The tryptophan-specific permease gene, mtr, is differentially regulated by the tryptophan and tyrosine repressors in Escherichia coli K-12.

The regulation of transcription of the gene for the tryptophan-specific permease, mtr, was evaluated in several genetically marked Escherichia coli strains through the use of a single-copy lacZ reporter system. The expression of mtr was repressed 97-fold by tryptophan via the Trp repressor and induced 10-fold by phenylalanine or tyrosine via the Tyr repressor. By primer extension analysis two distinct mtr transcripts and their corresponding promoters were identified. One transcript was induced by the Tyr repressor. The tryptophan-dependent interaction of Trp repressor with an operator target within the mtr promoter was demonstrated by means of a restriction endonuclease protection assay.