Divergence and conservation of the partitioning and global regulation functions in the central control region of the IncP plasmids RK2 and R751

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Abstract
Summary: The central control region (Ctl) of IncP plasmids is associated with two phenotypes: the coordinate expression of replication and transfer genes; and the ability to increase the segregational stability of a low-copy-number test plasmid. This region of the IncP plasmid R751 shows significant sequence divergence from the IncPα plasmid RK2 sequence, and two genes, korF and korG, present in the IncPα region are missing in the IncP Ctl. In other respects the organization of the Ctl is basically the same. Although the two key global regulatory genes korA and korB are highly conserved, studies on their ability to repress transcription from a variety of IncPα and IncP plasmid promoters suggest differences in operator recognition by KorA and synergy with other repressors. The products of kfrA, upf54.8 and upf54.4 genes are conserved; KfrA shows least conservation and, while retaining the ability to act as a transcriptional repressor, appears to have completely different DNA-binding specificity. The genes required for the plasmid segregational stabilization (partitioning) phenotype - incC, korB and the KorB operator OB3 - are conserved and contribute to a more efficient plasmid stabilization than the IncPα equivalents. This may indicate that the Ctl plays an especially important role in partitioning of IncP plasmids, since they lack the second stability region (parlmrs) found in IncP plasmids.
Funding Information
  • MRC Project (G9231237CB, G8919550CB)