Final answer:
The translocator in water-soluble ER proteins binds to signal recognition particles (SRPs) and the hydrophobic signal peptide. The SRP-ribosome complex attaches to an SRP receptor on the RER membrane for protein transfer.
Step-by-step explanation:
In the case of water-soluble ER proteins, the translocator binds to signal recognition particles (SRPs), which recognize the hydrophobic signal peptide on the protein.
The SRP-ribosome complex then binds to an SRP receptor on the rough endoplasmic reticulum (RER) membrane, allowing for the transfer of the protein into the lumen of the RER.