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Changes in DNA base sequence induced by targeted mutagenesis of lambda phage by ultraviolet light
Journal of Molecular Biology
|March 5, 1984
Summary
Ultraviolet light causes mutations in phage DNA primarily through pyrimidine (Pyr-Pyr) photoproducts. Pyr(6-4)Pyo photoproducts, not thymine dimers, are the main cause of these targeted mutations.
Area of Science:
- Molecular Biology
- Genetics
- Photochemistry
Background:
- Ultraviolet (UV) radiation induces DNA damage, leading to mutations.
- Understanding the specific DNA photoproducts responsible for mutagenesis is crucial.
Purpose of the Study:
- To identify the specific DNA photoproducts that cause targeted mutations in lambda phage DNA after UV irradiation.
- To differentiate the mutagenic potential of thymine-thymine cyclobutyl dimers versus Pyr(6-4)Pyo photoproducts.
Main Methods:
- Targeted mutagenesis of lambda phage using UV light.
- DNA sequencing of mutated cI gene to identify mutation types (transitions, transversions, frameshifts).
- Irradiation with specific wavelengths and photoreactive agents to isolate effects of different photoproducts.
Main Results:
- 63% of UV-induced mutations were base transitions, with others being transversions and frameshifts.
- Most mutations occurred at pyrimidine-pyrimidine (-Pyr-Pyr-) sequences.
- Irradiation conditions favoring thymine-thymine cyclobutyl dimers resulted mainly in transversions, not transitions.
Conclusions:
- Thymine-thymine cyclobutyl dimers are unlikely to be the primary cause of UV-induced base transitions.
- Pyrimidine (6-4) pyrimidone (Pyr(6-4)Pyo) photoproducts are strongly implicated as the mutagenic lesions responsible for UV-induced transitions in lambda phage DNA.