The ABCs of plasmid replication and segregation.

To ensure faithful transmission of low-copy plasmids to daughter cells, these plasmids must replicate once per cell cycle and distribute the replicated DNA to the nascent daughter cells. RepABC family plasmids are found exclusively in alphaproteobacteria and carry a combined replication and partitioning locus, the repABC cassette, which is also found on secondary chromosomes in this group. RepC and a replication origin are essential for plasmid replication, and RepA, RepB and the partitioning sites distribute the replicons to predivisional cells. Here, we review our current understanding of the transcriptional and post-transcriptional regulation of the Rep proteins and of their functions in plasmid replication and partitioning.