EVIDENCE FOR CHLORAMPHENICOL H+ ANTIPORT IN CMR (MDFA) SYSTEM OF ESCHERICHIA-COLI AND PROPERTIES OF THE ANTIPORTER/

We detected chloramphenicol/H+ antiport activity in membrane vesicles of Escherichia coli and cloned a gene for the antiporter from chromoso mal DNA of E. coli. introduction of the gene into E. coli cells confer red resistance to chloramphenicol and ethidium. A slight increase in r esistance to acridine orange was also observed. Elevated chloramphenic ol efflux and ethidium efflux were observed in cells harboring a plasm id carrying the gene. Addition of chloramphenicol to the assay mixture reduced the efflux of ethidium. Elevated chloramphenicol/H+ antiport activity was observed in membrane vesicles prepared from cells harbori ng the plasmid. The pH optimum for the activity was 6.5. We sequenced the gene and deduced the amino acid sequence of its product. A sequenc e homology search revealed that it was same as that of Cmr (or MdfA). Thus, it became clear that Cmr (MdfA) is the chloramphenicol(and ethid ium)/H+ antiporter.