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Appropriate expression of filamentous phage f1 DNA replication genes II and X requires RNase E-dependent processing
1Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA.
Abstract:
The products of in-frame overlapping genes II and X carried by the filamentous phage f1 genome are proteins with required but opposing functions in phage DNA replication. Their normal relative levels are important for continuous production of phage DNA without killing infected Escherichia coli hosts. Here we identify several factors responsible for determining the relative levels of pII and pX and that, if perturbed, alter the normal distribution of the phage DNA species in infected hosts. Translation of the two proteins is essentially relegated to separate mRNAs. The mRNAs encoding genes II and X are also differentially sensitive to cleavage dependent on rne, the gene encoding the only E. coli endo-RNase known to have a global role in mRNA stability. Whereas pII levels are limited at the level of mRNA stability, normal pX levels require transcription in sufficient amounts from the promoter for the smaller mRNA encoding only pX.
Insights
Researchers identified factors controlling phage f1 gene II and X protein levels, crucial for balancing phage DNA replication and host survival. Perturbing these factors disrupts phage DNA distribution in Escherichia coli.
Area of Science:
- Molecular Biology
- Virology
- Genetics
Background:
- Filamentous phage f1 genome encodes overlapping genes II and X with opposing roles in DNA replication.
- Maintaining balanced expression of pII and pX proteins is vital for efficient phage DNA production and preventing host cell death.
Purpose of the Study:
- To identify factors regulating the relative expression levels of phage f1 pII and pX proteins.
- To investigate how alterations in these factors affect phage DNA species distribution within infected Escherichia coli.
Main Methods:
- Analysis of mRNA stability and translation regulation for genes II and X.
- Investigating the role of the E. coli endo-RNase (rne) in differential mRNA cleavage.
Main Results:
- Identified key factors influencing pII and pX protein ratios.
- Demonstrated that mRNA stability limits pII levels, while sufficient transcription from the smaller mRNA promoter is necessary for normal pX levels.
- Showed that perturbing these regulatory factors leads to altered phage DNA species distribution.
Conclusions:
- Differential mRNA processing and transcription control are critical for balancing pII and pX expression.
- Understanding these regulatory mechanisms provides insights into phage-host interactions and DNA replication strategies.
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