Involved in targeting and insertion of nascent membrane proteins into the cytoplasmic membrane. Acts as a receptor for the complex formed by the signal recognition particle (SRP) and the ribosome-nascent chain (RNC). Part of the signal recognition particle protein translocation system, which is composed of SRP and FtsY. Sensitive to endogenous proteolytic cleavage between residues 18 and 19 and between residues 86 and 87. Belongs to the GTP-binding SRP family. FtsY subfamily.