RepE Monomer–Dimer Equilibrium Shapes Replication and Autoregulatory Control of the F Plasmid

Although the replication mechanism of the F plasmid and its regulatory strategies have been addressed in several studies, a comprehensive understanding of these processes remains incomplete. In this work, we present new observations that contribute to refining the current model of F plasmid replication control. In this work, the results indicate that plasmid copy number control in both the F plasmid and its derivatives is consistent with two previously proposed mechanisms: the titration model and the loop formation model. In both cases, the intracellular concentration and functional state of the RepE protein appear to play a central role. Consistent with earlier reports, the data of this study support the conclusion that the RepE monomer functions as the active replication initiator. Importantly, the transcriptional analyses suggest that not only RepE dimers but also monomers contribute to autoregulatory control of <i>rep</i>E expression. These findings support a model in which the monomer-dimer equilibrium of RepE shapes both replication initiation and transcriptional autoregulation of the F plasmid.