Activation of the stringent response by loading of tRNA-RelA complexes at the ribosomal A-site

ABSTRACT: RelA/SpoT Homologs (RSHs) are ubiquitous bacterial enzymes that synthesize and hydrolyze (p)ppGpp in response to environmental challenges. Bacteria cannot survive in hosts and produce infection without activating the (p)ppGpp-mediated stringent response, but it is not yet understood how the enzymatic activities of RSHs are controlled. Using UV crosslinking and deep sequencing, we show that Escherichia coli RelA [(p)ppGpp synthetase I] interacts with uncharged tRNA during steady-state cell growth without being activated. Amino acid starvation leads to loading of cognate tRNA·RelA complexes at vacant ribosomal A-sites. In turn, RelA is activated and synthesizes (p)ppGpp. Mutation of a single, conserved residue in RelA simultaneously prevents tRNA binding, ribosome binding, and activation of RelA, showing that all three processes are interdependent. Our results support a model in which (p)ppGpp synthesis occurs by ribosome-bound RelA interacting with the Sarcin-Ricin Loop of 23S rRNA.

ORGANISM(S): Escherichia coli

PROVIDER: GSE108758 | GEO | 2018/04/05

REPOSITORIES: GEO