Replication proteins (rep) are involved in plasmid replication. The Rep protein binds to the plasmid DNA and nicks it at the double strand origin (dso) of replication. The 3'-hydroxyl end created is extended by the host DNA replicase, and the 5' end is displaced during synthesis. At the end of one replication round, Rep introduces a second single stranded break at the dso and ligates the ssDNA extremities generating one double-stranded plasmid and one circular ssDNA form. Complementary strand synthesis of the circular ssDNA is usually initiated at the single-stranded origin by the host RNA polymerase [1].

1: A rolling circle replication initiator protein with a nucleotidyl-transferase activity encoded by the plasmid pGT5 from the hyperthermophilic archaeon Pyrococcus abyssi. Marsin S, Forterre P; Mol Microbiol 1998;27:1183-1192. PMID:9570403