(p)ppGpp controls stringent factors by exploiting antagonistic allosteric coupling between catalytic domains

Escherichia coli RelA is a ribosomal factor with strong (p)ppGpp synthesis activity that is dramatically activated in the presence of deacylated tRNA in the ribosomal A-site. RelA is a unique enzyme in that it is directly positively regulated by its product, alarmone nucleotide (p)ppGpp. Using HDX-MS, mulecular docking, biochemsitry, and microbiology approaches, we localise the (p)ppGpp binding site of E. coli RelA and uncover the molecular mechanism of RelA regulation by the alarmone.