signal recognition particle

GO:0048500 · Ribonucleoprotein · Ribonucleoprotein complex · Proposed

A complex of protein and RNA which facilitates translocation of proteins across membranes. [GO:0048500]

Synonyms: SRP; bacterial signal recognition particle

Part of: GO:0005737 — cytoplasm (no local record)

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Components

Component	Type	Part of / acts on	Grounding	Genes	Stoichiometry	Essential	Role
SRP RNA	Rna	part of	`SO:0000590`			UNKNOWN	RNA scaffold that binds the SRP54/Ffh GTPase and promotes bacterial SRP-FtsY receptor handoff. `SO:0000590` SO:0000590 is the Sequence Ontology term for signal-recognition-particle RNA. `DOI:10.1016/j.bbamcr.2013.10.013` Saraogi and Shan 2014 reviewed the bacterial SRP as a minimal ribonucleoprotein containing 4.5S RNA and Ffh.
Ffh/SRP54 GTPase	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	ffh		UNKNOWN	Signal-sequence-binding SRP GTPase that recognizes ribosome-nascent-chain complexes and pairs with the FtsY receptor GTPase during delivery to the membrane translocon. `DOI:10.1016/j.bbamcr.2013.10.013` Saraogi and Shan 2014 reviewed Ffh as the conserved bacterial SRP protein subunit. `DOI:10.1093/emboj/16.16.4880` Powers and Walter 1997 reconstituted Escherichia coli SRP-dependent targeting from Ffh, 4.5S RNA, FtsY and a ribosome-nascent-chain substrate.

Taxonomic distribution

NCBITaxon:2 Bacteria — COMMON: This row captures the bacterial Ffh plus 4.5S RNA SRP particle; the archaeal and eukaryotic SRP expansions are left for follow-up curation. [DOI:10.1016/j.bbamcr.2013.10.013]

Canonical examples

NCBITaxon:562 Escherichia coli — Model bacterium in which purified Ffh, 4.5S RNA and FtsY were reconstituted as a cotranslational targeting system. [DOI:10.1093/emboj/16.16.4880]

Functions

protein targeting to membrane GO:0006612 — The bacterial SRP targets ribosome-nascent-chain complexes carrying inner-membrane protein substrates to the cytoplasmic-membrane translocon.
- GO:0006612 GO:0006612 is the Gene Ontology biological-process term for protein targeting to membrane.
- DOI:10.1093/emboj/16.16.4880 Powers and Walter 1997 showed that Escherichia coli Ffh, 4.5S RNA and FtsY catalyze cotranslational targeting of a ribosome-nascent-chain complex.

Mechanism graphs

Bacterial SRP delivers nascent membrane proteins to SecYEG (FUNCTION)

In bacteria, the Ffh/SRP RNA particle binds ribosome-nascent-chain complexes carrying hydrophobic signal sequences and hands them to the FtsY receptor for delivery to the SecYEG translocon.

Subject	Predicate	Object	Evidence
SRP RNA	assembles with	Ffh/SRP54 GTPase	`DOI:10.1016/j.bbamcr.2013.10.013` Saraogi and Shan 2014 reviewed the bacterial signal recognition particle as an Ffh and 4.5S RNA ribonucleoprotein.
Ffh/SRP54 GTPase	recognizes	ribosome-nascent-chain complex	`DOI:10.1016/j.bbamcr.2013.10.013` Saraogi and Shan 2014 reviewed Ffh/SRP54 recognition of signal sequences on ribosome-nascent-chain complexes.
signal recognition particle	docks with	FtsY SRP receptor	`DOI:10.1093/emboj/16.16.4880` Powers and Walter 1997 reconstituted targeting with Escherichia coli SRP and the FtsY receptor.
FtsY SRP receptor	delivers cargo to	SecYEG translocon complex	`DOI:10.1016/j.bbamcr.2013.10.013` Saraogi and Shan 2014 reviewed bacterial SRP delivery of membrane-protein substrates to the membrane translocation machinery through FtsY.
signal recognition particle	supports	protein targeting to membrane	`DOI:10.1093/emboj/16.16.4880` Powers and Walter 1997 reconstituted E. coli SRP-dependent cotranslational targeting.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral InterPro, Pfam or NCBIfam groundings for Ffh/SRP54 and decide how to represent archaeal and eukaryotic SRP proteins such as SRP19, SRP9 and SRP14. The first SRP record captures the conserved Ffh/SRP54 plus SRP RNA core and the bacterial Ffh-4.5S RNA system. Archaeal and eukaryotic SRPs have expanded protein compositions that should be curated as exact grounded components or child records only after their source-neutral family boundaries are verified.
INTERPRETATION (RESOLVED): Exclude the bacterial FtsY SRP receptor and SecYEG translocon from the signal recognition particle component list. FtsY and SecYEG are receptor or destination machinery for SRP-mediated targeting, not constituents of the SRP ribonucleoprotein.

Evidence

GO:0048500 Gene Ontology cellular-component term for the signal recognition particle.
GO:1990904 Gene Ontology cellular-component term for ribonucleoprotein complex.
GO:0005737 — cytoplasm Gene Ontology cellular-component term for cytoplasm, the direct part_of parent asserted on GO:0048500.
GO:0006612 Gene Ontology biological-process term for protein targeting to membrane.
SO:0000590 Sequence Ontology term for SRP RNA.
DOI:10.1016/j.bbamcr.2013.10.013 Saraogi and Shan 2014, Co-translational protein targeting to the bacterial membrane, Biochimica et Biophysica Acta.
DOI:10.1093/emboj/16.16.4880 Powers and Walter 1997, Co-translational protein targeting catalyzed by the Escherichia coli signal recognition particle and its receptor, EMBO Journal.
DOI:10.1146/annurev-biochem-072711-164732 Akopian, Shen, Zhang and Shan 2013, Signal Recognition Particle: An Essential Protein-Targeting Machine, Annual Review of Biochemistry.

Curation history

2026-09-23T04:11:05Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-23T04:13:05Z codex · EXPANDED_RECORD — Added SRP synonymy, GO ribonucleoprotein parentage, cytoplasm parthood, SRP RNA and Ffh/SRP54 core components, bacterial distribution, an Escherichia coli canonical example, protein-targeting function, GO/SO/DOI evidence, a bacterial SRP delivery graph and component-boundary discussions.
2026-09-23T04:15:06Z codex · FIX_ID_LABEL — Changed the GO:0048500 causal-graph node label from the narrowed bacterial signal recognition particle phrase to the exact signal recognition particle GO label.
2026-09-23T04:24:08Z codex · FIX_DISCUSSION_ANCHOR — Replaced the invalid bare components discussion anchor with the concrete bacterial SRP targeting graph anchor.
2026-09-23T04:32:49Z codex · RESOLVED_REVIEW — Resolved #1353 by narrowing the SRP RNA role to RNA scaffold and SRP-FtsY receptor handoff, and resolved #1354 by rewording the protein targeting function so ribosome-nascent-chain complexes carry rather than encode membrane-protein substrates.

Source: data/structures/ribonucleoprotein/signal_recognition_particle.yaml