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Two replication initiation sites on R-plasmid DNA
Abstract:
Replicating DNA molecules of a deletion mutant of the conjugative R-plasmid R 6 K are cleaved at a single site by the EcoRI restriction endonuclease. Electron microscope examination and measurements of the EcoRI treated replicative intermediate molecules indicate that replication can be initiated at two sites on the plasmid DNA molecule. The two sites are located at about 23 and 39% of total length, respectively, from the EcoRI cleavage site. About 5% of the replicating molecules use both replication initiation sites simultaneously.
Insights
Replication of R 6 K plasmid DNA initiates at two distinct sites. Some molecules utilize both initiation sites simultaneously during replication.
Area of Science:
- Molecular Biology
- Genetics
- Microbiology
Background:
- The conjugative R-plasmid R 6 K is a key element in bacterial genetic exchange.
- Understanding plasmid replication mechanisms is crucial for molecular biology and genetics.
Purpose of the Study:
- To investigate the replication initiation sites of a deletion mutant of the R 6 K plasmid.
- To characterize the spatial and functional relationship of these initiation sites.
Main Methods:
- Cleavage of R 6 K plasmid DNA with EcoRI restriction endonuclease.
- Electron microscopy and molecular measurements of EcoRI-treated replicative intermediate molecules.
Main Results:
- Replicating R 6 K plasmid DNA molecules were cleaved at a single site by EcoRI.
- Replication initiation was found to occur at two specific sites on the plasmid DNA.
- These sites are located at approximately 23% and 39% of the total length from the EcoRI cleavage site.
- Approximately 5% of replicating molecules initiated replication from both sites concurrently.
Conclusions:
- The R 6 K plasmid possesses multiple, distinct replication origins.
- The simultaneous use of both initiation sites by a subset of molecules suggests complex regulatory mechanisms governing plasmid replication.