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. guanosine 3',5'-bis(diphosphate) + H2O = diphosphate + GDP + H(+) Purine metabolism; ppGpp biosynthesis; ppGpp from GDP: step 1/1. Interacts with CgtA/Obg (AC Q9KUS8) in a yeast 2-hybrid assay. Essential for growth, it cannot be disrupted. It can be disrupted in a relA deletion strain (relA phosphorylates GTP to ppGpp). Belongs to the RelA/SpoT family.