Even though we have these four different regions within that polypeptide chain, it's only a single subunit. But prokaryotic cells typically express ABC transporters that contain many subunits. So sometimes we have dimers, sometimes we have tetrimers and so forth. Now, the second major difference is, as the case is, with the MDR protein, again found in humans, this basically moves that particular substrate molecule from the inside to the outside of the cell. But usually typically in prokaryotic cells, this ABC transporter moves the substrate molecule from the outside to the inside of the cell in revert. So eukaryotic cells generally use ABC transporters to export the molecule out of the cell.