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Transfection of Escherichia coli spheroplasts with a bacteriophage Mu DNA-protein complex
Abstract:
We disrupted bacteriophage Mu particles by freeze-thaw treatment and recovered the DNA by CsCl density gradient centrifugation. This CsCl-purified DNA had a buoyant density which was indistinguishable from that of phenol-extracted Mu DNA. It was, however, 10(3) times more infective than phenol-extracted DNA for spheroplasts of exoV endI Escherichia coli. Infectivity was destroyed by proteinase K as well as by pancreatic DNase, indicating that the infective form was a DNA-protein complex. The infective properties of the complex demonstrated that the protein protects. Mu DNA against degradation by exonuclease V and that it serves at least one other function in bacteriophage Mu infection. The infectivity of the CsCl-purified DNA was due to a small class of highly infective molecules which sedimented 1.2. times faster than phenol-extracted Mu DNA on neutral sucrose gradients. This change in sedimentation rate is best explained by the formation of protein-linked circular monomers or linear dimers of Mu DNA. In vitro labeling of the DNA-protein complex, followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, showed that the CsCl-purified DNA contained a noncovalently associated 65,000-dalton polypeptide. A 65,000-dalton protein was also found to be a minor component of the bacteriophage Mu particle. No protein was found in phenol-extracted Mu DNA. These results suggest that the 65,000-dalton protein is necessary for successful phage infection and is normally injected into the host cell with the Mu genome.
Insights
A specific protein protects bacteriophage Mu DNA from degradation and aids infection. This protein is essential for phage infectivity and is delivered into the host cell with the Mu genome.
Area of Science:
- Molecular Biology
- Virology
- Genetics
Background:
- Bacteriophage Mu is a model organism for studying DNA replication and transposition.
- Understanding the molecular mechanisms of phage infection is crucial for developing novel therapeutic strategies.
- Previous studies have focused on the DNA component of bacteriophages, with less attention paid to associated proteins.
Purpose of the Study:
- To investigate the role of proteins associated with bacteriophage Mu DNA in infectivity.
- To identify the specific protein component responsible for protecting Mu DNA.
- To elucidate the function of this protein during the phage infection process.
Main Methods:
- Bacteriophage Mu particles were disrupted using freeze-thaw treatment.
- DNA was purified using CsCl density gradient centrifugation.
- Infectivity assays were performed on spheroplasts of Escherichia coli.
- DNA-protein complexes were analyzed using proteinase K, DNase, and gel electrophoresis.
Main Results:
- CsCl-purified Mu DNA was 1000 times more infective than phenol-extracted DNA.
- Infectivity was dependent on a DNA-protein complex, sensitive to proteinase K and DNase.
- A 65,000-dalton polypeptide was identified as a noncovalently associated component of the infective DNA.
- This protein protects Mu DNA from exonuclease V degradation and is a minor component of the phage particle.
Conclusions:
- A 65,000-dalton protein is essential for bacteriophage Mu DNA infectivity.
- This protein protects the Mu genome from host-encoded nucleases.
- The protein is likely injected into the host cell along with the Mu DNA, playing a critical role in infection initiation.