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. Belongs to the ArnF family. Compared to other bacterial ArnF, it has a divergent C-terminal domain. The upstream arnE gene has a premature stop codon and an internal deletion; as the 2 proteins form a heterodimer, ArnF probably does not accumulate to high levels.