ADP-ribosylation factors (ARFs) are highly conserved guanine nucleotide-binding proteins that enhance the ADP-ribosyltransferase activity of cholera toxin. ARF抯 are important in eukaryotic vesicular trafficking pathways and activating phospholipase D. ARL4 (ADP-ribosylation factor-like protein 4A) is a member of the ARF-like protein (ARL) subfamily of small GTPases. It contains a C terminal nuclear localization signal (NLS) region that interacts with Importin-? ARL4 localizes to the nucleus and is found in a variety of tissues, but is predominantly expressed in spermatogonia and Sertoli cells. It is most closely related to ARL6 and ARL7. Unlike ARFs, ARL4 does not activate the cholera toxin ADP-ribosyltranferase. ARL4 may play a role in neurogenesis during embryonic development and somitogenesis in the early stages of adult spermatogenesis.