In eubacteria ppGpp (guanosine 3'-diphosphate 5'-diphosphate) is a mediator of the stringent response that coordinates a variety of cellular activities in response to changes in nutritional abundance. This enzyme catalyzes the formation of pppGpp which is then hydrolyzed to form ppGpp. Also plays a role in the reductive division that occurs during the initial phase of nutrient starvation. ATP + GTP = AMP + guanosine 3'-diphosphate 5'-triphosphate Purine metabolism; ppGpp biosynthesis; ppGpp from GTP: step 1/2. Mutants remain rod shaped, and do not acquire the typical coccoid morphology usually seen during starvation. Belongs to the RelA/SpoT family.