AROMATIC BIOSYNTHESIS V

Abstract
In double mutants of Escherichia coli, blocked both before and after 5-dehydroshikimic acid (DHS), DHS competitively interferes with the utilization of its own product, shikimic acid. Increasing ratios of DHS to shikimic acid prevent successively the conversion of the latter to tyrosine, phenylalanine, tryptophan, p-aminobenzoic acid, p-hydroxybenzoic acid, and an unknown 6th factor. There is a characteristic DHS/shikimic acid ratio for inhibiting each of these syntheses, ranging from 0.2 for tyrosine to 30 for p-hydroxybenzoic acid. Mutants blocked between DHS and shikimic acid accumulate DHS heavily; competitive interference of this compound with shikimic acid utilization explains why these strains cannot respond to shikimic acid as sole supplement. Double mutants obtained from these strains, with an additional block before DHS, differ from their parents in responding to shikimic acid alone; they can therefore be isolated simply by plating the parents on minimal medium supplemented with shikimic acid.

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