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Suppression of polar effects of nonsense mutations by ultraviolet irradiation
Abstract:
Nonsense mutations in capsid genes F and G of phages S13 and phi X174 decreased the expression of genes downstream. These polar effects were suppressed by ultraviolet irradiation of the host before infection. Activities of the downstream genes were restored to between 30 and 95% of their normal levels, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the viral proteins. The effect of ultraviolet irradiation may be to suppress rhodependent termination of transcription. The polarity of one mutation was poorly suppressed by ultraviolet irradiation.
Insights
Ultraviolet irradiation can restore gene expression in bacteriophages S13 and phi X174 following nonsense mutations. This process may involve suppressing transcription termination, though one mutation showed limited recovery.
Area of Science:
- Microbiology
- Molecular Biology
- Virology
Background:
- Bacteriophages S13 and phi X174 are double-stranded DNA viruses.
- Nonsense mutations can disrupt gene expression in a polar fashion.
- Polar effects in gene expression are often linked to transcription termination.
Purpose of the Study:
- To investigate the impact of nonsense mutations on downstream gene expression in phages S13 and phi X174.
- To determine the effect of ultraviolet (UV) irradiation on these polar effects.
- To elucidate the mechanism by which UV irradiation influences gene expression.
Main Methods:
- Induction of nonsense mutations in capsid genes F and G of phages S13 and phi X174.
- Infection of bacterial hosts with mutated phages.
- Treatment of host cells with UV irradiation prior to phage infection.
- Analysis of viral protein expression using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE).
Main Results:
- Nonsense mutations in capsid genes F and G caused decreased expression of downstream genes (polar effects).
- UV irradiation of host cells suppressed these polar effects, restoring downstream gene activity.
- Restored gene activities ranged from 30% to 95% of normal levels.
- One specific mutation exhibited poor suppression by UV irradiation.
Conclusions:
- UV irradiation can mitigate polar effects caused by nonsense mutations in phage gene expression.
- The mechanism likely involves the suppression of rho-dependent transcription termination.
- Phage gene expression regulation is sensitive to host cell conditions and DNA damage responses.