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Isolation of an Escherichia coli mutant which permits the high-level expression of a streptomycin-resistance gene derived from Pseudomonas aeruginosa.

Pretreatment with streptomycin at a low concentration influenced the susceptibility to streptomycin of a strain of Escherichia coli carrying a streptomycin-resistance plasmid, pSA1700, derived from Pseudomonas aeruginosa. This phenomenon was due to a mutation that occurred at about 10(-8)-10(-10) of frequency in a regulatory gene involved in gene expression on the chromosome of E. coli. A product encoded by the regulatory gene on the chromosome of E. coli might normally repress gene expression by binding to part of the promoter region of the streptomycin-resistance gene derived from P. aeruginosa.