Signal recognition particle

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signal recognition particle 9kDa
Identifiers
Symbol(s)	SRP9
Entrez	6726
OMIM	600707
RefSeq	NM_003133
UniProt	P49458
Other data
Locus	Chr. 1 q42.12

signal recognition particle 14kDa
Identifiers
Symbol(s)	SRP14
Entrez	6727
OMIM	600708
RefSeq	NM_003134
UniProt	P37108
Other data
Locus	Chr. 15 q22

signal recognition particle 19kDa
Identifiers
Symbol(s)	SRP19
Entrez	6728
OMIM	182175
RefSeq	NM_003135
UniProt	P09132
Other data
Locus	Chr. 5 q21-q22

signal recognition particle 54kDa
Identifiers
Symbol(s)	SRP54
Entrez	6729
OMIM	604857
RefSeq	NM_003136
UniProt	P61011
Other data
Locus	Chr. 14 q13.2

signal recognition particle 68kDa
Identifiers
Symbol(s)	SRP68
Entrez	6730
OMIM	604858
RefSeq	NM_014230
UniProt	Q9UHB9
Other data
Locus	Chr. 17 q25.1

signal recognition particle 72kDa
Identifiers
Symbol(s)	SRP72
Entrez	6731
OMIM	602122
RefSeq	NM_006947
UniProt	O76094
Other data
Locus	Chr. 4 q11

The signal recognition particle (SRP) is a protein-RNA complex that recognizes and transports specific proteins to the endoplasmic reticulum in eukaryotes and the plasma membrane in prokaryotes. The eukaryotic SRP is composed of six distinct polypeptides bound to an RNA molecule, with GTPase activity. In the GTP-bound state, it recognizes an endoplasmic reticulum signal sequence of eight or more nonpolar amino acid residues at its center.[1] It transiently binds to the endoplasmic reticulum signal sequence in a nascent protein, to the large ribosomal unit, and to the SRP receptor. The core of the SRP is universal, being conserved in all three kingdoms.

The SRP is found in the cytosol. In eukaryotes, it binds to the endoplasmic reticulum signal sequence found in an emerging secretory protein and subsequently delivers the protein along with the ribosome creating it to the endoplasmic reticulum membrane. When SRP binds the endoplasmic reticulum signal sequence, it also binds the ribosome and thereby pauses translation until the entire SRP-bound translation complex is transported to the endoplasmic reticulum, where translation resumes.[2]

SRP and its receptor initiate the transfer of the nascent chain across the endoplasmic reticulum membrane. Once the chain reaches the translocon, SRP and its receptor both hydrolyze their bound GTP to GDP, then dislocate allowing translation to restart.