The influence of the reLA gene on lipopolysaccharide (LPS) biosynthesis and release by Escherichia coli and Salmonella typhimurium was investigated. Similar results were obtained with both species. The incorporation of [3H]galactose into LPS by galE mutants was inhibited by at least 50% (as compared with normal growing controls) during amino acid deprivation of relA+ strains. This inhibition could be prevented by the treatment of the amino acid-deprived reLA+ bacteria with chloramphenicol, a known antagonist of the stringent control mechanism. Furthermore, LPS biosynthesis was not inhibited during amino acid deprivation of isogenic reLA mutant strains. These results indicate that LPS synthesis is regulated by the stringent control mechanism.Normal growing cells of both relA + and relA strains released LPS into the culture fluid at low rates. Amino acid deprivation stimulated the rate of LPS release by reLA mutants but not by relA+ bacteria. Chloramphenicol treatment markedly stimulated the release of cell-bound LPS by amino acid-deprived relA+ cells. Thus, a low rate of LPS release was characteristic of normal growth and could be increased in nongrowing cells by relaxing the control of LPS synthesis.During amino acid deprivation, the syntheses of several classes of macromolecules (e.g., stable RNA species, phospholipids, and peptidoglycan) are inhibited by a mechanism known as stringent control in relA+ strains of Escherichia coli (1,5). In contrast, the syntheses of these macromolecules continue in amino acid-deprived relA mutants, and this phenomenon is referred to as relaxed control. Two novel nucleotides, GTP 3'-diphosphate (pppGpp) and GDP 3'-diphosphate (ppGpp), accumulate during amino acid deprivation in relA+ bacteria but not in relA mutants, and at least one of these nucleotides may be the mediator of stringent control. Chloramphenicol is an antagonist of stringent control; i.e., treatment of amino acid-deprived relA+ bacteria with chloramphenicol prevents the accumulation of pppGpp and ppGpp and results in relaxed control.The possibility that lipopolysaccharide (LPS) synthesis in E. coli is regulated by the stringent control mechanism has been previously investigated in several laboratories (3, Bacterial strains. Strains IT5 (hisT1504 hisC508 galE) and IT18 (hisT1504 hisC508 galE relA2J::TnlO) were derivatives of S. typhimurium LT2. Strain IT18 was constructed by transducing the relA2J::TnlO marker from strain TT7428 (obtained from J. R. Roth, University of Utah, Salt Lake City) into strain IT5 with phage P22. The experiments described in this paper were originally performed with E. coli K-12 strains VC3 (thi-l lysA23 galE15) and VC50 (thi-1 lysA23 galE15 galK relA2). We noted that the rate of [3HJgalactose incorporation into LPS by strain VC50 was only about 20% of the rate in strain VC3. We now attribute the inefficient incorporation of galactose by strain VC50 to a spontaneous mutation in galK which apparently arose during laboratory subculture and which we were originally unaware of (we are indeb...
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