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Electron microscopic evidence for linear insertion of bacteriophage MU-1 in lysogenic bacteria
Abstract:
Temperate bacteriophage Mu-1 was used to generate a lysogenic derivative of the F'lac episome of Escherichia coli. Intact, covalently circular molecules of F'lac and lysogenic F'lac Mu(+) deoxyribonucleic acid (DNA) were isolated and examined by electron microscopy. The mean contour lengths of F'lac and F'lac Mu(+) molecules were 37.6 +/- 0.4 mum and 53.2 +/- 0.4 mum, respectively. The mean difference, 15.6 mum, is similar to the mean contour length of 12.9 +/- 0.1 mum obtained for linear DNA molecules released by osmotic shock from mature phage Mu-1 virions. These results provide direct physical evidence that phage Mu-1 integrates by linear insertion of its genome into the DNA of lysogenic host bacteria. Chemical and physical analyses of phage Mu-1 DNA indicate that it is similar to E. coli DNA in respect of gross base composition, buoyant density, and melting temperature.
Insights
Bacteriophage Mu-1 integrates into Escherichia coli DNA via linear insertion. Electron microscopy confirmed this integration mechanism by measuring DNA lengths of the F'lac episome and its Mu-1 lysogenic derivative.
Area of Science:
- Molecular Biology
- Microbiology
- Genetics
Background:
- Temperate bacteriophages, like Mu-1, can integrate their genetic material into host bacterial genomes.
- Lysogenic conversion involves the integration of phage DNA into the host's genetic material, altering its properties.
Purpose of the Study:
- To investigate the integration mechanism of temperate bacteriophage Mu-1 into the F'lac episome of Escherichia coli.
- To provide physical evidence for the mode of phage Mu-1 integration.
Main Methods:
- Generation of a lysogenic F'lac episome derivative using bacteriophage Mu-1.
- Isolation and examination of intact, covalently circular F'lac and lysogenic F'lac Mu(+) DNA molecules using electron microscopy.
- Measurement of DNA contour lengths and comparison with phage Mu-1 DNA length.
Main Results:
- Electron microscopy revealed a significant increase in the contour length of the F'lac Mu(+) DNA compared to the F'lac episome.
- The measured increase in DNA length corresponded to the length of the phage Mu-1 genome, suggesting insertion.
- Chemical and physical analyses showed phage Mu-1 DNA is similar to Escherichia coli DNA.
Conclusions:
- Phage Mu-1 integrates into the Escherichia coli F'lac episome by linear insertion of its genome.
- This study provides direct physical evidence supporting the linear insertion model for Mu-1 integration.
- Phage Mu-1 DNA shares biochemical similarities with host bacterial DNA.