摘要：To examine the role of the soxRS regulon in mutagenesis, we characterized the spontaneous mutations occurring in the endogenous tonB gene in the Δ soxR strain and the SoxS overproducing strain of Escherichia coli . Neither the Δ soxR strain nor the SoxS overproducing strain led to an enhancement or diminishment of the spontaneous mutation frequency. By DNA sequencing, we determined 50 spontaneous mutants from the Δ soxR strains, and found that 36% were both base substitutions and IS insertions, 14% frameshifts and 10% deletions. Among the base substitutions, G:C→T:A transversions and G:C→A:T transitions predominated, followed by A:T→T:A transversions. We determined 54 spontaneous mutants from the SoxS overproducing strains, and found that 37% were IS insertions, 31% base substitutions, 17% frameshifts, 9% deletions and 6% duplications. Among the base substitutions, G:C→T:A transversions dominated, followed by A:T →T:A transversions and G:C→A:T transitions. These results were similar to those from the soxRS strains. Thus, it is suggested that the soxRS -regulated genes do not play a significant role in the defense against spontaneous mutagenesis.
