Bacterial multi-drug resistance (mdr) is a very alarming and rapidly growing health problem that is a major obstacle in the treatment of most infectious diseases. This mufti-drug resistance is caused by the over-expression of mdr efflux pumps that are imbedded in the cell membranes of bacteria. An important class of mdr pumps belongs to the Major Facilitator Super-Family of transporters, which transport various substrates through the cell membrane using energy derived by coupling to H+ gradients. Our goal is to ascertain the structural components that are involved in the translocation of drug molecules through the lipid bilayer by mdr-MFS transporters, and to understand how these efflux pumps achieve their wide range of drug specificities. An important long-term objective is to provide a detailed structural framework for comprehending the general transport mechanisms that confer the multi-drug phenotype. A high-resolution atomic structure of a bacterial multi-drug resistance MFS transporter will also serve as an excellent model for other important MFS transporters that are involved in sugar, ion, amino acid, inorganic, and organic ion transport. An x-ray crystal structure of prokaryotic mdr-MFS transporter will provide a structural basis for the transport of substrate by homologous mammalian transporters, which are involved in diabetes, several intestinal diseases, heart failure, and renal disorders. Our specific aims are: 1. Over-expression and purification of several families of bacterial mdr-MFS transporters and their bacterial homologs using a "shot gun" approach. 2. Crystallization and x-ray data collection of mdr-MFS transporters. 3. x-ray structure determination and refinement of mdr-MFS transporters.