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Inhibition of transcription starting from bacteriophage lambda pR promoter during the stringent response in
A Szalewska-Pałasz1, G Wegrzyn
1Department of Molecular Biology, University of Gdańsk, Poland.
Insights
Bacterial DNA replication halts under amino acid starvation in stringent strains but not relaxed mutants. This study shows reduced transcription from the lambda pR promoter causes this replication inhibition.
Area of Science:
- Molecular Biology
- Bacteriology
- Genetics
Background:
- Lambda plasmid DNA replication is regulated by transcriptional activation of the origin of replication (ori lambda).
- Bacterial responses to nutrient deprivation, such as the stringent response, significantly impact cellular processes, including DNA replication.
Purpose of the Study:
- To investigate the effect of the stringent response on lambda plasmid DNA replication in Escherichia coli.
- To determine the role of transcription from the lambda pR promoter in regulating replication during nutrient stress.
Main Methods:
- Utilized a lacZ gene fusion under the control of the bacteriophage lambda pR promoter to assess transcription levels.
- Quantified pR transcript levels using RNA-DNA hybridization.
Main Results:
- Transcription from the lambda pR promoter was inhibited in wild-type (stringent) E. coli during amino acid starvation.
- Replication of lambda plasmid DNA was halted in stringent strains but proceeded in relaxed mutants.
- pR promoter activity was not inhibited in relaxed mutants.
Conclusions:
- Decreased transcription from the pR promoter is responsible for the inhibition of lambda plasmid replication during the stringent response.
- Transcriptional activation of ori lambda is a key regulatory mechanism for lambda DNA replication under both normal and stringent growth conditions.
Abstract:
Replication of lambda plasmid DNA is halted in amino acid-starved wild type (stringent) strains whereas it proceeds in relA (relaxed) mutants. The only transcription which could be important in lambda plasmid DNA replication in amino acid-starved Escherichia coli cells is that starting from the pR promoter. Using a fusion which consists of the lacZ gene under the control of bacteriophage lambda pR promoter we found that transcription starting from this promoter was inhibited during the stringent, but not the relaxed, response in E. coli. We confirmed our conclusion by estimating the relative level of the pR transcript by RNA-DNA hybridization. We propose that decreased transcription from the pR promoter which serves as transcriptional activation of ori lambda is responsible for inhibition of lambda plasmid replication during the stringent response. The results presented in this paper, combined with our recent findings (published elsewhere), indicate that the transcriptional activation of ori lambda may be a main regulatory process controlling lambda DNA replication not only during the relaxed response but also in normal growth conditions.