Final answer:
Proteins destined for incorporation into membranes are initially trapped in the fatty acid interior of the membrane instead of being released into the lumen of the ER. This trapping occurs through the presence of a stop-transfer sequence, which is a hydrophobic domain within the polypeptide chain.
Step-by-step explanation:
Proteins destined for incorporation into membranes are initially trapped in the fatty acid interior of the membrane instead of being released into the lumen of the ER.
This trapping occurs through the presence of a stop-transfer sequence, which is a hydrophobic domain within the polypeptide chain. The stop-transfer sequence prevents the protein from passing completely through the membrane and allows it to be retained within the membrane.