COPII is a protein complex that plays a crucial role in the transport of proteins from the endoplasmic reticulum (ER) to the Golgi apparatus. It is essential for the secretion of proteins and the proper functioning of cells. The COPII complex assembles on the ER membrane, forming vesicles that encapsulate the proteins destined for transport. Once the vesicles are formed, they bud off from the ER and travel to the Golgi apparatus, where the proteins are further processed and sorted for their final destinations. This transport mechanism is vital for maintaining cellular functions and ensuring that proteins reach their appropriate locations within the cell or outside of it.