Signal recognition particle
When the SRP-ribosome complex binds to a cell membrane receptor, SRP releases the ribosome and drifts away. The ribosome resumes protein synthesis, but now the protein is moving through the SRP-receptor transmembrane pore. So, SRP directs the movement of proteins within the cell. It binds with a transmembrane pore. This allows the protein to cross the membrane to where it is needed. In eukaryotes, the target is the membrane of the endoplasmic reticulum (ER).