Operator mutations of the Escherichia coli aroF gene.

The Escherichia coli aroF and aroG genes encode the tyrosine-sensitive and the phenylalanine-sensitive 3-deoxy-D-arabino-heptulosonate 7-phosphate synthases, respectively, two of the three isoenzymes that control carbon flow through the shikimate pathway. Transcription of aroF and aroG is repressed by the tyrR gene product complexed to tyrosine or phenylalanine, respectively. Constitutive aroF mutants with lesions linked to aroF were isolated. The nucleotide sequences in the regulatory regions of aroF from six such mutants and from the parental wild type strain were determined. The mutations were found in two 18-base pair imperfect palindromes, called aroFo1 and aroFo2, which are located upstream of the aroF transcription start by 61 and 113 base pairs, respectively. Nuclease S1 mapping and analysis of in vitro run-off transcripts identified the 5'-end of the aroF transcript 51 base pairs upstream of the aroF translation start. The -35 region of the aroF promoter overlaps aroFo1. The aroFo1 and aroFo2 sequences are homologous to a single 18-base pair DNA segment preceding the coding sequence of aroG.