module: dmel_srp_cotranslational_targeting
title: SRP-dependent cotranslational targeting in Drosophila melanogaster
label: SRP-dependent cotranslational targeting
module_type: BIOLOGICAL_PROCESS
description: >-
  The signal recognition particle (SRP) recognizes signal sequences and
  transmembrane segments as they emerge from the ribosome, slows elongation
  and delivers the ribosome-nascent chain complex to the SRP receptor on the
  endoplasmic reticulum membrane. SRP is a ribonucleoprotein built on the 7SL
  RNA. Its Alu domain (SRP9 and SRP14) arrests elongation, and its S domain
  (SRP19, SRP54, SRP68 and SRP72) binds the signal sequence through the
  methionine-rich domain of the GTPase SRP54. The receptor is a heterodimer of
  the GTPases SRalpha and SRbeta. GTP-dependent interaction of SRP54 with
  SRalpha transfers the nascent chain to the Sec61 translocon, and reciprocal
  GTP hydrolysis releases SRP from its receptor.
summary: >-
  SRP ribonucleoprotein and its ER receptor that target ribosome-nascent chain
  complexes to the Sec61 translocon.
concepts:
  - {id: GO:0006614, label: SRP-dependent cotranslational protein targeting to membrane}
cellular_components:
  - {id: GO:0005789, label: endoplasmic reticulum membrane}
notes: >-
  Boundary. The module ends at handover to the translocon; Sec61 and its
  partners are a separate module (dmel_sec61_translocon). Drosophila has two
  7SL RNA genes, modelled together as the RNA scaffold of SRP. Domain
  assignments follow the conserved mammalian SRP structure.
parts:
  - id: srp
    label: Signal recognition particle
    role: signal sequence recognition
    complex: true
    concepts:
      - {id: GO:0005786, label: "signal recognition particle, endoplasmic reticulum targeting"}
    parts:
      - id: srp_7sl_rna
        label: 7SL RNA
        role: SRP RNA scaffold
        genes: ["7SLRNA:CR32864", "7SLRNA:CR42652"]
        complex: false
      - id: srp_alu_domain
        label: SRP Alu domain proteins
        role: elongation arrest
        genes: [Srp9, Srp14]
      - id: srp_s_domain
        label: SRP S domain proteins
        role: signal sequence binding and receptor interaction
        genes: [Srp19, Srp54k, Srp68, Srp72]
        unit_functions:
          Srp54k: {id: GO:0003924, label: GTPase activity}
  - id: srp_receptor
    label: SRP receptor
    role: ER membrane docking of SRP
    group: SRPR
    complex: true
    complex_term: {id: GO:0005785, label: signal recognition particle receptor complex}
    unit_functions:
      SrpRalpha: {id: GO:0003924, label: GTPase activity}
      SrpRbeta: {id: GO:0003924, label: GTPase activity}
connections:
  - {source: srp, target: srp_receptor, connection_type: PRECEDES, description: SRP carrying a ribosome-nascent chain complex docks on the SRP receptor at the ER membrane.}