p)ppGpp directly regulates translation initiation during entry into quiescence

Many bacteria exist in a state of metabolic quiescence where they must minimize energy consumption so as to maximize available resources over a potentially extended period of time. As protein synthesis is the most energy intensive metabolic process in a bacterial cell, it would be an appropriate target for downregulation during the transition from growth to quiescence. We find that when Bacillus subtilis exits growth, a subpopulation of cells emerges with very low levels of protein synthesis dependent on synthesis of the nucleotides (p)ppGpp. We show that (p)ppGpp inhibits protein synthesis in vivo and in vitro by preventing the allosteric activation of the essential GTPase Initiation Factor 2 (IF2) during translation initiation. Finally, we demonstrate that IF2 is an authentic in vivo target of (p)ppGpp during the entry into quiescence, thus providing a mechanistic basis for the observed attenuation of protein synthesis.