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Specificity of spontaneous mutations induced in mutA mutator cells
Sergey Balashov1, M Zafri Humayun
1Department of Microbiology and Molecular Genetics, International Center for Public Health, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, 225 Warren Street, Newark, NJ 07101-1709, USA.
Mutation Research
|April 6, 2004
Summary
The mutA gene mutation in Escherichia coli causes a strong mutator phenotype by inducing mistranslation. This leads to a significant increase in specific DNA base substitutions, particularly transversions, similar to errors in DNA polymerase proofreading.
Area of Science:
- Molecular Biology
- Genetics
- Microbiology
Background:
- The mutator phenotype in Escherichia coli can arise from errors in DNA replication and repair.
- The glyV gene, specifically the mutA allele, is known to cause a mutator phenotype through tRNA misreading.
- Translational stress-induced mutagenesis (TSM) is a phenomenon where mistranslation leads to increased mutation rates.
Purpose of the Study:
- To determine the specificity of forward mutations in the lacI gene of mutA cells compared to wild-type cells.
- To investigate the types and frequencies of base substitutions, insertions, and deletions induced by the mutA allele.
- To compare the mutation spectrum of mutA cells with that of cells defective in DNA polymerase proofreading functions.
Main Methods:
- Analysis of forward mutations in the lacI gene of Escherichia coli.
- Quantification of base substitutions (transitions and transversions), insertions, and deletions in mutA and wild-type strains.
- Comparison of mutation spectra with strains carrying known defects in DNA polymerase III proofreading (dnaQ and dnaE alleles).
Main Results:
- mutA cells exhibited a 23-fold increase in base substitutions, with a 35-fold increase in transversions and a 13-fold increase in transitions.
- A significant 348-fold increase in A:T-->T:A transversions was observed, particularly at G:C-rich hotspot sequences (5'-CCGCGTGG).
- The mutation spectrum, especially the elevated transversions, closely resembled that seen in cells with defective DNA polymerase III proofreading (dnaQ and dnaE173).
Conclusions:
- The mutA allele induces a mutator phenotype characterized by a dramatic increase in specific types of DNA base substitutions, notably transversions.
- The observed mutation specificity suggests a link between tRNA-mediated mistranslation and errors in DNA replication fidelity.
- The findings highlight the similarity in mutation patterns between translational stress-induced mutagenesis and defects in DNA polymerase proofreading.