Affinage

SLX9

Ribosome biogenesis protein SLX9 homolog · UniProt Q9NSI2

Length
230 aa
Mass
25.5 kDa
Annotated
2026-06-10
9 papers in source corpus 6 papers cited in narrative 6 extracted findings
Cross-family judge faithfulness: 4/4 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

SLX9 (FAM207A/C21orf70) is a pre-40S ribosomal particle component that functions in small subunit (SSU) maturation and nuclear export (PMID:21097556, PMID:17018574). It acts as a RanGTP-binding scaffold that forms a trimeric complex with the pre-40S-associated NES adaptor Rio2 and RanGTP, thereby loading the exportin Crm1 through a non-canonical, stepwise mechanism to drive 40S pre-ribosome nuclear export; a mutation that disrupts Crm1-export complex assembly blocks this export (PMID:25895666). In yeast, Slx9p additionally associates with 35S, 23S, and 20S pre-rRNA and U3 snoRNA and is required for ITS1 processing events that separate the large- and small-subunit pre-ribosomal particles (PMID:17018574), and its release from late SSU precursors is gated by assembly of the rpS0 (uS2) S0-cluster as part of an r-protein assembly checkpoint (PMID:30653518). Beyond its ribosomal role, yeast Slx9 binds G-quadruplex DNA in vitro and accumulates at G4 structures when the RecQ helicase Sgs1 is absent (PMID:31067825).

Mechanistic history

Synthesis pass · year-by-year structured walk · 6 steps
  1. 2006 Medium

    Established Slx9 as a bona fide pre-ribosome component and placed it functionally at ITS1 processing, answering what cellular process the previously uncharacterized protein participates in.

    Evidence Co-IP of pre-rRNA/U3 snoRNA, Northern blotting of processing intermediates, and synthetic lethality with rrp5 mutants in yeast

    PMID:17018574

    Open questions at the time
    • Does not define the direct molecular activity of Slx9 in cleavage
    • Conservation of the processing role in human cells not addressed
    • No structural or interaction detail with the processing machinery
  2. 2010 Medium

    Showed the human ortholog C21orf70/SLX9 is a constituent of human pre-40S particles, establishing conservation of the ribosomal association in human cells.

    Evidence Tandem affinity purification of pre-40S particles with mass spectrometry in human somatic cells

    PMID:21097556

    Open questions at the time
    • No functional follow-up on the human protein specifically
    • Does not establish a mechanism within human pre-40S maturation
  3. 2015 High

    Defined the molecular mechanism by which Slx9 promotes 40S export, resolving how the NES adaptor Rio2 is coupled to Crm1.

    Evidence In vitro reconstitution of a Slx9-Rio2-RanGTP trimeric complex, mutational analysis, and nuclear export assays

    PMID:25895666

    Open questions at the time
    • Structural basis of the scaffold interaction not determined
    • Whether the human ortholog uses the identical Crm1-loading mechanism not tested
    • Timing of Slx9 action relative to other export factors unresolved
  4. 2019 Medium

    Placed Slx9 release within a defined r-protein assembly checkpoint, clarifying when Slx9 leaves the maturing SSU particle.

    Evidence Semi-quantitative proteomics of Rio2-associated SSU precursors plus biochemical fractionation in yeast r-protein mutants

    PMID:30653518

    Open questions at the time
    • Mechanistic trigger linking S0-cluster assembly to Slx9 release not defined
    • Release inferred from mutant comparison rather than direct kinetics
  5. 2019 Medium

    Revealed a non-ribosomal activity of Slx9 as a G-quadruplex DNA binder that engages stabilized G4 structures when Sgs1 is absent.

    Evidence Yeast one-hybrid screen, in vitro G4 binding assay, and genome-wide ChIP-seq in wild-type and sgs1Δ cells

    PMID:31067825

    Open questions at the time
    • Biological consequence of G4 binding (protection vs. processing) not functionally demonstrated
    • Relationship between the ribosomal and G4-binding roles unknown
    • Whether human SLX9 binds G4 DNA not tested
  6. 2021 Low

    Reinforced the ribosome-biogenesis association and nucleolar localization of the human protein via proximity labeling.

    Evidence BioID proximity-dependent biotinylation and subcellular localization imaging in human cells

    PMID:34780483

    Open questions at the time
    • BioID proximity does not establish direct interactions or mechanism for FAM207A specifically
    • Single screen with limited functional follow-up

Open questions

Synthesis pass · forward-looking unresolved questions
  • Whether the human protein recapitulates the yeast ITS1-processing and G4-binding functions, and the structural basis of its Rio2/RanGTP/Crm1 scaffolding, remain open.
  • No structure of the Slx9-Rio2-RanGTP-Crm1 assembly
  • Human-specific functional dissection of SLX9 lacking
  • Functional significance of G4 binding in vivo undefined

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0003677 DNA binding 1 GO:0060090 molecular adaptor activity 1
Localization
GO:0005634 nucleus 1 GO:0005730 nucleolus 1
Pathway
R-HSA-8953854 Metabolism of RNA 3 R-HSA-9609507 Protein localization 1
Partners
CRM1RANRIO2RRP12RRP5
Complex memberships
pre-40S ribosomal particle

Evidence

Reading pass · 6 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2015 Slx9 is a novel RanGTP-binding protein that facilitates Crm1 recruitment to the 40S pre-ribosome-associated NES-containing adaptor Rio2. In vitro, Slx9 binds Rio2 and RanGTP, forming a trimeric complex that directly loads Crm1 via a non-canonical stepwise mechanism. A mutation in Slx9 that impairs Crm1-export complex assembly inhibits 40S pre-ribosome export, establishing Slx9 as a scaffold that optimally presents RanGTP and the NES to Crm1 to trigger 40S pre-ribosome nuclear export. In vitro binding assays, mutational analysis, nuclear export assays, co-immunoprecipitation eLife High 25895666
2010 C21orf70 (SLX9/FAM207A) was identified as a novel component of human pre-40S ribosomal particles by tandem affinity purification of pre-40S assemblies in human somatic cells. Tandem affinity purification (TAP) of pre-40S ribosomal particles combined with mass spectrometry RNA (New York, N.Y.) Medium 21097556
2006 Yeast Slx9p (Ygr081cp) is associated with 35S, 23S, and 20S pre-rRNA and U3 snoRNA (making it a bona fide pre-ribosome component), and deletion of SLX9 causes accumulation of mutually exclusive 21S and 27SA2 pre-rRNA intermediates, indicating a role in ITS1 processing events that separate the 66S and 43S pre-ribosomal particles. Synthetic lethality of slx9Δ with Rrp5p mutations blocking cleavage at site A2 or A3 places Slx9p genetically at ITS1 processing. Co-immunoprecipitation (pre-rRNA and U3 snoRNA association), Northern blotting of pre-rRNA processing intermediates, genetic epistasis (synthetic lethality with rrp5 mutants) RNA (New York, N.Y.) Medium 17018574
2019 In yeast, Slx9 binds G-quadruplex (G4) DNA structures in vitro, identified in a yeast one-hybrid screen. Genome-wide ChIP-seq shows only insignificant binding to G4 regions under normal conditions, but Slx9 binding to G4 structures is significantly increased in the absence of the RecQ helicase Sgs1, suggesting Slx9 recognizes and protects stabilized G4 structures when they are not unwound. Yeast one-hybrid screen, in vitro G4 binding assay, genome-wide ChIP-seq in wild-type and sgs1Δ cells Molecules (Basel, Switzerland) Medium 31067825
2019 In yeast, formation of the S0-cluster of ribosomal proteins around rpS0 (uS2) on late SSU precursors is required for efficient release of the nuclear export factors Rrp12 and Slx9 from SSU precursors, placing Slx9 release downstream of S0-cluster assembly as part of an r-protein assembly checkpoint during late SSU maturation. Semi-quantitative proteomics of Rio2-associated SSU precursors combined with complementary biochemical fractionation in S. cerevisiae r-protein mutants PloS one Medium 30653518
2021 FAM207A (SLX9) associates with proteins involved in ribosome biosynthesis and localizes to the nucleolus, as detected by proximity-dependent biotinylation (BioID) in human cells. BioID proximity-dependent biotinylation, subcellular localization imaging PLoS genetics Low 34780483

Source papers

Stage 0 corpus · 9 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2010 Tandem affinity purification combined with inducible shRNA expression as a tool to study the maturation of macromolecular assemblies. RNA (New York, N.Y.) 41 21097556
2015 A non-canonical mechanism for Crm1-export cargo complex assembly. eLife 35 25895666
2001 From PREDs and open reading frames to cDNA isolation: revisiting the human chromosome 21 transcription map. Genomics 34 11707072
2006 Slx9p facilitates efficient ITS1 processing of pre-rRNA in Saccharomyces cerevisiae. RNA (New York, N.Y.) 22 17018574
2021 ATRX proximal protein associations boast roles beyond histone deposition. PLoS genetics 19 34780483
2019 A Novel G-Quadruplex Binding Protein in Yeast-Slx9. Molecules (Basel, Switzerland) 15 31067825
2019 Impact of two neighbouring ribosomal protein clusters on biogenesis factor binding and assembly of yeast late small ribosomal subunit precursors. PloS one 11 30653518
2010 A new plant sex-linked gene with high sequence diversity and possible introgression of the X copy. Heredity 9 20551975
2025 FAM207A acts as a novel and potential biomarker in lung adenocarcinoma and shapes the immunesuppressive tumor microenvironment. Clinical and experimental medicine 0 40259152

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