Functions as a (p)ppGpp synthase. 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. It is necessary for persistence in mice, essential for intracellular growth of Brucella and required for expression of the type IV secretion system VirB and therefore plays a role in adaptation of Brucella to its intracellular host environment. ATP + GTP = AMP + guanosine 3'-diphosphate 5'-triphosphate Cells show morphological abnormalities such as branching and swelling forms during vegetative growth. It is unable to persist during stationary phase, presumably because of nutrient limitation occurring during this growth phase. It shows an important growth defect in human HeLa cells and in ovine macrophages MOCL3. At four weeks post infection the number of viable bacteria (deletion mutant) in mouse spleen is markedly reduced compared to the wild-type. The deletion mutant shows very low levels or absence of VirB at all time points of growth. Belongs to the RelA/SpoT family.