Signal Recognition Particle 54kDa (SRP54)

The signal recognition particle (SRP) is a ribonucleoprotein complex that mediates the targeting of proteins to the endoplasmic reticulum (ER). The complex consists of a 7S (or 7SL) RNA and 6 different proteins, SRP9 , SRP14, SRP19, SRP54, SRP68, and SRP72. SRP54 is positioned at the exit site close to ribosomal proteins L23a and L35. When SRP54 contacts the signal recognition particle receptor, SRP54 is rearranged such that it is no longer close to L23a. This repositioning may allow the translocon to dock with the ribosome, leading to insertion of the signal peptide into the translocation channel.SRP54 binds to SRP RNA via the M-domain, but only in the presence of RNA-bound SRP19, and that it associates with the signal peptide of nascent polypeptide chains.