Regulation of ornithine decarboxylase activity by guanine nucleotides: in vivo test in potassium-depleted Escherichia coli.

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Abstract
The observation that GTP is an activator and guanosine 5''-diphosphate-3''-diphosphate (ppGpp) is an inhibitor of ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) of E. coli was confirmed. The hypothesis that synthesis of polyamine and RNA in E. coli is regulated in vivo by these nucleotides was tested in E. coli B-207. On transfer of this K+-requiring, amino-acid-deficient stringent strain from K+-medium to Na+-medium, the organism stops protein synthesis, maintains a high rate of RNA synthesis, and increases putrescine synthesis from ornithine manyfold. Under these conditions, the cells do not markedly change their contents of GTP and ppGpp. The proposed mechanism of regulation of RNA and putrescine synthesis by guanine nucleotides may not explain the metabolic phenomena observed in this organism during K+ deficiency. Amino acid depletion in K+-medium results in a marked increase in ppGpp.