Required for the lipid transport activity of the ALA/ALIS P4-ATPase complex. Interacts with ALA2 and ALA3 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. Belongs to the CDC50/LEM3 family.