Regulation of the Salmonella typhimurium aroF gene in Escherichia coli.

The Salmonella typhimurium aroF gene, encoding the tyrosine-sensitive 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP) synthase, was localized to a chromosomal PstI fragment by Southern blotting with an Escherichia coli aroF probe. This fragment was cloned by screening a plasmid library for complementation of an E. coli aroF mutant. The nucleotide sequence of S. typhimurium aroF was determined and compared with its E. coli homolog. The nucleotide sequences are 85.1% identical, and the corresponding amino acid sequences are 96.1% identical. The E. coli genes encoding the three DAHP synthase isoenzymes are evolutionarily more distant from one another than are the homologous aroF genes of E. coli and S. typhimurium. The S. typhimurium aroF regulatory region contains three imperfect palindromes, two upstream of the promoter and one overlapping the promoter, that are nearly identical to operators aroFo1, aroFo2, and TyrR box 1 of E. coli. The aroFo1 and aroFo2 sequences of the two organisms are each separated by three turns of the DNA helix with no sequence similarity. The 5' ends of the aroF transcripts for both organisms contain untranslated regions with potential stem-loop structures. Translational fusions of the aroF regulatory regions to lacZ were constructed and then introduced in single copy into the E. coli chromosome. beta-Galactosidase assays for tyrR-mediated regulation of aroF-lacZ expression revealed that the E. coli TyrR repressor apparently recognizes the operators of both organisms with about equal efficiency.