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RepA and DnaA proteins are required for initiation of R1 plasmid replication in vitro and interact with the oriR
Abstract:
RepA, an initiation protein of R1 plasmid replication, was purified from an Escherichia coli strain overproducing the protein. The purified RepA protein specifically initiated replication in vitro of plasmid DNA bearing the replication origin of R1 plasmid (oriR). The replication, strictly dependent on added RepA protein, was independent of host RNA polymerase but required other host replication functions (DnaB and DnaC proteins, the single-stranded-DNA-binding protein SSB, and DNA gyrase). The replication was also completely dependent on the host DnaA function. In filter binding assays in high salt (0.5 M KCl) conditions, RepA specifically binds to both supercoiled and linear plasmid DNA containing the oriR sequence, whereas it binds to nonspecific DNA in low salt. DNase I-protection studies on a linearized DNA fragment revealed that DnaA protein specifically binds to a 9-base-pair DnaA-recognition sequence ("DnaA box") within oriR only when RepA is bound to the sequence immediately downstream of the DnaA box. These results indicate that initiation of R1 plasmid replication is triggered by interaction of RepA and DnaA proteins with the oriR sequence.
Insights
The R1 plasmid replication initiator protein, RepA, was purified and shown to initiate DNA replication in vitro. RepA and DnaA proteins interact with the R1 origin of replication (oriR) to trigger replication initiation.
Area of Science:
- Molecular Biology
- Microbiology
- Genetics
Background:
- R1 plasmid replication requires specific initiation proteins.
- Understanding the roles of these proteins is crucial for plasmid biology.
Purpose of the Study:
- To purify and characterize the RepA protein from R1 plasmid.
- To investigate the mechanism of R1 plasmid replication initiation in vitro.
Main Methods:
- Protein purification of RepA from Escherichia coli.
- In vitro replication assays using purified RepA and plasmid DNA.
- Filter binding assays and DNase I-protection studies to analyze protein-DNA interactions.
Main Results:
- Purified RepA initiated R1 plasmid replication in vitro, dependent on host replication factors (DnaB, DnaC, SSB, DNA gyrase) and DnaA.
- RepA specifically bound to the R1 origin of replication (oriR) sequence.
- DnaA protein binding to its recognition site within oriR was dependent on RepA binding.
Conclusions:
- RepA is a key initiation protein for R1 plasmid replication.
- Replication initiation is triggered by the coordinated interaction of RepA and DnaA proteins at the oriR sequence.