Letter to the editor: Characterization of mutations in the tryptophan operon of Escherichia coli by RNA nucleotide sequencing

The nucleotide sequences of operator-proximal tryptophan messenger RNA of Escherichia coli from strains with mutations very early in trpE have been determined. A frameshift mutant, trpE9777fs, has an additional A residue in the region coding for amino acids 4 and 5 of the trpE polypeptide. The other mutant, trpE9914am, exhibits an amber codon corresponding to the codon normally specifying amino acid residue 9 (glutamic acid) of the trpE polypeptide. These results demonstrate that the site of the trpE9777fs mutation precedes that of the trpE9914am mutation by 9 to 15 nucleotides.