Correlation of Genes and Enzymes, and Studies on Regulation of the Aromatic Pathway in Salmonella

Polyauxotrophic aromatic mutants of Salmonella typhimurium , previously classified aro B, E, C, A , and D , were shown to be blocked in Reactions 2, 3, 4, 6, and 7, respectively. 3-Deoxy- d - arabino -heptulosonate 7-phosphate synthetase (Enzyme 1) was derepressed about 10-fold in wild type cells grown in the presence of all amino acids except phenylalanine, tyrosine, and tryptophan, and in leaky mutants grown with a limiting aromatic amino acid supplement. The first reaction was catalyzed by at least two separable isoenzymes which were under feedback control of phenylalanine or tyrosine. Enzymes 2, 3, 4, and 5 responded only slightly or not at all to end product starvation. Noncoordinate repression of the intermediate enzymes is in accord with the known observation that the genes specifying them are not linked.