Mini-F plasmid has three genes
sopA, sopB and
sopC essential for partitioning the plasmid. The
sopA and
sopB genes code for 43.7Kd and 35.4Kd proteins, respectively. The cis-acting
sopC region has twelve 43-bp direct repeats. Purified SopB protein binds to the
sopC DNA. SopA protein acts as the repressor of the
sopA-sopB operon in the presence of SopB protein. When plasmid-free segregants appear in cell division, they are killed postsegregationally by the ccd mechanism controlled by the
ccdA and
ccdB gene products of the plasmed.
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