The ADP-ribosylation factor (Arf) family are highly conserved members of the Ras superfamily of regulatory GTP-binding proteins. Arf proteins participate in routing of intracellular proteins to and within the Golgi complex. Cellular functions include maintenance of organelle integrity, coat protein assembly, as an activator of phospholipase D. The Arf family is divided functionally into the Arf and the Arf-like (Arl) proteins. The ARF proteins are categorized as class I (ARF1, ARF2,and ARF3), class II (ARF4 and ARF5) and class III (ARF6) and members of each class share a common gene organization.