Department of Biotechnology
Rolling Circle Replication
A different pattern of DNA replication occurs during E. coli conjugation, a type of genetic
exchange mechanism observed in prokaryotes. The pattern is called rolling-circle replication, and
it also is observed during plasmid replication
and the reproduction of some viruses (e.g.,
phage lambda). Some eukaryotic viruses also
replicate their DNA or RNA via the rolling
circle mechanism.
Rolling circle replication describes a process of
unidirectional nucleic acid replication that can
rapidly synthesize multiple copies of circular
molecules of DNA or RNA. Rolling circle
DNA replication is initiated by an initiator
protein encoded by the plasmid or
bacteriophage DNA, which nicks one strand of
the double-stranded, circular DNA molecule at
a site called the double-strand origin, or DSO.
The initiator protein remains bound to the 5'
phosphate end of the nicked strand, and the free
3' hydroxyl end is released to serve as a primer
for DNA synthesis by DNA polymerase III.
Using the unnicked strand as a template,
replication proceeds around the circular DNA
molecule, displacing the nicked strand as
single-stranded DNA. Continued DNA
synthesis can produce multiple single-stranded
linear copies of the original DNA in a
continuous head-to-tail series called a
concatemer. These linear copies can be
converted to double-stranded circular
molecules. This mechanism is particularly
useful to viruses because it allows rapid,
continuous production of many genome copies
from a single initiation event.
Prepared by Nitin Swamy, Department of Biotechnology, SACJ
Department of Biotechnology
As a summary, a typical DNA rolling circle replication has five steps:
1. Circular dsDNA will be "nicked".
2. The 3' end is elongated using "unnicked" DNA as leading strand (template); 5' end is
displaced.
3. Displaced DNA is a lagging strand and is made double stranded via a series of Okazaki
fragments.
4. Replication of both "unnicked" and displaced ssDNA.
5. Displaced DNA circularizes.
Another representation of rolling circle model of replication..
Reference
• Microbiology:Prescott
• Genetics: a conceptual approach
• Wikipedia
Prepared by Nitin Swamy, Department of Biotechnology, SACJ
