AbstractThe plasmids harbouring therelA gene under an inducible promoter allowed us to increase the guanosine 5′‐diphosphate‐3′‐diphosphate (ppGpp) concentration inEscherichia colicells without any starvation and thus, to directly investigate the effect of ppGpp on DNA replication. We studied all types of replicons which were investigated previously in amino acid‐starved bacteria and found that ColE1,oriC, λ plasmid and pSC101 but not RK2 replicons are sensitive to high ppGpp level. To our knowledge, this paper presents the first direct evidence that replication of most, but not all, replicons is dependent on ppGpp concentration and thus, is under strin