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Following Cell-fate in E. coli After Infection by Phage Lambda
Published on: October 14, 2011
Stability and instability in the lysogenic state of phage lambda.
John W Little1, Christine B Michalowski
1Department of Molecular and Cellular Biology, University of Arizona, Tucson, AZ 85721, USA. jlittle@u.arizona.edu
Journal of Bacteriology
|September 28, 2010
Summary
Bacteriophage lambda (λ) lysogenic state stability is surprisingly low. Intrinsic switching rates are minimal, suggesting evolution optimized stability under natural host SOS response conditions.
Area of Science:
- Molecular Biology
- Virology
- Genetics
Background:
- Gene regulatory circuits display emergent properties, including the stability of regulatory states.
- The lysogenic state of bacteriophage lambda (λ) involves viral repression by the CI repressor, but can switch to the lytic pathway upon host SOS system induction.
Purpose of the Study:
- To analyze the stability of the lysogenic state of phage λ.
- To investigate the intrinsic switching rates and the factors influencing lysogen stability.
- To characterize a mutant (λprm240) with altered stability for further study.
Main Methods:
- Measurement of intrinsic switching rates to the lytic pathway in a host lacking the SOS response.
- Analysis of a mutant (λprm240) with a weakened promoter for CI expression.
- Assessment of lysogen stability under different growth conditions (minimal vs. rich medium).
- Characterization of derivative mutants of λprm240 with modified stabilities.
Main Results:
- The intrinsic rate of switching to the lytic pathway in the absence of SOS response was extremely low (<10(-8)/generation).
- The stability of the λprm240 mutant was highly dependent on growth conditions, being stable in minimal medium but unstable in rich medium.
- These stability differences correlated with promoter strength variations observed in an uncoupled assay system.
Conclusions:
- The low intrinsic stability of phage λ lysogens may result from evolutionary optimization for switching under natural SOS-inducing conditions, rather than direct selection for intrinsic stability.
- The λprm240 mutant and its derivatives provide a valuable model system for dissecting the mechanisms underlying gene regulatory circuit stability and environmental influences.
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