Final answer:
Essential elements for protein import into the ER include the ER signal sequence, protein translocators, the SRP, and the SRP receptor; the nuclear import receptor is not required for this process.
Step-by-step explanation:
When considering the components necessary for the import of proteins into the Endoplasmic Reticulum (ER), all of the following are needed except for the nuclear import receptor. The essential elements for protein import into the ER include the ER signal sequence, which is a sequence at the beginning of the polypeptide that signals the ribosome to attach to the ER; protein translocators, which help in moving the protein across the ER membrane; the signal recognition particle (SRP), which binds to the signal sequence and pauses translation; and the SRP receptor, which is located on the RER membrane and binds the SRP-ribosome complex.
The nuclear import receptor, however, is involved in transporting proteins into the nucleus, not the ER, and therefore is the one not needed for ER protein import.