title: Characterization of spontaneous mutation in the delta soxR and SoxS overproducing strains of Escherichia coli.
abstract: To examine the role of the soxRS regulon in mutagenesis, we characterized the spontaneous mutations occurring in the endogenous tonB gene in the delta soxR strain and the SoxS overproducing strain of Escherichia coli. Neither the delta 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 delta 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.
authors.affiliation: Department of Biomolecular Sciences, Graduate School of Life Sciences, Tohoku University, Miyagi 980-8577, Japan.
authors.forename: Eiji
authors.initials: E
authors.lastname: Yamamura
authors.forename: Eun Hye
authors.initials: EH
authors.lastname: Lee
authors.forename: Akihiro
authors.initials: A
authors.lastname: Kuzumaki
authors.forename: Norio
authors.initials: N
authors.lastname: Uematsu
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Nunoshiba
authors.forename: Masakado
authors.initials: M
authors.lastname: Kawata
authors.forename: Kazuo
authors.initials: K
authors.lastname: Yamamoto
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis*; D001483:Base Sequence / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000096:biosynthesis*; D009154:Mutation / Q000235:genetics*; D015534:Trans-Activators / Q000096:biosynthesis*; D014157:Transcription Factors / Q000096:biosynthesis*
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C070724:SoxR protein, Bacteria; C070725:SoxS protein, E coli