title: Roles of two types of O6-methylguanine-DNA methyltransferases in DNA repair.
abstract: Escherichia coli possesses 2 types of O6-methylguanine-DNA methyltransferases, one inducible and the other constitutive. These enzymes are coded by the ada and the ogt genes, respectively. Using a synthetic ogt-specific probe, we mapped ogt at 29.4 min, near the 5'-flanking region of the nirR gene, on the E. coli chromosome. To elucidate the roles of the 2 types of methyltransferases in DNA repair, we constructed mutant strains which lack either one or both of the genes. In either the ada+ or the ada- background, the ogt mutation had no effect on cell survival after N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) treatment. On the other hand, ada- ogt- cells were more prone to mutation as compared to the ada- ogt+ cells exposed to MNNG. The frequency of spontaneous mutation of cells defective in either one or both of the genes was the same, however, the introduction of the ogt+ plasmid into the cells produced a 2-3-fold decrease in the frequency of spontaneous mutation. O6-Methylguanine-DNA methyltransferases appear to eliminate premutagenic DNA lesions not only from cells exposed to alkylating agents but also from those grown in the absence of the agents.
authors.affiliation: Department of Biochemistry, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Takano
authors.forename: T
authors.initials: T
authors.lastname: Nakamura
authors.forename: M
authors.initials: M
authors.lastname: Sekiguchi
mesh_terms: D001483:Base Sequence; D015139:Blotting, Southern; D002874:Chromosome Mapping; D002876:Chromosomes, Bacterial; D003001:Cloning, Molecular; D004260:DNA Repair; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D005798:Genes, Bacterial; D008769:Methylnitronitrosoguanidine / Q000494:pharmacology; D008780:Methyltransferases / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D019853:O(6)-Methylguanine-DNA Methyltransferase; D015345:Oligonucleotide Probes; D010957:Plasmids; D015183:Restriction Mapping
chemical_list: D015345:Oligonucleotide Probes; D008769:Methylnitronitrosoguanidine; D008780:Methyltransferases; D019853:O(6)-Methylguanine-DNA Methyltransferase