The stringent response is a key regulatory reaction exhibited by bacteria in response to amino acid deprivation or carbon, nitrogen and phosphate limitation. In E. coli, the products of the relA and spoT genes regulate accumulation of the effector molecules of the stringent response--guanosine tetra- and pentaphosphates (ppGpp and pppGpp respectively). These unusual hyperphosphorylated nucleotides bind directly to the bacterial RNA polymerase and change transcriptional activity of some genes--transcription repression of genes associated with the translational apparatus and the simultaneous upregulation of genes encoding metabolic enzymes, especially those involved in amino acid biosynthesis, protein hydrolysis and coding for the sigma S factor. Sigma S factor binds to the core of the bacterial RNA polymerase and induce stationary-phase-specific and stress-response-specific genes expression.