The role of energy-generating processes in the degradation of guanosine tetrophosphate, ppGpp, in Escherichia coli.

The effect of energy limitation on the intracellular level of guanosine 5'-diphosphate, 3'-diphosphate (ppGpp) was investigated. Glucose exhaustion, as well as uncoupling of oxidative phosphorylation, evokes an immediate increase in the ppGpp concentration. This increase is a consequence of a lowered degradation rate of the nucleotide. The level of ppGpp, which determines the rate of ribosomal RNA synthesis, is thus subject to a double control system: amino acyl-tRNA availability governs the rate of synthesis while energy metabolism governs the rate of degradation.