Final answer:
Sec13 and Sec31 coat proteins are involved in initiating vesicle budding, specifically as components of the COPII complex, which is essential for intracellular protein transport from the RER to the Golgi apparatus.
Step-by-step explanation:
Coat proteins such as Sec13 and Sec31 are involved in initiating vesicle budding from the endoplasmic reticulum or the Golgi apparatus. They are part of the COPII complex, which is essential in the formation of transport vesicles that deliver proteins from the rough endoplasmic reticulum (RER) to the Golgi apparatus. The process that these proteins assist with is critical for maintaining the intracellular transport and proper sorting of proteins within the cell.