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Mutations induced by gamma-irradiation of M13 bacteriophages containing single-stranded DNA
J E Braun1, E J Westmijze, M V Lafleur
1Department of Medical Oncology, Vrije Universiteit, Amsterdam, The Netherlands.
Abstract:
Oxygenated suspensions of M13 bacteriophages, containing single-stranded M13mp10 DNA, were gamma-irradiated followed by infection of E. coli cells. Mutants in the mutational target sequence, which consists of the lac promoter /operator region, the lacZ alpha gene, and a 144 bp inframe insert in the lacZ alpha gene, were selected and characterized. Except for three one-base deletions, all of the 51 mutations characterized were base substitutions. All base substitutions appeared to involve guanines and cytosines and none affect adenines and thymines. Since most of the known repair systems do not act on single-stranded DNA, the conclusion can be drawn that radiation induces under these conditions only mutagenic damages on guanine and cytosine. Although all possible G- and C-transversions and transitions were found, there is a strong preference for G-->C and G-->T transversions (21 and 25% of all base substitutions, respectively) and C-->T transitions (48% of all base substitutions). These results indicate, that the G/C-->C/G and G/C-->T/A transversions, found after irradiation of double-stranded M13 DNA, are mainly due to radiation guanine products, whereas cytosine damage is mainly responsible for G/C-->A/T transitions.
Insights
Gamma irradiation of M13 bacteriophage DNA primarily causes mutagenic damage to guanine and cytosine bases. This study reveals specific base substitution patterns, highlighting radiation-induced DNA mutations in single-stranded DNA.
Area of Science:
- Molecular Biology
- Radiation Biology
- Genetics
Background:
- M13 bacteriophages contain single-stranded DNA, making them a useful model for studying DNA damage and mutation.
- Gamma irradiation is a known mutagenic agent, but its specific effects on single-stranded DNA are less understood.
- Understanding radiation-induced mutations is crucial for fields ranging from radiation protection to cancer research.
Purpose of the Study:
- To investigate the types and patterns of mutations induced by gamma irradiation in single-stranded M13mp10 DNA.
- To determine which DNA bases (adenine, thymine, guanine, cytosine) are most affected by gamma irradiation in this system.
- To elucidate the role of specific base damages (e.g., guanine vs. cytosine) in observed mutation spectra.
Main Methods:
- Gamma irradiation of M13 bacteriophage suspensions containing single-stranded M13mp10 DNA.
- Infection of E. coli cells with irradiated phages to allow for mutant selection.
- Characterization of mutations within a specific target sequence (lac promoter/operator, lacZ alpha gene, and insert).
- Analysis of mutation types, focusing on base substitutions and their specific base pair changes.
Main Results:
- The vast majority of mutations were base substitutions (51 out of 51 characterized).
- All observed base substitutions involved guanine (G) and cytosine (C) bases; adenine (A) and thymine (T) were unaffected.
- A strong preference for G-->C and G-->T transversions (21% and 25%) and C-->T transitions (48%) was observed.
- Specific transversions (G/C-->C/G, G/C-->T/A) were mainly attributed to guanine damage, while G/C-->A/T transitions were linked to cytosine damage.
Conclusions:
- Gamma irradiation induces primarily mutagenic damage to guanine and cytosine in single-stranded M13 DNA.
- The observed mutation spectrum is consistent with specific types of DNA base damage and subsequent repair or replication errors.
- These findings differentiate the mutagenic outcomes of guanine versus cytosine damage following irradiation of single-stranded DNA.