Two types of small GTP-binding proteins, ADP-ribosylation factor (Arf) and secretion-associated and Ras-related (Sar) , are major regulators of vesicle biogenesis in intracellular traffic and are founding members of a growing family that also includes Arf-relatedproteins (Arp) and Arf-like (Arl) proteins. Sar1 functions as a molecular switch to control the assembly of protein coats (COPII) that direct vesicle budding from ER.
