RCR (image) Arizona State University Share Print E-Mail Caption Rolling-circle replication is initiated by the Rep protein, which is encoded by a plasmid. It binds to the double-strand origin (DSO) of the plasmid. The protein then nicks one of the strands and remains bound to the 5' end of the nicked strand. The free 3' end is released to serve as a primer for DNA synthesis by DNA polymerase. Using the unnicked strand as a template, replication proceeds around the plasmid, (hence the name, rolling circle replication) displacing the nicked strand as single-stranded DNA. Once this single-stranded circle is complete, the 5' end which is attached to Rep and the displaced 3' end are joined in a chemical reaction. The double-stranded circle is closed as well when the DNA Polymerase returns to the DSO. Credit By Tobias Vornholt CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=39652309 Usage Restrictions None Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.