Final answer:
The retrieval signal is a sequence at the C-terminus of proteins meant to be retained in the endoplasmic reticulum that directs their localization and is usually removed once the proteins reach their intended destination.
Step-by-step explanation:
Proteins maintained in the membrane of the endoplasmic reticulum contain a short amino acid sequence at the C-terminus as a retrieval signal. This signal sequence is crucial for directing the protein to the correct cellular compartment. The specific sequence functions much like a 'train ticket', ensuring that the protein reaches its intended destination within the cell, such as the mitochondria, chloroplasts, or remains within the endoplasmic reticulum. After a protein reaches its destination, this signal sequence is typically removed.
The retrieval signal for proteins to be maintained in the membrane of the endoplasmic reticulum typically consists of KDEL or a related sequence at the C-terminus. The presence of this sequence facilitates recognition by cellular factors that ensure the protein's retention in the endoplasmic reticulum. The retrieval signal is a vital component of cellular organization and protein traffic within the endomembrane system.