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Plasmid cointegrates of Flac and lambda prophage
Abstract:
Fifteen cointegrates of the plasmid Flac and prophage lambda that had suffered no detectable change in plasmid phenotype were isolated and characterized. The locations of the prophage insertions were determined by genetic analysis of deletion mutants obtained from each cointegrate as survivors of growth at 42 degrees C. In 11 cointegrates, the prophage was inserted between traI and lac, although probably in more than one location; in 3 others, it was on one side or the other of lac; and in 1 it was between lac and pif. Deletions covering all or part of the transfer region, as well as of lac and of pif, were obtained in the course of this analysis. Deletion mutants that had lost all known transfer genes were also oriT, but they retained the capacity to recircularize after transfer. Attempts were made to isolate lambda transducing phages for nearby plasmid genes from the cointegrates, and lambdaptraGD, lambdaptraD, lambdaptraI, and lambdadtraDI phages were obtained.
Insights
Researchers studied cointegrates of the plasmid Flac and prophage lambda, mapping insertion sites using genetic analysis. This revealed prophage lambda insertions in specific regions, aiding in the characterization of plasmid transfer genes.
Area of Science:
- Molecular Biology
- Genetics
- Microbiology
Background:
- Plasmids and bacteriophages are crucial genetic elements in bacteria.
- Understanding their interactions and genetic organization is key to molecular biology.
- Cointegrates, formed by the integration of plasmid and phage DNA, offer unique systems for genetic study.
Purpose of the Study:
- To characterize cointegrates formed between the F plasmid (Flac) and bacteriophage lambda.
- To determine the precise locations of prophage lambda insertions within the Flac plasmid.
- To analyze the genetic consequences of these insertions on plasmid phenotype and function.
Main Methods:
- Isolation and characterization of fifteen Flac-lambda cointegrates.
- Genetic analysis of deletion mutants derived from cointegrates.
- Determination of prophage insertion sites using temperature-sensitive selection (42°C).
- Isolation of lambda transducing phages carrying plasmid genes.
Main Results:
- Prophage lambda insertions were mapped to specific regions of the Flac plasmid.
- Eleven cointegrates showed prophage insertion between traI and lac.
- Three cointegrates had insertions flanking lac, and one between lac and pif.
- Deletions affecting transfer genes, lac, and pif were generated and analyzed.
- Deletion mutants lacking transfer genes retained the origin of transfer (oriT) and recircularization capacity.
- Specific lambda transducing phages (e.g., lambdaptraGD) were successfully isolated.
Conclusions:
- The genetic analysis successfully mapped prophage lambda insertion sites within Flac plasmid cointegrates.
- The study provided insights into the genetic organization and functional domains of the Flac plasmid, particularly the transfer region.
- The generated deletion mutants and transducing phages are valuable tools for further genetic studies of plasmid replication and transfer.