Mitomycin resistance in Streptomyces lavendulae includes a novel drug-binding-protein-dependent export system

Sequence analysis of Streptomyces lavendulae NRRL 2564 chromosomal DNA adja cent to the mitomycin resistance locus rnrd (encoding a previously describe d mitomycin-binding protein [P. Sheldon, D. A. Johnson, P. R. August, H.-W. Liu, and D. H. Sherman, J. Bacteriol. 179:1796-1804, 1997]) revealed a put ative mitomycin C (MC) transport gene (I,lct) encoding a hydrophobic polype ptide that has significant amino acid sequence similarity with several acti nomycete antibiotic export proteins. Disruption of met by insertional inact ivation resulted in an S. lavendulae mutant strain that was considerably mo re sensitive to MC. Expression of mct in Escherichia coli conferred a fivef old increase in cellular resistance to MC, led to the synthesis of a membra ne-associated protein, and correlated with reduced intracellular accumulati on of the drug. Coexpression of met and mrd in E. coli resulted in a 150-fo ld increase in resistance, as well as reduced intracellular accumulation of MC. Taken together, these data provide evidence that MRD and Met function as components of a novel drug export system specific to the mitomycins.