All proteins destined for the ER have a unique hydrophobic signal sequence at their N-terminal. As soon as this signal sequence emerges from the ribosome, it is bound by the signal recognition particle or SRP — a ribonucleoprotein complex with a ladle-shaped structure. In addition to a signal sequence binding pocket, SRP also has a translation pause domain and a GTP -binding domain. The translation pause domain blocks the elongation factor binding site on the ribosome and arrests translation. After binding to the ribosome-nascent chain or RNC complex, the SRP changes conformation, exposing a receptor binding site. The SRP-RNC complex then uses a GTP-dependent interaction and docks at the SRP receptor present on the ER membrane. The SRP-SRP receptor complex then carries the ribosome and the target polypeptide chain to an adjacent translocon channel. The interaction of the SRP receptor with the translocon brings about a conformational change in the SRP,… unloading the RNC complex on the translocon. Following unloading, GTP hydrolysis dismantles the SRP-SRP receptor complex to recycle the components for the next ER protein targeting cycle.