Summary: The sector of the genome of broad-host-range IncP plasmid RK2 from kb coordinate 54·0 to 60·0 confers an active partitioning phenotype, increasing the segregational stability of low-copy-number unstable plasmids. This Par region encodes the central control operon ( and ) and the associated genes and . Each ORF in this region was knocked out in turn and it was shown that only and are needed for the stability phenotype. encodes two polypeptides from alternative translational starts. A deletion of the start of the operon showed that only IncC2, the shorter product is essential for partitioning. Directed mutation or deletion was used to inactivate in turn each of the three KorB-binding sites (Os) which were candidate -acting sequences needed for stability. Only inactivation of O3, which lies between and , resulted in an increased rate of segregational loss. However, the rate of loss was significantly higher than the rate of loss of the test plasmid carrying none of this RK2 Par region. Either inactivation of or deletion of O1 from this O3 mutant resulted in restoration of the loss rate to that expected for the unstable test plasmid alone. Thus KorB can act on O1 to create a complex that either inhibits replication or reduces the effective plasmid copy number, perhaps by promoting pairing between plasmid molecules. This implies that RK2 goes through a cycle of pairing and separation, akin to the mitotic cycle of eukaryotic chromosomes.


Article metrics loading...

Loading full text...

Full text loading...


Most cited this month

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error