FIG 1.

Early stringent response to isoleucine starvation. (a) (p)ppGpp responses of the wild-type MG1655 strain (wt) and a strain with all 10 known toxin-antitoxin loci deleted (Δ10TA) to valine-induced isoleucine starvation at time zero. The levels of (p)ppGpp were normalized to the prestarved level for each strain. The triangles and squares represent average fold increases for three independent measurements, and the error bars represent standard errors. The simulated levels of (p)ppGpp from the model of the early stringent response were plotted as blue and red curves. (b) Schematic illustration of the regulatory network. (p)ppGpp synthesis is triggered by sudden aa starvation imposed on rapidly growing cells. The level of (p)ppGpp is self-amplified by RelA and SpoT, and (p)ppGpp induces transcriptional inhibition. (p)ppGpp also activates Lon protease to release toxins from the toxin-antitoxin complexes to deplete mRNA.