id: P49458
gene_symbol: SRP9
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: 'SRP9 is the 9 kDa subunit of the signal recognition particle (SRP), the cytosolic ribonucleoprotein that mediates co-translational targeting of secretory and membrane proteins to the endoplasmic reticulum (ER). SRP comprises a single 7SL RNA (~300 nucleotides) and six proteins (SRP9, SRP14, SRP19, SRP54, SRP68, SRP72). SRP9 binds the SRP RNA as an obligate heterodimer with SRP14, and together with the Alu portion of the SRP RNA forms the Alu domain at one end of the particle. This Alu domain is the elongation-arrest module of SRP. When SRP binds a ribosome translating a signal sequence, the SRP9/SRP14 heterodimer reaches into the ribosomal elongation-factor binding site and transiently pauses (arrests) translation elongation, giving SRP time to deliver the ribosome-nascent chain complex to the ER membrane SRP receptor. SRP9 is an RNA-binding protein rather than a GTPase (the GTPases of the pathway are SRP54 and the SRP-receptor subunits). It functions in the cytoplasm/cytosol; SRP9/SRP14 transit the nucleolus during SRP assembly.'
alternative_products:
- name: '1'
  id: P49458-1
- name: '2'
  id: P49458-2
  sequence_note: VSP_041270
existing_annotations:
- term:
    id: GO:0006614
    label: SRP-dependent cotranslational protein targeting to membrane
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: Phylogenetic annotation of SRP9's defining biological process. As part of SRP, SRP9 (via the Alu/elongation-arrest domain) contributes to SRP-dependent co-translational targeting of proteins to the ER membrane. Conserved across the SRP9 family.
    action: ACCEPT
    reason: Core biological process; SRP9 is an SRP subunit essential to co-translational ER targeting.
    supported_by:
    - reference_id: file:human/SRP9/SRP9-uniprot.txt
      supporting_text: mediates the cotranslational targeting
- term:
    id: GO:0005786
    label: signal recognition particle, endoplasmic reticulum targeting
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: part_of
  review:
    summary: Phylogenetic annotation of SRP9 as a constitutive subunit of the signal recognition particle. Conserved and directly established.
    action: ACCEPT
    reason: Core cellular component; SRP9 is one of the six SRP protein subunits.
    supported_by:
    - reference_id: file:human/SRP9/SRP9-uniprot.txt
      supporting_text: 'consists of a 7SL RNA molecule of 300 nucleotides and six protein'
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: Electronic transfer of the cytoplasmic localization from the UniProt subcellular location. SRP functions in the cytoplasm targeting nascent chains to the ER.
    action: ACCEPT
    reason: Correct compartment; SRP acts in the cytoplasm.
    supported_by:
    - reference_id: file:human/SRP9/SRP9-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Cytoplasm.'
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  qualifier: located_in
  review:
    summary: ARBA machine-learning electronic annotation of cytosolic localization, consistent with the cytoplasmic site of SRP function.
    action: ACCEPT
    reason: Correct compartment; consistent with UniProt cytoplasm and Reactome cytosol.
    supported_by:
    - reference_id: file:human/SRP9/SRP9-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Cytoplasm.'
- term:
    id: GO:0006614
    label: SRP-dependent cotranslational protein targeting to membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: involved_in
  review:
    summary: InterPro-based electronic assignment of the core SRP-dependent co-translational targeting process.
    action: ACCEPT
    reason: Correct core process; redundant with IBA/NAS evidence.
    supported_by:
    - reference_id: file:human/SRP9/SRP9-uniprot.txt
      supporting_text: mediates the cotranslational targeting
- term:
    id: GO:0008312
    label: 7S RNA binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: InterPro-based annotation of SRP RNA (7S/7SL) binding. SRP9 binds the SRP 7SL RNA as part of the SRP9/SRP14 Alu-domain heterodimer; this RNA-binding is its core molecular function.
    action: ACCEPT
    reason: Core molecular function; SRP9 (with SRP14) binds the Alu portion of the SRP RNA.
    supported_by:
    - reference_id: file:human/SRP9/SRP9-uniprot.txt
      supporting_text: The complex of SRP9 and SRP14 is required for SRP
- term:
    id: GO:0045900
    label: negative regulation of translational elongation
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: involved_in
  review:
    summary: InterPro-based annotation of the elongation-arrest function. The SRP9/SRP14 Alu domain transiently arrests translation elongation by reaching into the ribosomal elongation-factor binding site. This is the defining SRP9-specific contribution to SRP function.
    action: ACCEPT
    reason: Core biological process; SRP9 is part of the Alu/elongation-arrest domain that negatively regulates elongation.
    supported_by:
    - reference_id: PMID:34208095
      supporting_text: SRP9 and SRP14 function in elongation arrest
- term:
    id: GO:0048500
    label: signal recognition particle
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: part_of
  review:
    summary: InterPro-based annotation of SRP complex membership (general SRP term). SRP9 is a constitutive subunit.
    action: ACCEPT
    reason: Core cellular component; redundant with the more specific GO:0005786.
    supported_by:
    - reference_id: file:human/SRP9/SRP9-uniprot.txt
      supporting_text: 'Component of the signal recognition particle (SRP) complex'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:25910212
  qualifier: enables
  review:
    summary: High-throughput interactome screen; the captured partner (ACTN2) is unrelated to SRP9's function. Bare protein binding is uninformative.
    action: KEEP_AS_NON_CORE
    reason: Incidental high-throughput interaction; bare protein binding is uninformative.
    supported_by:
    - reference_id: file:human/SRP9/SRP9-uniprot.txt
      supporting_text: 'P49458; P35609: ACTN2'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:28514442
  qualifier: enables
  review:
    summary: Human interactome study capturing the functionally central SRP9-SRP14 (P37108) Alu-heterodimer interaction. Biologically meaningful but the bare protein binding term is uninformative.
    action: KEEP_AS_NON_CORE
    reason: Records the real SRP14 heterodimer interaction, but bare protein binding is uninformative; the informative MF is captured by GO:0008312 and complex membership by GO:0005786.
    supported_by:
    - reference_id: file:human/SRP9/SRP9-uniprot.txt
      supporting_text: 'P49458; P37108: SRP14'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:30021884
  qualifier: enables
  review:
    summary: Crosslinking-MS interactome capturing the SRP9-SRP14 (P37108) interaction. Bare protein binding is uninformative.
    action: KEEP_AS_NON_CORE
    reason: Records the real SRP14 interaction; bare protein binding is uninformative.
    supported_by:
    - reference_id: file:human/SRP9/SRP9-uniprot.txt
      supporting_text: 'P49458; P37108: SRP14'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:32296183
  qualifier: enables
  review:
    summary: HuRI binary interactome capturing the SRP9-SRP14 (P37108) interaction. Bare protein binding is uninformative.
    action: KEEP_AS_NON_CORE
    reason: Records the real SRP14 interaction; bare protein binding is uninformative.
    supported_by:
    - reference_id: file:human/SRP9/SRP9-uniprot.txt
      supporting_text: 'P49458; P37108: SRP14'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:32814053
  qualifier: enables
  review:
    summary: Neurodegenerative-disease interactome mapping; captured partners (CDHR3, DPP9, RYBP) are unrelated to SRP9's function. Bare protein binding is uninformative.
    action: KEEP_AS_NON_CORE
    reason: Incidental high-throughput interactions; bare protein binding is uninformative.
    supported_by:
    - reference_id: file:human/SRP9/SRP9-uniprot.txt
      supporting_text: 'P49458; Q6ZTQ4: CDHR3'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:33961781
  qualifier: enables
  review:
    summary: Proteome-scale interactome capturing the SRP9-SRP14 (P37108) interaction. Bare protein binding is uninformative.
    action: KEEP_AS_NON_CORE
    reason: Records the real SRP14 interaction; bare protein binding is uninformative.
    supported_by:
    - reference_id: file:human/SRP9/SRP9-uniprot.txt
      supporting_text: 'P49458; P37108: SRP14'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:35271311
  qualifier: enables
  review:
    summary: OpenCell endogenous-tagging interactome capturing the SRP9-SRP14 (P37108) interaction. Bare protein binding is uninformative.
    action: KEEP_AS_NON_CORE
    reason: Records the real SRP14 interaction; bare protein binding is uninformative.
    supported_by:
    - reference_id: file:human/SRP9/SRP9-uniprot.txt
      supporting_text: 'P49458; P37108: SRP14'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:40205054
  qualifier: enables
  review:
    summary: Multimodal cell map capturing the SRP9-SRP14 (P37108) interaction. Bare protein binding is uninformative.
    action: KEEP_AS_NON_CORE
    reason: Records the real SRP14 interaction; bare protein binding is uninformative.
    supported_by:
    - reference_id: file:human/SRP9/SRP9-uniprot.txt
      supporting_text: 'P49458; P37108: SRP14'
- term:
    id: GO:0005786
    label: signal recognition particle, endoplasmic reticulum targeting
  evidence_type: NAS
  original_reference_id: PMID:34208095
  qualifier: part_of
  review:
    summary: ComplexPortal NAS assertion of SRP complex membership, from the SRP review describing the SRP9/SRP14 Alu domain.
    action: ACCEPT
    reason: Core cellular component; SRP9 is an SRP subunit.
    supported_by:
    - reference_id: PMID:34208095
      supporting_text: 'Alu domain'
- term:
    id: GO:0006617
    label: SRP-dependent cotranslational protein targeting to membrane, signal sequence recognition
  evidence_type: NAS
  original_reference_id: PMID:34208095
  qualifier: involved_in
  review:
    summary: ComplexPortal NAS (complex-level) annotation of signal-sequence recognition. Signal-sequence recognition is performed by the SRP54 subunit of the SRP, not directly by SRP9, whose specific role is elongation arrest within the Alu domain. The term applies at the SRP complex level of which SRP9 is part.
    action: KEEP_AS_NON_CORE
    reason: Complex-level NAS annotation; signal-sequence recognition is the SRP54 function, while SRP9's direct contribution is elongation arrest.
    supported_by:
    - reference_id: PMID:34208095
      supporting_text: signal sequence
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:24965446
  qualifier: enables
  review:
    summary: SRP9 co-purifies with the pestivirus Npro ribonucleoprotein complex; an incidental ribosomal/RNP capture from a viral interactome study. Bare protein binding is uninformative.
    action: KEEP_AS_NON_CORE
    reason: Incidental viral RNP co-purification; bare protein binding is uninformative.
    supported_by:
    - reference_id: PMID:24965446
      supporting_text: components of the ribonucleoprotein complex
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-1799332
  qualifier: located_in
  review:
    summary: Reactome curation of cytosolic localization, consistent with SRP's cytoplasmic site of action.
    action: ACCEPT
    reason: Correct compartment; redundant with UniProt cytoplasm.
    supported_by:
    - reference_id: file:human/SRP9/SRP9-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Cytoplasm.'
- term:
    id: GO:0005786
    label: signal recognition particle, endoplasmic reticulum targeting
  evidence_type: NAS
  original_reference_id: PMID:17154533
  qualifier: part_of
  review:
    summary: NAS assertion of SRP complex membership from a study on compartmentalized SRP assembly.
    action: ACCEPT
    reason: Core cellular component; SRP9 is an SRP subunit.
    supported_by:
    - reference_id: PMID:17154533
      supporting_text: Compartmentalization directs assembly of the signal recognition particle
- term:
    id: GO:0003723
    label: RNA binding
  evidence_type: TAS
  original_reference_id: PMID:7730321
  qualifier: enables
  review:
    summary: SRP9 (with SRP14) is the Alu RNA-binding protein that binds the Alu region of 7SL RNA. RNA binding is correct but is the general parent of the more specific 7S RNA binding.
    action: ACCEPT
    reason: Correct molecular function; the more specific GO:0008312 (7S RNA binding) better captures SRP9's role.
    supported_by:
    - reference_id: PMID:7730321
      supporting_text: regulates translational elongation of
- term:
    id: GO:0005047
    label: signal recognition particle binding
  evidence_type: TAS
  original_reference_id: PMID:7730321
  qualifier: enables
  review:
    summary: Annotation of SRP9 binding the signal recognition particle. SRP9 is itself a constitutive subunit of SRP rather than an external SRP-binding factor, so this is redundant with its part_of SRP membership.
    action: KEEP_AS_NON_CORE
    reason: SRP9 is part of SRP (captured by GO:0005786); describing it as SRP-binding is redundant and not the informative core MF.
    supported_by:
    - reference_id: file:human/SRP9/SRP9-uniprot.txt
      supporting_text: 'consists of a 7SL RNA molecule of 300 nucleotides and six protein'
- term:
    id: GO:0005785
    label: signal recognition particle receptor complex
  evidence_type: TAS
  original_reference_id: PMID:7730321
  qualifier: part_of
  review:
    summary: SRP9 is annotated as part of the signal recognition particle receptor (SR) complex. This is incorrect; PMID:7730321 characterizes SRP9 as a component of the SRP (the Alu RNA-binding protein), not of the SRP receptor (SRalpha/SRbeta) complex. This appears to be an SRP-versus-SRP-receptor curation confusion.
    action: MARK_AS_OVER_ANNOTATED
    reason: SRP9 is a subunit of SRP, not of the SRP receptor complex; the cited paper concerns SRP9 within SRP, so this CC is a mis-/over-annotation.
    supported_by:
    - reference_id: PMID:7730321
      supporting_text: regulates translational elongation of
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:0000117
  title: Electronic Gene Ontology annotations created by ARBA machine learning models
  findings: []
- id: PMID:7730321
  title: Human signal recognition particle (SRP) Alu-associated protein also binds Alu interspersed repeat sequence RNAs. Characterization of human SRP9.
  findings:
  - statement: SRP9 with SRP14 (SRP9/14) is the Alu RNA-binding protein that binds the Alu region of 7SL RNA and regulates translational elongation of ribosomes engaged by SRP.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Characterizes human SRP9 as the Alu RNA-binding protein within SRP; concerns SRP (not the SRP receptor).
- id: PMID:17154533
  title: Compartmentalization directs assembly of the signal recognition particle.
  findings:
  - statement: Describes compartmentalized (nucleolar/cytoplasmic) assembly of SRP, of which SRP9 is a subunit.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Source of an SRP complex-membership NAS annotation.
- id: PMID:24965446
  title: Host factors that interact with the pestivirus N-terminal protease, Npro, are components of the ribonucleoprotein complex.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Viral RNP interactome; SRP9 co-purifies incidentally as a ribosomal/RNP component.
- id: PMID:25910212
  title: Widespread macromolecular interaction perturbations in human genetic disorders.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: High-throughput interactome; incidental ACTN2 partner, bare protein binding.
- id: PMID:28514442
  title: Architecture of the human interactome defines protein communities and disease networks.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Captures the functionally central SRP9-SRP14 interaction; bare protein binding term.
- id: PMID:30021884
  title: Histone Interaction Landscapes Visualized by Crosslinking Mass Spectrometry in Intact Cell Nuclei.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Crosslinking-MS; captures SRP14 interaction, bare protein binding.
- id: PMID:32296183
  title: A reference map of the human binary protein interactome.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: HuRI Y2H; captures SRP9-SRP14 interaction, bare protein binding.
- id: PMID:32814053
  title: Interactome Mapping Provides a Network of Neurodegenerative Disease Proteins and Uncovers Widespread Protein Aggregation in Affected Brains.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: High-throughput interactome; incidental partners, bare protein binding.
- id: PMID:33961781
  title: Dual proteome-scale networks reveal cell-specific remodeling of the human interactome.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Captures the SRP9-SRP14 interaction; bare protein binding term.
- id: PMID:34208095
  title: 'SRPassing Co-translational Targeting: The Role of the Signal Recognition Particle in Protein Targeting and mRNA Protection.'
  findings:
  - statement: SRP9 and SRP14 form the Alu domain of SRP and function in elongation arrest, positioning near the ribosomal elongation-factor binding site to pause translation; signal-sequence recognition is performed by SRP54.
    reference_section_type: OTHER
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Authoritative SRP review describing SRP9/14 Alu-domain elongation arrest; full text available.
- id: PMID:35271311
  title: 'OpenCell: Endogenous tagging for the cartography of human cellular organization.'
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Endogenous-tagging interactome; captures SRP9-SRP14 interaction, bare protein binding.
- id: PMID:40205054
  title: Multimodal cell maps as a foundation for structural and functional genomics.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Cell map; captures SRP9-SRP14 interaction, bare protein binding.
- id: Reactome:R-HSA-1799332
  title: 'Reactome: Nascent polypeptide:mRNA:ribosome complex binds signal recognition particle (SRP)'
  findings: []
- id: PMID:26585389
  title: Retrotransposition and Crystal Structure of an Alu RNP in the Ribosome-Stalling Conformation.
  findings:
  - statement: 2.0 A crystal structure of the human Alu RNP (SRP9/14 bound to Alu RNA) in the ribosome-stalling conformation; SRP9/14 clamps the Alu RNA and docks at the ribosomal elongation-factor binding site, and mutations weakening the SRP9/14-RNA interface abolish Alu retrotransposition.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: PubMed-verified (Ahl et al., Mol Cell 2015, PDB 5AOX). Structural basis of the SRP9/14 Alu-domain RNA clamp and its ribosome-stalling geometry; also links SRP9/14 to Alu retrotransposition.
- id: PMID:37156570
  title: Nuclear SRP9/SRP14 heterodimer transcriptionally regulates 7SL and BC200 RNA expression.
  findings:
  - statement: SRP9/14 localizes substantially in the nucleus; siRNA knockdown selectively reduces the Alu-like Pol III transcripts 7SL (RN7SL1) and BC200 (BCYRN1) by decreasing Pol III occupancy at these loci rather than altering RNA stability, defining a noncanonical nuclear transcriptional role for SRP9/14.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: PubMed-verified (Gussakovsky et al., RNA 2023). Noncanonical nuclear role of the SRP9/14 heterodimer; not the core SRP/elongation-arrest function.
- id: PMID:37309897
  title: Alu RNA fold links splicing with signal recognition particle proteins.
  findings:
  - statement: SRP9/14 binds compact (closed) Alu RNA conformations and modulates inclusion of Alu-derived exons, with RNA structure (closed vs open Alu fold) predicting exon inclusion; demonstrates a noncanonical SRP9/14 role in pre-mRNA splicing regulation.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: PubMed-verified (Borovska et al., Nucleic Acids Res 2023). Noncanonical Alu-exon splicing-regulation role of SRP9/14; distinct from the core SRP function.
- id: PMID:38858088
  title: The nucleolar phase of signal recognition particle assembly.
  findings:
  - statement: SRP proteins (including SRP9/14) associate with many nucleolar and ribosome-biogenesis factors; GFP-SRP9 appears mostly nuclear with faint cytoplasmic staining, and nucleolar integrity is required for proper SRP protein localization, supporting a nucleolar phase of SRP assembly.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: PubMed-verified (Issa et al., Life Sci Alliance 2024). Supports a nucleolar SRP-assembly compartment and nuclear localization of SRP9 during biogenesis.
- id: PMID:39563162
  title: The role of SRP9/SRP14 in regulating Alu RNA.
  findings:
  - statement: Reviews SRP9/14 regulation of Alu-family RNAs (maturation, trafficking, splicing, retrotransposition, transcription); primate SRP9/14 is present at ~20-fold molar excess over assembled SRP and binds 7SL with sub-nanomolar affinity, enabling extensive extra-canonical Alu-RNA regulation.
    reference_section_type: OTHER
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: PubMed-verified (Gussakovsky et al., RNA Biol 2024). Synthesis of canonical and noncanonical SRP9/14 functions.
- id: PMID:38847231
  title: 'Significance of signal recognition particle 9 nuclear translocation: implications for pancreatic cancer prognosis and functionality.'
  findings:
  - statement: In resected pancreatic cancer, higher SRP9 nuclear staining is associated with improved recurrence-free survival; SRP9 nuclear translocation is modulated by amino-acid/nutrient status.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: PubMed-verified (Sato et al., Int J Oncol 2024). Biomarker/association-level finding; not core SRP9 molecular function.
- id: file:human/SRP9/SRP9-uniprot.txt
  title: UniProt entry P49458 (SRP9_HUMAN), Signal recognition particle 9 kDa protein
  findings:
  - statement: SRP9 is a subunit of the SRP ribonucleoprotein (7SL RNA + six proteins); with SRP14 and the Alu portion of the SRP RNA it forms the elongation-arrest domain; binds RNA as the SRP9/SRP14 heterodimer; cytoplasmic.
    reference_section_type: OTHER
core_functions:
- description: RNA-binding subunit that, as an obligate heterodimer with SRP14, binds the Alu portion of the SRP 7SL RNA to form the Alu (elongation-arrest) domain of the signal recognition particle.
  molecular_function:
    id: GO:0008312
    label: 7S RNA binding
  in_complex:
    id: GO:0005786
    label: signal recognition particle, endoplasmic reticulum targeting
  supported_by:
  - reference_id: file:human/SRP9/SRP9-uniprot.txt
    supporting_text: The complex of SRP9 and SRP14 is required for SRP
  - reference_id: PMID:34208095
    supporting_text: SRP9 and SRP14 function in elongation arrest
  - reference_id: PMID:26585389
    supporting_text: >-
      We defined a minimal Alu RNA sufficient for effective retrotransposition and determined
      a high-resolution structure of its complex with the SRP9/14 proteins.
- description: Part of the SRP Alu domain that transiently arrests translation elongation at the ribosomal elongation-factor site, pausing the nascent chain while SRP-dependent co-translational targeting delivers the ribosome to the ER membrane.
  molecular_function:
    id: GO:0008312
    label: 7S RNA binding
  in_complex:
    id: GO:0005786
    label: signal recognition particle, endoplasmic reticulum targeting
  supported_by:
  - reference_id: PMID:34208095
    supporting_text: SRP9 and SRP14 function in elongation arrest
  - reference_id: PMID:26585389
    supporting_text: >-
      The RNA adopts a compact, closed conformation that matches the envelope of the SRP Alu
      domain in the ribosomal translation elongation factor-binding site.
  directly_involved_in:
  - id: GO:0045900
    label: negative regulation of translational elongation
  - id: GO:0006614
    label: SRP-dependent cotranslational protein targeting to membrane
proposed_new_terms: []
suggested_questions:
- question: How strictly required is SRP9/SRP14-mediated elongation arrest for productive ER targeting in mammalian cells, given that some substrates may be targeted without efficient arrest?
- question: Do the Alu-RNA-binding activities of SRP9/SRP14 toward Alu-derived transcripts (scAlu/scB1) have any regulatory role distinct from canonical SRP function?
suggested_experiments:
- description: Reconstitute SRP with wild-type versus RNA-binding-deficient SRP9 to quantify the contribution of the SRP9/SRP14 Alu domain to elongation arrest and targeting efficiency on defined nascent-chain substrates.
- description: Use selective ribosome profiling in cells depleted of SRP9 to measure genome-wide effects on co-translational ER targeting and elongation pausing of signal-sequence-bearing mRNAs.