Translocates 4-amino-4-deoxy-L-arabinose-phosphoundecaprenol (alpha-L-Ara4N-phosphoundecaprenol) from the cytoplasmic to the periplasmic side of the inner membrane. Bacterial outer membrane biogenesis; lipopolysaccharide biosynthesis. Heterodimer of ArnE and ArnF. Induced by BasR. Cells lacking this gene are polymyxin sensitive. Lipid A is no longer modified with L-Ara4N even though the level of the lipid-linked donor of the L-Ara4N moiety, alpha-L-Ara4N-phosphoundecaprenol, is not reduced. However, the alpha-L-Ara4N-phosphoundecaprenol is less concentrated on the periplasmic surface of the inner membrane when compared to wild-type. Belongs to the ArnF family.