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. Disruption of the gene leads to embryonic lethality during early gastrulation. Intestine-specific knockout mice display severe growth retardation due to reduced fat absorption and decrease in lipid release from the intestinal epithelium to the lymph and blood. Liver-specific knockout mice display impaired VLDL lipidation leading to reduced plasma triglyceride levels in the fasted state. Liver-specific knockout mice also display a disturbed glucose metabolism caused by a reduced plasma membrane localization of the glucose transporter GLUT2. Belongs to the small GTPase superfamily. Arf family.