Metabolism of Guanosine Tetraphosphate in Escherichia coli

In rel + strains of Escherichia coli guanosine 2′(3′)‐diphosphate‐5′‐diphosphate (ppGpp) was found to accumulate (a) during amino acid starvation of an auxotrophic strain, (b) during heating to the non‐permissive temperature of a val S ts strain, (c) during heating of a wild‐type strain to temperatures above 46°C and (d) during treatment with trimethoprim or hydroxylamine. A rapid decay of the accumulated ppGpp was observed after addition of chloramphenicol, tetracycline, fusidic acid, erythromycin, puromycin or colicin E3 to susceptible cultures. All of these antibiotics give a rapid and complete inhibition of protein synthesis. Streptomycin showed a delayed inhibitory action on protein synthesis and had little effect on the level of accumulated ppGpp. The addition of rifampicin also results in a delayed decay of ppGpp. These results indicate that the synthesis of ppGpp is independent of RNA synthesis, but suggest that a coupling exists between ppGpp formation and an idling reaction of one of the initiation steps of protein synthesis.