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A phase variation event that activates conjugation functions encoded by the Enterococcus faecalis plasmid pAD1.
1Department of Microbiology and Immunology, School of Medicine, University of Michigan, Ann Arbor 48109.
Plasmid
|November 1, 1991
Summary
Phase variation in Enterococcus faecalis (pAD1) allows for constitutive expression of plasmid transfer and aggregation functions. This pheromone-independent regulation provides an alternative mechanism for controlling plasmid transfer.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Enterococcus faecalis conjugation is regulated by sex pheromones like cAD1.
- Plasmid pAD1 mediates high-frequency transfer and aggregation in E. faecalis.
- Phenotypic changes include surface protein production and colony morphology shifts.
Purpose of the Study:
- Investigate the genetic basis of constitutive 'dry' colony variants (Dryc) in E. faecalis (pAD1).
- Determine the regulatory mechanisms underlying pheromone-independent plasmid transfer.
- Characterize the role of pAD1 regulatory regions in phase variation.
Main Methods:
- Isolation and characterization of spontaneous Dryc variants.
- Tn917-lac mutagenesis of pAD1 plasmid regions.
- Transcriptional analysis using lacZ fusions.
- Complementation tests for regulatory regions.
Main Results:
- Dryc variants constitutively express aggregation and plasmid transfer functions.
- Mutagenesis identified regulatory regions within pAD1 controlling cAD1 inducibility.
- Transcriptional analysis revealed constitutive expression in Dryc variants versus inducible in Dry+ cells.
- Phase variation of lacZ expression correlated with Dryc/Dry+ phenotypes.
Conclusions:
- The Dryc phenotype results from mutations within pAD1 regulatory regions.
- Phase variation provides a pheromone-independent mechanism for regulating pAD1 transfer.
- This study elucidates an alternative regulatory pathway for bacterial conjugation.