Nucleotide sequence of region preceding trp mRNA initiation site and its role in promoter and operator function

The nucleotide sequence of the region preceding the transcription initiation site of the tryptophan operon of Escherichia coli was determined. Essentially all of the trp operator precedes the transcribed portion of the operon. The deduced sequence contains the recognition site of endonuclease Hpa I. This site is protected from Hpa I cleavage by RNA polymerase and by trp repressor. Regions of 2-fold symmetry are present in the DNA sequence.