Signal recognition particle

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 core of the particle is universal, being conserved in all three kingdoms.

The SRP is found in the cytosol. In eukaryotes, it binds to the ER signal sequence found in an emerging secretory protein and subsequently delivers the protein along with the ribosomes creating it to the ER membrane.