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Location of an F-pilin pool in the inner membrane
Abstract:
Polyacrylamide gel analysis of [35S]methionine-labeled membrane preparations from Escherichia coli has revealed the presence of five polypeptides present only in the membranes of cells containing the conjugative plasmid F. In addition to the previously reported product of traT, polypeptides migrating with apparent molecular weights of 100,000, 23,500, 12,000, and 7,000 were resolved. Membrane preparations from F traJ mutants lacked these polypeptides, indicating that all of these proteins are tra gene products. The 7,000-molecular-weight polypeptide comigrated with unlabeled purified F-pilin protein. About 4 to 5% of the total radioactive label in whole membrane preparations was present in this polypeptide, indicating the existence of a substantial pool of membrane-associated F-pilin. The polypeptide could be extracted from whole membrane preparations with Triton X-100 and was found in the inner membrane fraction of membranes separated by sucrose density centrifugation.
Insights
Researchers identified five new proteins in Escherichia coli membranes linked to the conjugative plasmid F. One protein, F-pilin, is abundant and located in the inner membrane.
Area of Science:
- Molecular Biology
- Microbiology
- Genetics
Background:
- The conjugative plasmid F facilitates genetic exchange in bacteria like Escherichia coli.
- Understanding F plasmid-encoded proteins is crucial for bacterial conjugation research.
Purpose of the Study:
- To identify and characterize novel proteins associated with the conjugative plasmid F in Escherichia coli membranes.
- To investigate the role of tra genes in the expression of these membrane proteins.
Main Methods:
- [35S]methionine labeling of Escherichia coli membrane preparations.
- Polyacrylamide gel electrophoresis (PAGE) for polypeptide separation.
- Analysis of membrane preparations from wild-type and F traJ mutant strains.
- Sucrose density centrifugation to fractionate membrane components.
- Triton X-100 extraction to assess protein solubility and association.
Main Results:
- Five novel polypeptides were detected exclusively in membranes of F plasmid-containing E. coli.
- These polypeptides, including a 7,000-dalton protein, were absent in F traJ mutants, confirming they are tra gene products.
- The 7,000-dalton polypeptide co-migrated with purified F-pilin.
- F-pilin represented 4-5% of total membrane radioactivity, indicating a significant pool.
- F-pilin was extractable with Triton X-100 and localized to the inner membrane fraction.
Conclusions:
- The study identified several new F plasmid-encoded membrane proteins in E. coli.
- F-pilin is a major membrane-associated protein, predominantly located in the inner membrane.
- These findings contribute to understanding the molecular composition and organization of F plasmid-mediated conjugation machinery.