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Category: Microbial Genetics and Molecular Biology
Plasmid Strategies for Broad-Host-Range Replication in Gram-Negative Bacteria, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555817732/9781555812652_Chap11-1.gif /docserver/preview/fulltext/10.1128/9781555817732/9781555812652_Chap11-2.gifAbstract:
This chapter emphasizes on the mechanisms that enable promiscuous plasmids of gram-negative bacteria to replicate in diverse hosts. Three different replication strategies have been identified thus far for circular plasmids: theta, strand displacement, and rolling circle. Each replication strategy has specific plasmid-directed initiation events leading to the establishment of the replisome and different host protein requirements. IncP plasmids can replicate in diverse gram-negative bacteria and can be conjugally transferred into an even broader group of organisms. Recent molecular studies have provided evidence that the mechanism utilized for recruitment of the host-encoded replicative helicase to the origin of plasmid RK2 is host specific and is dependent on the form of the TrfA protein present in the cell. Plasmids belonging to the IncQ group, including RSF1010 or R1162, are relatively small in size and have a moderate copy number. The final products of replication initiating at one of the two available ssi sites are a double-stranded replicated molecule and a single-stranded displaced circle. The studies with the IncQ plasmids reveal that providing the proteins essential for the establishment of the replisome allows sufficient flexibility for replication in different bacterial hosts. Recently an Escherichia coli mutant was isolated that allowed efficient replication of wild-type pPS10 at 37°C.
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Replicons of plasmids RK2 and RSF1010. The plasmid-encoded proteins and replication origin for plasmid RK2 (upper part) and RSF1010 (lower part) are as indicated. The map shown for RK2 spans from coordinates ∼18.2 to 12.1 kb of the published sequence (accession no. L27758). The map for RSF1010 spans from coordinates ∼2.1 to 7.6 kb of the published sequence (accession no. NC_001740). Not all of the proteins shown are essential for plasmid replication (see text for details). The origin of replication (oriV) has been expanded below the map for each plasmid to indicate the important features. For RK2 these features include eight 17-bp iterons (open arrows), four DnaA boxes (black arrowheads), AT-rich region (with 13-mcr sequences indicated by the small arrows), and GC-rich region. For plasmid RSF1010 the 20-bp iterons (open arrows indicating the three identical repeats and the dashed arrow indicating a fourth imperfect repeat), GC- and AT-rich regions, and the two ssi sires (arrows) are noted. For both plasmids the minimal origins and the direction of replication are as indicated.
Replicons of plasmids RK2 and RSF1010. The plasmid-encoded proteins and replication origin for plasmid RK2 (upper part) and RSF1010 (lower part) are as indicated. The map shown for RK2 spans from coordinates ∼18.2 to 12.1 kb of the published sequence (accession no. L27758). The map for RSF1010 spans from coordinates ∼2.1 to 7.6 kb of the published sequence (accession no. NC_001740). Not all of the proteins shown are essential for plasmid replication (see text for details). The origin of replication (oriV) has been expanded below the map for each plasmid to indicate the important features. For RK2 these features include eight 17-bp iterons (open arrows), four DnaA boxes (black arrowheads), AT-rich region (with 13-mcr sequences indicated by the small arrows), and GC-rich region. For plasmid RSF1010 the 20-bp iterons (open arrows indicating the three identical repeats and the dashed arrow indicating a fourth imperfect repeat), GC- and AT-rich regions, and the two ssi sires (arrows) are noted. For both plasmids the minimal origins and the direction of replication are as indicated.
Requirements for RK2 replication in E. coli and Pseudomonas species
Requirements for RK2 replication in E. coli and Pseudomonas species