Related Experiment Videos
Role of CIS in replication of an IncB plasmid
1Department of Microbiology, University of Melbourne, Parkville, Victoria 3052, Australia.
Abstract:
Replication of the IncB plasmid pMU720 requires the synthesis of the cis-acting RepA protein and the presence of two DNA elements, ori and CIS. CIS is the 166-bp sequence separating the RepA coding sequence from ori. To investigate how this organization of the pMU720 replicon contributes to the mechanism of initiation of replication, mutations in the sequence and/or the length of CIS were introduced into the CIS region and their effects on the efficiency of replication of the pMU720 replicon in vivo was determined. The CIS region was found to be composed of two domains. The repA-proximal domain, which showed strong transcription termination activity, could be replaced by equivalent sequences from I-complex and IncL/M plasmids, whose replicons are organized in the same fashion as pMU720. Replacement by a trpA transcription terminator afforded only partial replication activity. The repA-distal domain was shown to be a spacer whose role was to position sequence(s) within ori on the correct face of the DNA helix vis-à-vis the repA-proximal portion of CIS. A model for the loading of RepA protein onto ori is discussed.
Insights
The IncB plasmid pMU720 replication requires the RepA protein and specific DNA elements. Mutations in the CIS region reveal its two domains are crucial for efficient plasmid replication initiation.
Area of Science:
- Molecular Biology
- Genetics
- Microbiology
Background:
- Plasmid replication is essential for bacterial survival and proliferation.
- The IncB plasmid pMU720 utilizes a cis-acting RepA protein and specific DNA elements (ori and CIS) for replication.
- Understanding plasmid replication mechanisms is key to developing novel genetic tools and antimicrobial strategies.
Purpose of the Study:
- To investigate the functional organization of the CIS region in the pMU720 replicon.
- To determine how sequence and length variations within CIS affect plasmid replication efficiency in vivo.
- To elucidate the roles of different CIS domains in the initiation of replication.
Main Methods:
- Site-directed mutagenesis was used to introduce sequence and length alterations into the CIS region of pMU720.
- Replication efficiency of mutant plasmids was assessed in vivo.
- Functional analysis of CIS domains by replacing them with heterologous sequences, including transcription terminators.
Main Results:
- The CIS region was delineated into two functional domains: a repA-proximal domain with strong transcription termination activity and a repA-distal domain acting as a spacer.
- The repA-proximal domain's transcription termination activity is conserved across different plasmid incompatibility groups (I-complex and IncL/M).
- The repA-distal domain's spacer function is critical for orienting ori sequences for proper RepA protein loading.
Conclusions:
- The CIS region's bipartite structure is essential for efficient pMU720 replication initiation.
- The repA-proximal domain ensures proper transcription termination, while the repA-distal domain positions ori elements for functional interaction with RepA.
- A model for RepA protein loading onto ori, mediated by the CIS region's organization, is proposed.