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Mapping of RNA polymerase binding sites in R12 derived plasmids carrying the replication-incompatibility region and
Abstract:
Interactions between Escherichia coli RNA polymerase holoenzyme and three small plasmid DNAs (pSM1, pSM2, and pSM15) derived from the drug resistant factor R12 have been studied. These plasmids carry the copy number and incompatibility determinants, the origin of DNA replication and the rep gene(s) necessary for plasmid replication. They also contain the insertion element IS1 and the putative finO cistron. Thirteen DNA segments within the largest of the three plasmids (pSM2) were able to form either a binary and/or ternary complex with RNA polymerase. A unique strong binding site was mapped within the left end of IS1. Five binding sites were found within the rep-cop-inc region. Four of these are weak binding sites whereas the fifth does not form a stable binary complex and was detected by ternary complex formation. A strong binding site was located in the putative finO region whereas the remaining six binding sites are located in regions with unidentified genetic functions.
Insights
Researchers studied interactions between Escherichia coli RNA polymerase holoenzyme and R12 plasmid DNA. They identified thirteen binding sites on the pSM2 plasmid, including strong sites within IS1 and the finO region, crucial for plasmid function.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Plasmids are extrachromosomal DNA elements crucial for bacterial adaptation and antibiotic resistance.
- The R12 plasmid, a drug-resistant factor, harbors genes for replication (rep), copy number control, and incompatibility (inc).
- Escherichia coli RNA polymerase holoenzyme is central to gene transcription and DNA replication initiation.
Purpose of the Study:
- To investigate the binding interactions between Escherichia coli RNA polymerase holoenzyme and specific DNA segments of R12-derived plasmids.
- To map the locations and characterize the strengths of RNA polymerase binding sites on the pSM2 plasmid.
- To understand the role of these binding sites in plasmid replication and regulation.
Main Methods:
- Electrophoretic mobility shift assays (EMSA) to detect binary and ternary complex formation between RNA polymerase and plasmid DNA fragments.
- DNA footprinting techniques to precisely map binding sites.
- Analysis of plasmid DNA segments including IS1, rep-cop-inc regions, and the finO cistron.
Main Results:
- Thirteen distinct DNA segments on the pSM2 plasmid demonstrated binding with Escherichia coli RNA polymerase holoenzyme.
- A unique, strong RNA polymerase binding site was identified at the left end of the insertion sequence IS1.
- Multiple binding sites, including strong and weak interactions, were located within the rep-cop-inc region, essential for plasmid replication and control.
- A strong binding site was also found in the putative finO region, potentially involved in plasmid conjugation or stability.
- Six additional binding sites were identified in regions with currently unknown genetic functions.
Conclusions:
- Escherichia coli RNA polymerase holoenzyme interacts with multiple specific sites on R12-derived plasmids, suggesting regulatory roles beyond simple transcription initiation.
- The identified binding sites, particularly within IS1 and the rep-cop-inc region, are likely critical for the replication, copy number control, and stability of these plasmids.
- Further research is needed to elucidate the functions of the six newly identified binding sites in plasmid biology.