What does the ribosome form with the translocator during protein synthesis?

The ribosome forms a tight seal with the translocator during protein synthesis to ensure that the newly synthesized polypeptide chain is properly directed into the endoplasmic reticulum (ER) without any leakage of the synthesized protein. This tight seal is crucial in maintaining the integrity of the environment within the ER and preventing the diffusion of ions and small molecules, which could disrupt the delicate process of protein folding and modification that occurs within this organelle.

By creating a barrier, the ribosome-translocator complex effectively allows only the nascent protein to pass through while keeping the internal environment of the ER distinct from the cytosol. This is essential for ensuring that proteins are correctly processed and folded as they are synthesized in the ribosome, thereby facilitating proper cellular function. The dynamic interaction between the ribosome and translocator is key to the process of co-translational translocation, where translation and translocation occur simultaneously.