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An Escherichia coli dnaE mutation with suppressor activity toward mutator mutD5
1Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709.
Journal of Bacteriology
|March 1, 1992
Summary
A mutation in the dnaE gene, termed dnaE910, was discovered to suppress the mutator phenotype of Escherichia coli mutD5. This antimutator DNA polymerase shows conditional effects depending on the growth medium.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- The Escherichia coli mutator mutD5 exhibits conditional mutator strength, being moderate in minimal media and strong in rich media.
- The mutD5 mutator phenotype is primarily due to a defect in the dnaQ gene, encoding the epsilon subunit of DNA polymerase III holoenzyme.
Purpose of the Study:
- To identify mutations that suppress the mutability of the Escherichia coli mutD5 strain.
- To characterize the mechanism by which suppression occurs and its effect on DNA polymerase III.
Main Methods:
- Genetic screening for suppressor mutations in a mutD5 background.
- Localization of the suppressor mutation to the dnaE gene.
- Characterization of the suppressor mutation's effect on growth, mutability, and temperature sensitivity.
Main Results:
- A mutation, dnaE910, in the dnaE gene (encoding the alpha subunit of DNA polymerase III) was identified as a suppressor of mutD5.
- dnaE910 conferred reduced mutability in mutD5 strains, with stronger suppression in minimal than rich media.
- The dnaE910 mutation also improved growth of the mutD5 strain and increased temperature sensitivity in various genetic backgrounds.
Conclusions:
- The dnaE910 allele encodes an antimutator DNA polymerase subunit.
- The antimutator effect of dnaE910 may involve enhanced nucleotide insertion fidelity or improved proofreading activity of DNA polymerase III.