Final answer:
Attaching an ER import signal to a cytosolic signal directs secretory polypeptides to the rough endoplasmic reticulum (RER). The signal peptide serves as a temporary 'traffic' signal and is removed by an RER-associated enzyme during the crossing of the RER membrane.
Step-by-step explanation:
Attaching an ER import signal to a cytosolic signal directs a growing secretory polypeptide to the rough endoplasmic reticulum (RER). The signal peptide is encoded by secretory protein genes and serves as a temporary 'traffic' signal.
It is removed by an RER-associated enzyme as the polypeptide crosses the RER membrane into the cisternal space. This process is part of the signal hypothesis proposed by Gunther Blobel and his colleagues.