Required for the lipid transport activity of the ALA/ALIS P4-ATPase complex. Associates with ALA3 to form a stable complex. Interacts with ALA2 in a heterologous system. In a heterologous system, the final intracellular localization after exit from the endoplasmic reticulum is the prevacuolar compartment in the presence of ALA2 and the Golgi in the presence of ALA3. Expressed in roots, leaves, stems, flowers and siliques. Found in petals and sepals, but not in reproductive tissues. In siliques, detected in the upper part of the seed pod and in the area between the seed pod and the stem, but not in developing seeds. Strong expression in vascular shoot tissues and in stomatal guard cells of young rosettes leaves. In roots, expressed in cells surrounding the xylem and in central and peripheral columella cells. Belongs to the CDC50/LEM3 family.