AUTOREGULATION OF THE PARTITION GENES OF THE MINI-F PLASMID AND THE INTRACELLULAR-LOCALIZATION OF THEIR PRODUCTS IN ESCHERICHIA-COLI

The sopAB operon and the sopC sequence, which acts as a centromere, ar e essential for stable maintenance of the mini-F plasmid. Immunoprecip itation experiments with purified SopA and SopB proteins have demonstr ated that these proteins interact in vitro. Expression studies using t he lacZ gene as a reporter revealed that the sopAB operon is repressed by the cooperative action of SopA and SopB. Using immunofluorescence microscopy, we found discrete fluorescent foci of SopA and SopB in cel ls that produce both SopA and SopB in the presence of the sopC DNA seg ment, but not in the absence of sopC, suggesting the SopA-SopB complex binds to sopC segments. SopA was exclusively found to colocalize with nucleoids in cells that produced only SopA, while, in the absence of SopA, SopB was distributed in the cytosolic spaces.