CLONING, NUCLEOTIDE-SEQUENCE, AND CHARACTERIZATION OF MTR, THE STRUCTURAL GENE FOR A TRYPTOPHAN-SPECIFIC PERMEASE OF ESCHERICHIA-COLI K-12

The mtr gene of Escherichia coli K-12 encodes an L-tryptophan-specific permease. This gene was originally identified through the isolation of mutations in the 69-min region of the chromosome, closely linked to argG. Cells with lesions in mtr display a phenotype of 5-methyltryptophan resistance. The mtr gene was cloned by using the mini-Mu system. The amino acid sequence of Mtr (414 codons), deduced by DNA sequence analysis, was found to be 33% identical to that of another single-component transport protein, the tyrosine-specific permease, TyrP. The hydropathy plots of the two permeases were similar. Possible operator sites for the tyrosine and tryptophan repressors are situated within the region of DNA that is likely to be the mtr promoter.