The Alarmones (P)Ppgpp Directly Regulate Translation Initiation During Entry Into Quiescence

Many bacteria exist in a state of metabolic quiescence where energy consumption must be minimized so as to maximize avail- able 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 down - regulation during the transition from growth to quiescence. We observe that when Bacillus subtilis exits rapid growth, a subpop- ulation of cells emerges with very low protein synthetic activity. This phenotypic heterogeneity requires the production of the nu- cleotides (p)ppGpp, which we show are sufficient to inhibit pro- tein synthesis in vivo. We then show that one of these molecules, ppGpp, inhibits protein synthesis by preventing the allosteric acti- vation of the essential GTPase Initiation Factor 2 (IF2) during trans- lation initiation. Finally, we demonstrate that the observed attenuation of protein synthesis during the entry into quiescence is a consequence of the direct interaction of (p)ppGpp and IF2.