The ADP-ribosylation factor (ARF) protein family are structurally and functionally conserved members of the Ras superfamily of regulatory GTP-binding proteins. ARFs influence vesicle trafficking and signal transduction in eukaryotic cells and they play a central role in the maintenance of organelle integrity, assembly of coat proteins and activation of phospholipase D (PC-PLD). ARFRP1 (ADP-ribosylation factor related protein 1), also known as ARP or ARL18, is a 201 amino acid membrane-associated GTPase that localizes to the plasma membrane and the Golgi apparatus and is related to the ARF family of regulatory proteins. Expressed in a variety of tissues, ARFRP1 interacts with SYS1 and is thought to be involved in plasma membrane-related signaling events. ARFRP1 exists as multiple alternatively spliced isoforms and is encoded by a gene which maps to a gene cluster on chromosome 20 that is commonly overexpressed in tumors, suggesting a role for ARFRP1 in carcinogenesis.