ARL4D (ADP-ribosylation factor-like protein 4D) is a developmentally regulated member of the ADPribosylation factor/ARF-like protein (ARF/ARL) family of Ras-related GTPases. Small GTP-binding protein which cycles between an inactive GDP-bound and an active GTP-bound form, and the rate of cycling is regulated by guanine nucleotide exchange factors (GEF) and GTPase-activating proteins (GAP).