A role for polyamines in the control of ppGpp levels in Escherichia coli

As an approach to understand the involvement of polyamines in the variation of intracellular guanosine 5'-diphosphate 3'-diphosphate (ppGpp) levels, kinetic studies with several polyamine-requiring relA and spoT Escherichia coli mutants have been carried out. The accumulation and turnover of the nucleotide have been followed under conditions of aminoacid depletion or energy source starvation. The results obtained strongly suggest an important role of the polycations mainly in the degradation of ppGpp, and also in its synthesis mediated by ppGpp synthetase I (PSI).