Stringent Response in E. coli

When nutrients are abundant, bacteria grow exponentially, rapidly synthesizing RNA and proteins for cell division.

During amino acid starvation, cells slow rRNA synthesis, inhibit cell division, and transition into the stationary phase.

In E. coli, when amino acid levels decrease, uncharged tRNAs accumulate and enter the ribosome, stalling translation.

Stalling activates RelA, which binds the ribosomes to synthesize a stringent response regulator called guanosine pentaphosphate from ATP and GTP.

Some bacteria utilize small alarmone synthetases to regulate guanosine pentaphosphate independently of ribosomal signaling.

Guanosine pentaphosphate shifts transcription toward amino acid biosynthesis and stress adaptation genes..

When nutrients become available again, SpoT, in E. coli, hydrolyzes guanosine pentaphosphate into GTP or GDP and inorganic phosphate, restoring normal cellular metabolism.

Elevated guanosine pentaphosphate levels are found in some bacteria that maintain dormancy under prolonged stress.