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Replication of plasmid DNA in Proteus mirabilis in limiting concentrations of thymine
Abstract:
Replicating forms of the R plasmid pRR12 and the colicin E1 plasmid RSF2124 were isolated from Proteus mirabilis after growth in medium containing a limiting concentration of thymine. Both plasmids were replicated as partially supercoiled intermediates, which have densities between the values of covalently closed circular and nicked circular plasmid DNA in ethidium bromide-cesium chloride gradients. In addition, both plasmids had replication intermediates, which have densities lower than that of linear P. mirabilis chromosomal DNA. Some structural features of these replication intermediates were examined.
Insights
Replication intermediates of R plasmid pRR12 and colicin E1 plasmid RSF2124 were observed in Proteus mirabilis grown with limited thymine. These intermediates exhibited unique densities, suggesting novel replication structures.
Area of Science:
- Molecular Biology
- Genetics
- Microbiology
Background:
- Plasmids are extrachromosomal DNA elements crucial for bacterial adaptation.
- Understanding plasmid replication mechanisms is vital for genetic engineering and combating antibiotic resistance.
- Previous studies have characterized various plasmid replication strategies.
Purpose of the Study:
- To investigate the replication intermediates of R plasmid pRR12 and colicin E1 plasmid RSF2124.
- To characterize the physical properties of these replication intermediates under specific growth conditions.
- To explore potential novel aspects of plasmid DNA replication.
Main Methods:
- Isolation of plasmids pRR12 and RSF2124 from Proteus mirabilis.
- Cultivation of bacteria in a medium with limited thymine concentration.
- Cesium chloride-ethidium bromide density gradient centrifugation to analyze plasmid DNA.
- Characterization of replication intermediates based on their buoyant density.
Main Results:
- Replication intermediates of both plasmids were successfully isolated.
- These intermediates displayed densities intermediate to covalently closed circular and nicked circular DNA.
- Replication intermediates showed lower densities than linear chromosomal DNA, indicating unique structural features.
Conclusions:
- Limited thymine availability influences plasmid replication in Proteus mirabilis.
- The observed replication intermediates suggest distinct structural conformations during replication.
- Further structural analysis is warranted to elucidate the precise mechanisms of these intermediates.