A diagram cartoon showing SMR protein TM strand evolution to generate members of the BAT, and DMT protein families. SMR TM domains conversion is based on TM alignments to larger drug transporters shown in Figure 5. TM strands from a putative SMR protein are shown as filled rectangles and numbered according to their position within the protein. Unnumbered vertically lined rectangles indicate TM strands gained within BAT and DME proteins. N- and C-termini are no longer shown in the figure to account for topological orientations changes that may contribute to this process. An alternative SMR/PSMR protein fusion model is also shown based on SMR fusion alignments which may also contribute to a 10 TM stranded DMT protein. For this model, fusion of two PSMR sequences and the subsequent gain of TM domains show the formation of 10 TM domain DMT transporters.