Constitutive and repressivle enzymes of the common pathway of aromatic biosynthesis in Escherichia coli K-12: regulation of enzyme synthesis at different growth rates.

Synthesis of five of the enzymes of the common pathway of aromatic biosynthesis has been shown to be unaffected by either the aromatic amino acids--the product of the first reaction (3-deoxy-D-arabinoheptulosonic acid-7-phosphate) or the product of the last reaction (chorismate)--or by the state of regulator gene loci tyrR. On the other hand, the rate of synthesis of these enzymes, and of several other enzymes for which repression control was inactive because of mutations in relevant regulator genes, was found to change with growth rate. These changes were found to correlate at faster growth rates than those observed in glucose minimal medium with the alterations in the relative frequencies of the corresponding structural genes which occur at these growth rates. It was found that when wild-type cells were grown at these faster growth rates in medium lacking the aromatic amino acids, complete derepression of the tyrosine-inhibitable 3-deoxy-D-arabinoheptulosonic acid-7-phosphate synthetase occurred, in strong contrast to the situation when wild-type cells are grown in glucose minimal medium.