The Escherichia coli cmlA Gene Encodes the Multidrug Efflux Pump Cmr/MdfA and Is Responsible for Isopropyl-β-d-Thiogalactopyranoside Exclusion and Spectinomycin Sensitivity

Expression of cloned genes from isopropyl-β-d-thiogalactopyranoside (IPTG)-regulated promoters is lowered when the Escherichia coli CmlA/Cmr/MdfA efflux pump is overexpressed, probably due to IPTG exclusion from the cytoplasm. The previously reported cmlA1 mutation confers a similar phenotype. cmlA1 contains an IS30 insertion upstream of cmr/mdfA, which creates a putative promoter. CmlA overproduction also causes spectinomycin hypersensitivity.