ADP-ribosylation factors (ARFs) are highly conserved guanine nucleotide binding proteins that enhance the ADP-ribosyltransferase activity of cholera toxin. ARFs are important in eukaryotic vesicular trafficking pathways and they play an essential role in the activation of phospholipase D (PC-PLD). ARL15 (ADP-ribosylation factor-like 15), is a member of the ARF family of the Ras superfamily of small GTPases that are known to be involved in multiple regulatory pathways altered in human carcinogenesis. Other members of this protein family include ARL11, thought to be a tumor suppressor and may play a role in the regulation of apoptosis, ARL2 which plays an important role in microtubule dynamics and cell cycle progression, and ARL4, which may play a role in neurogenesis during embryonic development. The gene encoding ARL15 maps to chromosome 5p15 in humans. At least three isoforms of ARL15 are known to exist.