Aromatic Biosynthesis

Abstract
Mutants of Escherichia coli, which cannot utilize shikimic acid because of an inhibitory effect of 5-dehydroshikimic acid (DHS), give rise to secondary mutants which grow on min. medium supplemented with shikimic acid. Quantitative assays for DHS were made with strain 156-53 which accumulates DHS and cannot grow on shikimic acid, and with 2 of its secondary mutants which grow on shikimic acid. On secondary mutant (156-53 D2), which was doubly blocked, did not accumulate DHS, whereas the other (156-53 R11) accumulated as much as the parent strain. Strains 156-53 and 156-53 Rll have quantitatively identical requirements for 5 aromatic metabolites. When grown in a liquid medium supplemented only by shikimic acid, strain 156-53 does not show any perceptible growth, whereas strain 156-53 Rll grows more rapidly than the doubly blocked mutant 156-53 D2, indicating that 156-53 Rll is resistant to inhibition by DHS. The possible mechanisms of resistance in the DHS-resistant strain are discussed and applied to the general phenomenon of drug resistance.

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