Nucleotide sequence and transcription of the phenylalanine and tyrosine operons of Escherichia coli K12

Abstract

A 4509 base-pair DNA fragment containing the phenylalanine and tyrosine operons of Escherichia coli K12 has been sequenced, and the pattern of transcription of these operons examined by S 1 mapping, primer extension and galK fusion analyses. The phe operon consists of promoter, operator, leader region containing the phe attenuator and the pheA gene encoding chorismate mutase/prephenate dehydratase. The tyr operon consists of promoter, operator, a short leader region without an attenuator, and two structural genes aroF and tyrA encoding the tyrosine-sensitive isoenzyme of 3-deoxy- d-arabinoheptulo-sonate-7-phosphate (DAHP) synthetase and chorismate mutase/prephenate dehydrogenase, respectively. A bidirectional transcription terminator occurs between the two operons. The predicted amino acid sequences of chorismate mutase/prephenate dehydrogenase and chorismate mutase/prephenate dehydratase are homologous at their N termini, while the tyrosine-sensitive isoenzyme of DAHP synthetase is closely homologous to the phenylalanine-sensitive isoenzyme encoded by aroG.