Trans-Golgi-associated GTPase that regulates protein sorting. Controls the targeting of ARL1 and its effector to the trans-Golgi. Required for the lipidation of chylomicrons in the intestine and required for VLDL lipidation in the liver. Interacts with SYS1. Located in the trans-Golgi in the GTP-bound active state. Belongs to the small GTPase superfamily. Arf family.