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Outer membrane proteins of Escherichia coli. VI. Protein alteration in bacteriophage-resistant mutants
Abstract:
Protein 1 was shown to be the receptor for phage PA-2 by the observations that the purified protein inactivates the phage, mutants lacking the protein are resistant to the phage, and mutants selected for PA-2 resistance have altered protein. Protein 1 appears as two bands (1a and 1b) on high-resolution polyacrylamide gels. The most abundant classes of mutants (ParI and ParII) selected for PA-2 resistance were found to lack band 1b. The mutations responsible for the ParI and ParII phenotypes were mapped at a locus termed par, which is near nalA on the Escherichia coli chromosome. The cyanogen bromide peptides of proteins 1a and 1b are similar, suggesting that these bands represent modified forms of the same polypeptide. Strains carrying the tolF mutation produce only band 1b. When a par tolF double mutant was constructed, this strain produced only band 1a. These results suggest that genes at the par and tolF loci are involved in modification of protein 1, or regulation of such modification, and are not structural genes for protein 1.
Insights
Protein 1 is identified as the receptor for phage PA-2. Genetic analysis reveals that the par and tolF loci regulate modifications of Protein 1, rather than its structure.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Bacteriophage-host interactions are crucial in microbial ecology and evolution.
- Identifying specific phage receptors is key to understanding infection mechanisms.
Purpose of the Study:
- To identify the specific receptor for phage PA-2 on Escherichia coli.
- To elucidate the genetic basis of phage resistance and receptor modification.
Main Methods:
- Biochemical assays to test purified protein activity against phage PA-2.
- Isolation and characterization of phage-resistant mutants.
- Genetic mapping of resistance mutations.
- Analysis of protein expression using polyacrylamide gel electrophoresis.
Main Results:
- Purified Protein 1 inactivated phage PA-2; mutants lacking Protein 1 were resistant.
- Phage-resistant mutants (ParI, ParII) lacked Protein 1b, with mutations mapping to the par locus.
- Protein 1a and 1b share similar peptide maps, indicating they are modified forms of the same protein.
- The tolF mutation resulted in only Protein 1b, while a par tolF double mutant produced only Protein 1a.
Conclusions:
- Protein 1 serves as the receptor for phage PA-2.
- Genes at the par and tolF loci regulate the modification of Protein 1, not its synthesis.
- These findings provide insight into the molecular mechanisms of phage-host recognition and resistance.