Coat Protein II (COPII) is a protein complex that plays a crucial role in the transport of proteins from the endoplasmic reticulum (ER) to the Golgi apparatus in eukaryotic cells. It is essential for the formation of transport vesicles that carry newly synthesized proteins, ensuring they reach their correct destinations within the cell. The COPII complex is composed of several proteins, including Sar1, Sec23, Sec24, Sec13, and Sec31. These proteins work together to coat the vesicles, facilitating their budding from the ER membrane. This process is vital for maintaining cellular function and communication.