title: Roles of RecA protein in spontaneous mutagenesis in Escherichia coli.
abstract: To verify the extent of contribution of spontaneous DNA lesions to spontaneous mutagenesis, we have developed a new genetic system to examine simultaneously both forward mutations and recombination events occurring within about 600 base pairs of a transgenic rpsL target sequence located on Escherichia coli chromosome. In a wild-type strain, the recombination events were occurring at a frequency comparable to that of point mutations within the rpsL sequence. When the cells were UV-irradiated, the recombination events were induced much more sharply than point mutations. In a recA null mutant, no recombination event was observed. These data suggest that the blockage of DNA replication, probably caused by spontaneous DNA lesions, occurs often in normally growing E. coli cells and is mainly processed by cellular functions requiring the RecA protein. However, the recA mutant strain showed elevated frequencies of single-base frameshifts and large deletions, implying a novel mutator action of this strain. A similar mutator action of the recA mutant was also observed with a plasmid-based rpsL mutation assay. Therefore, if the recombinogenic problems in DNA replication are not properly processed by the RecA function, these would be a potential source for mutagenesis leading to single-base frameshift and large deletion in E. coli. Furthermore, the single-base frameshifts induced in the recA-deficient cells appeared to be efficiently suppressed by the mutS-dependent mismatch repair system. Thus, it seems likely that the single-base frameshifts are derived from slippage errors that are not directly caused by DNA lesions but made indirectly during some kind of error-prone DNA synthesis in the recA mutant cells.
authors.affiliation: Department of Molecular Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kanie
authors.forename: Katsuyoshi
authors.initials: K
authors.lastname: Horibata
authors.forename: Mitsuoki
authors.initials: M
authors.lastname: Kawano
authors.forename: Asako
authors.initials: A
authors.lastname: Isogawa
authors.forename: Akiko
authors.initials: A
authors.lastname: Sakai
authors.forename: Nozomi
authors.initials: N
authors.lastname: Matsuo
authors.forename: Mari
authors.initials: M
authors.lastname: Nakanishi
authors.forename: Kimiko
authors.initials: K
authors.lastname: Hasegawa
authors.forename: Kaoru
authors.initials: K
authors.lastname: Yoshiyama
authors.forename: Hisaji
authors.initials: H
authors.lastname: Maki
mesh_terms: D001483:Base Sequence; D002876:Chromosomes, Bacterial; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D008954:Models, Biological; D008969:Molecular Sequence Data; D016296:Mutagenesis / Q000235:genetics / Q000502:physiology*; D020125:Mutation, Missense; D030781:Organisms, Genetically Modified; D010641:Phenotype; D011938:Rec A Recombinases / Q000235:genetics / Q000502:physiology*; D000091243:Ribosomal Protein S9; D012269:Ribosomal Proteins / Q000235:genetics
chemical_list: D029968:Escherichia coli Proteins; D000091243:Ribosomal Protein S9; D012269:Ribosomal Proteins; C000717190:RpsI protein, E coli; C506766:RpsL protein, E coli; D011938:Rec A Recombinases