The effect of the stringent response on mutation rates in Escherichia coli K-12

The reversion rates of two isogenic Escherichia coli K-12 auxotrophs differing only in relA have been determined in the absence or presence of serine hydroxamate, which provokes the stringent response. Reversion rates of leuB- and argH- were significantly higher in the relA+ than in the relA- strain, and the reversion rates in both strains were enhanced by serine hydroxamate. A positive correlation was established between reversion rates and the synthesis of guanosine-5'-diphosphate-3'-diphosphate in the absence and presence of serine hydroxamate. It is proposed that mutation rates are dependent upon rates of transcription and upon the genes which regulate the level of the signal nucleotide, guanosine tetraphosphate.