NXF2/NXT1 heterodimeric complex reveals the combined specificity and versatility of the NTF2-like fold. Journal of molecular biology 18 22123199
2013 The RNA export factor, Nxt1, is required for tissue specific transcriptional regulation. PLoS genetics 16 23754955
2021 Roles for RNA export factor, Nxt1, in ensuring muscle integrity and normal RNA expression in Drosophila. G3 (Bethesda, Md.) 4 33561245
2023 Mutations in the NXF-1:NXT-1 mRNA export complex affect gene-expression driven by the hsp-16.41 promoter. microPublication biology 2 37583452
2022 Genetic characterization of nuclear export factor NXT1 and its paralog NXT2 in primates and murine rodents. Zoology (Jena, Germany) 1 35219094

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