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Rolling circle replication produces multiple copies of a single circular template. Rolling circle replication ( RCR ) is a process of unidirectional nucleic acid replication that can rapidly synthesize multiple copies of circular molecules of DNA or RNA , such as plasmids , the genomes of bacteriophages , and the circular RNA genome of viroids .
This is accomplished by rolling circle replication with the Phi 29 DNA polymerase which binds and replicates the DNA template. The newly synthesized strand is released from the circular template, resulting in a long single-stranded DNA comprising several head-to-tail copies of the circular template. [10]
Rolling circle replication. When conjugation is initiated by a signal the relaxase enzyme creates a nick in one of the strands of the conjugative plasmid at the oriT. Relaxase may work alone or in a complex of over a dozen proteins known collectively as a relaxosome. In the F-plasmid system the relaxase enzyme is called TraI and the relaxosome ...
a: template, b: leading strand, c: lagging strand, d: replication fork, e: primer, f: Okazaki fragments Many enzymes are involved in the DNA replication fork. The replication fork is a structure that forms within the long helical DNA during DNA replication.
D-loop replication is a proposed process by which circular DNA like chloroplasts and mitochondria replicate their genetic material. An important component of understanding D-loop replication is that many chloroplasts and mitochondria have a single circular chromosome like bacteria instead of the linear chromosomes found in eukaryotes .
Concatemers are frequently the result of rolling circle replication, and may be seen in the late stage of infection of bacteria by phages. As an example, if the genes in the phage DNA are arranged ABC, then in a concatemer the genes would be ABCABCABCABC and so on (assuming synthesis was initiated between genes C and A).
Circular plasmids have been isolated and found in many different plants, with those in Vicia faba and Chenopodium album being the most studied and whose mechanism of replication is known. The circular plasmids can replicate using the θ model of replication (as in Vicia faba) and through rolling circle replication (as in C.album). [64]
The catenated circles require the action of topoisomerases to separate the circles (decatenation). In E. coli , DNA topoisomerase IV plays the major role in the separation of the catenated chromosomes, transiently breaking both DNA strands of one chromosome and allowing the other chromosome to pass through the break.