Final answer:
A COPII-coated vesicle contains COPII complex components like Sar1 and Sec proteins, but not the clathrin adaptor protein AP-2, which is associated with clathrin-coated vesicles at the plasma membrane.
Step-by-step explanation:
The question is asking which of the specified proteins or protein complexes you would not find associated with a COPII-coated vesicle, which facilitates the transport of substances from the endoplasmic reticulum to the Golgi apparatus. A COPII-coated vesicle typically includes components like Sar1, Sec13/31, and Sec23/34, which are part of the COPII complex playing a crucial role in vesicle formation and cargo selection at the endoplasmic reticulum (ER). Conversely, AP-2 is part of the clathrin-associated adaptor protein complex involved in the formation of clathrin-coated vesicles at the plasma membrane, particularly in processes like receptor-mediated endocytosis. Thus, AP-2 is the element that you would not find associated with a COPII-coated vesicle. The vesicles coated by COPII are important for protein trafficking and ensuring that the protein cargo is correctly sorted for delivery to the Golgi apparatus. Additionally, COPII vesicles do not generally contain v-SNAREs; these are found in the membranes of vesicles already bound for fusion with a target membrane.