DNA methylation alters the pattern of spontaneous mutation in Escherichia coli cells (mutD) defective in DNA polymerase III proofreading
Department of Biochemistry and Molecular Pharmacology
Medical Subject Headings
Bacteriophages; Cloning, Molecular; DNA Polymerase III; DNA, Bacterial; Escherichia coli; Genes, Bacterial; Genes, Viral; Methylation; *Mutation; Phenotype; Plasmids; beta-Galactosidase
We have shown previously that dam mutants of Escherichia coli have a weak mutator phenotype which generates mostly transition mutations in the P22 mnt gene. In contrast, in mutD5 cells, which have a strong mutator phenotype, transversion mutations were the most prevalent. A dam-16 mutD5 strain, defective in both DNA polymerase III associated-proofreading and Dam-directed mismatch repair exhibits a strong mutator phenotype but, surprisingly, its mutation spectrum is similar to that of the dam rather than the mutD parent. The most likely explanation is that Dam-directed mismatch repair in the mutD5 strain corrects most of the potential transition mutations (therefore yielding transversions) in the newly synthesised strand. When the dam-16 allele is present together with mutD5 a reduced efficiency of repair as well as loss of strand discrimination and misdirected repair results in the appearance of transition mutations at high frequency.
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Citation: Mutat Res. 1991 Sep;264(1):15-23.
Palmer, Barry R. and Marinus, Martin G., "DNA methylation alters the pattern of spontaneous mutation in Escherichia coli cells (mutD) defective in DNA polymerase III proofreading" (1991). Biochemistry and Molecular Pharmacology Publications and Presentations. Paper 37.