ImrP and LmrA have been genetically and functionally characterised. The proteins have been solubilised from the membrane, purified and functionally reconstituted in liposomes. LmrP catalyses the excretion of lipophilic cationic in with protons and is compounds exchange responsible for L. lactis resistance to a variety of antibiotics, in particular belonging to the group of macrolides those and tetracyclins (M Putman, The other multidrug transporter of L. lactis, LmrA, is half the size of MDR1 P-glycoprotein. which is a the human heterologous dimer P-glycoprotein plays a crucial role in the resistance of cancer cells against chemotherapeutic agents. Surprisingly, LmrA has about 50% similarity with each half of P-glycoprotein and functions as an homologous dimer. These observations demonstrate that these types of MDRs have been extensively conserved all the way from bacteria to man. LmrA is not only a structural but also a functional homolog of P-glycoprotein LmrA extrudes the same substrates and is sensitive to the same modulators as P-glycoproteins