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Mutagenic spectrum resulting from DNA damage by oxygen radicals
T J McBride1, B D Preston, L A Loeb
1Joseph Gottstein Memorial Cancer Research Laboratory, Department of Pathology, University of Washington, Seattle 98195.
Biochemistry
|January 8, 1991
Summary
Oxygen free radicals cause DNA damage and mutations. This study reveals that iron (Fe2+) and oxygen generate these radicals, leading to specific DNA changes like G-C transversions, potentially causing spontaneous mutations.
Area of Science:
- Biochemistry
- Molecular Biology
- Genetics
Background:
- Oxygen free radicals are highly reactive and can damage DNA, leading to mutations.
- Understanding the specific types of DNA damage caused by these radicals is crucial for comprehending mutagenesis.
Purpose of the Study:
- To determine the mutagenic spectrum of oxygen free radicals generated by Fe2+ and oxygen.
- To investigate the types of DNA mutations induced by these radicals in M13mp2 DNA.
Main Methods:
- Incubation of single-stranded M13mp2 DNA with Fe2+ under aerobic conditions to produce oxygen free radicals.
- Transfection of Fe2+-treated DNA into Escherichia coli and identification of mutants in the lac Z alpha gene.
- Analysis of nucleotide sequences of mutants to characterize the types of DNA alterations.
Main Results:
- Fe2+/oxygen treatment significantly increased mutant frequency (20- to 80-fold) compared to untreated DNA.
- Mutagenesis was enhanced by UV irradiation, inducing the SOS response.
- The majority (94%) of mutations were single-base substitutions, predominantly G----C transversions, followed by C----T and G----T transversions.
- Mutations clustered at specific gene positions, indicating nonrandom DNA damage.
Conclusions:
- Oxygen free radicals generated by Fe2+ are potent mutagens, primarily causing single-base substitutions.
- The identified mutational spectrum suggests that Fe2+/oxygen-induced DNA lesions are promutagenic and may contribute to spontaneous mutations.
- Antioxidant enzymes like catalase and superoxide dismutase can mitigate this type of mutagenesis.