Site of Inhibition of Peptidoglycan Biosynthesis During the Stringent Response in Escherichia coli

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Abstract
The site of inhibition of peptidoglycan synthesis during the stringent response in E. coli was determined in strains which were auxotrophic for both lysine and diaminopimelic acid (DAP). Cells were labeled with [3H]DAP for 30-60 min in the presence and absence of required amino acids, and the cellular distribution of [3H]DAP was determined. In both stringent (rel+) and relaxed (relA) strains, amino acid deprivation did not inhibit the incorporation of [3H] DAP into the nucleotide precursor and lipid intermediate fractions. The amount of [3H]DAP incorporated into the peptidoglycan fraction by the amino acid-deprived relA strain was over 70% of the amount incorporated in the presence of required amino acids. The amounts of labeled peptidoglycan in amino acid-deprived rel+ strains were only 20-44% of the amounts synthesized in the presence of amino acids. A late step in peptidoglycan synthesis is apparently inhibited during the stringent response. The components of the lipid intermediate fraction synthesized by rel+ strains in the presence and absence of required amino acids were quantitated. Amino acid deprivation did not inhibit the synthesis of either the monosaccharide-pentapeptide or the disaccharide-pentapeptide derivatives of the lipid intermediate. Thus, the reaction which is most likely inhibited during the stringent response is the terminal one involving the incorporation of the disaccharide-pentapeptide into peptidoglycan.