The signal recognition particle (SRP) is an abundant, cytosolic, universally conserved ribonucleoprotein (protein-RNA complex) that recognizes and targets specific proteins to the endoplasmic reticulum in eukaryotes and the plasma membrane in prokaryotes.
[1] The function of SRP was discovered by the study of processed and unprocessed secretory proteins, particularly immunoglobulin light chains;[2] and bovine preprolactin.
Newly synthesized proteins in eukaryotes carry N-terminal hydrophobic signal sequences, which are bound by SRP when they emerge from the ribosome.
[11][12] The SRP-SRP receptor complex dissociates via GTP hydrolysis and the cycle of SRP-mediated protein translocation continues.
The SRP54-SRP RNA core with GTPase activity is shared in all cellular life, but some subunit polypeptides are specific to eukaryotes.