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

Abstract

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.

Increased transcription rates correlate with increased reversion rates in leuB and argH Escherichia coli auxotrophs

“…Only those cells that revert to prototrophy survive. When cells were starved for leucine, the reversion rate of leuB6 in CP78 was sevenfold higher than that in CP79 (Table 2; Wright, 1996). By comparing strains isogenic except for relA, we have shown that the strain able to activate leuB transcription with ppGpp had a higher mutation rate.…”

“…Conditions for growth and determination of mutation rates have been previously described (Wright, 1996;Wright & Minnick, 1997;Wright et al, 1999). A large culture was inoculated with cells from a 7 h old nutrient agar plate and 1?5 ml aliquots were distributed into 40 2 cm diameter test tubes, which were shaken at a 45u angle at 37 uC until the supply of the limiting amino acid was exhausted and growth ceased.…”

“…Cells were grown in minimal medium as previously described (Wright, 1996) with 0?05 M MES (pH 6?5) and 0?05 M KH 2 PO 4 substituted for 0?04 M sodium phosphate buffer (pH 6?5). When cells were to be starved for an amino acid, it was present at 0?2 mM in the growth medium.…”

“…Reversion rates for amino acid auxotrophs were determined previously (Wright, 1996) by growing the cells to stationary phase in a limiting amount of the required amino acid and then plating to minimal medium lacking that amino acid. Only those cells that revert to prototrophy survive.…”

“…1(a) and mutation rates from Wright (1996). The increase in argH mRNA at 12 min of arginine starvation (Fig.…”