Functions as a (p)ppGpp synthase; GDP can be used instead of GTP, resulting in an increase of (p)ppGpp synthesis (PubMed:18067544). Overexpression in relA mutants (triple relA-yjbM-ywaC deletions and single relA deletions) leads to growth arrest; GTP levels fall drastically, various guanine-related nucleotides are synthesized (ppGp or pGpp), the cellular transcriptional profile changes dramatically and 70S ribosome dimerization occurs (PubMed:22950019). Overexpression in the presence of a wild-type relA gene does not have these effects (PubMed:22950019). 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. activities in response to changes in nutritional abundance. YwaC has probably a minor role in stringent response (PubMed:18067544). ATP + GTP = AMP + guanosine 3'-diphosphate 5'-triphosphate Purine metabolism; ppGpp biosynthesis; ppGpp from GTP: step 1/2. Homotetramer. Weakly expressed during exponential growth with a marked and transient increase at the onset of the stationary phase (PubMed:18067544). Protein expression is very low during the first 3.5 hours after inoculation (at protein level) (PubMed:22950019). Induced by alkaline shock (PubMed:18067544). No visible phenotype, double yjbM-ywaC and triple relA-yjbM-ywaC mutants are also viable (PubMed:18067544). The synthase activity of YwaC is weaker than that of YjbM (PubMed:18067544). Belongs to the RelA/SpoT family.