Abstract:The coat protein complex II (COPII) transport proteins from endoplasmic reticulum (ER) to Golgi. COPII is an important component of the protein secretory pathway in eukaryotes and plays an essential role in maintaining the homeostasis of various intracellular organelles. COPII coat complex consists of five highly conserved cytosolic proteins: cytosolic GTPase Ras related protein 1 Sar 1, inner shell component Sec23-Sec24, and outer cage component Sec13-Sec31. Here, we discuss the processes of COPII formation, and review the research progress of each subunit of COPII, and the redundancy of COPII subunit in different species.