FIG. 6.

Model for RC replication. The plasmid-encoded Rep protein recognizes the dso on supercoiled DNA and introduces a site-specific nick generating a free 3′-OH end. This end is elongated by host proteins as the parental strand is being displaced. When the replication fork reaches the reconstituted dso, Rep protein catalyzes a strand transfer reaction, releasing an ssDNA intermediate and a dsDNA molecule with a parental and a newly synthesized (dotted) strand. Lagging-strand synthesis on the ssDNA molecule is initiated at the sso signal by the host RNA polymerase. This enzyme would synthesize a short primer RNA, and lagging-strand synthesis is performed by host DNA polymerases. The end products are supercoiled plasmid DNA molecules.