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Origin and binding specificity of protein(s) coded for by Mu prophages
Abstract:
Crude extracts of bacteria lysogenic for temperature phage Mu contain proteins that retain specifically Mu DNA on nitrocellulose filters. The amount of binding protein is directly proportional to the number of Mu prophages per E. coli genome. Specificity of the binding reaction could be demonstrated by using heterologous DNAs as substrate and by a competition experiment. By using hybrid plasmids containing different amounts of the immunity end and extending to various degrees into MuDNA, it was found that the binding activity is coded for by the left 1,000 nucleotide-pair HindIII fragment. When using these hybrid plasmids as binding substrate, two different binding sites for the immunity product were detected. Joining of the MucI gene to the left lambda early promoter resulted in increased production of immunity protein at elevated temperature. A possible explanation for the relatively low amounts of immunity protein in all of the different strains studied is discussed.
Insights
Bacterial extracts contain proteins that bind specifically to Mu DNA, with binding levels correlating to Mu prophage presence. This immunity protein
Area of Science:
- Bacteriology
- Molecular Biology
- Genetics
Background:
- Bacteria lysogenic for bacteriophage Mu produce proteins that regulate phage gene expression.
- Understanding these regulatory proteins is crucial for controlling phage replication and lysogeny.
Purpose of the Study:
- To identify and characterize proteins from Mu-lysogenic bacteria that specifically bind Mu DNA.
- To determine the genetic basis and binding characteristics of the Mu immunity protein.
Main Methods:
- Nitrocellulose filter binding assays using crude bacterial extracts and Mu DNA.
- Competition experiments with heterologous DNA to assess binding specificity.
- Analysis of hybrid plasmids to map the gene encoding the binding activity.
Main Results:
- Proteins in crude bacterial extracts specifically retained Mu DNA on filters.
- Binding activity was directly proportional to the number of Mu prophages per genome.
- The binding activity was mapped to the left 1,000 nucleotide-pair HindIII fragment, identifying two binding sites.
- Increased immunity protein production was observed when the MucI gene was joined to the lambda early promoter.
Conclusions:
- A specific Mu DNA-binding protein, likely the immunity protein, was identified and characterized.
- The genetic locus for this binding activity was localized to a specific DNA fragment.
- Factors influencing the production levels of the immunity protein were investigated.