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Replication of porcine circoviruses.

Faurez F, Dory D, Grasland B, Jestin A - Virol. J. (2009)

Bottom Line: Porcine circovirus type 1 is non pathogenic contrary to porcine circovirus type 2 which is associated with the disease known as Post-weaning Multisystemic Wasting Syndrome.Porcine circovirus replication probably involves a "melting pot" rather than "cruciform" rolling-circle mechanism.This review provides a summary of current knowledge of replication in porcine circoviruses as models of the Circovirus genus.Based on various studies, the factors affecting replication are defined and the mechanisms involved in the different phases of replication are described or proposed.

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Affiliation: French Food Safety Agency, Viral Genetics and Biosafety Unit, Ploufragan, France. f.faurez@afssa.fr

ABSTRACT
Porcine circoviruses are circular single-stranded DNA viruses that infect swine and wild boars. Two species of porcine circoviruses exist. Porcine circovirus type 1 is non pathogenic contrary to porcine circovirus type 2 which is associated with the disease known as Post-weaning Multisystemic Wasting Syndrome. Porcine circovirus DNA has been shown to replicate by a rolling circle mechanism. Other studies have revealed similar mechanisms of rolling-circle replication in plasmids and single-stranded viruses such as Geminivirus. Three elements are important in rolling-circle replication: i) a gene encoding initiator protein, ii) a double strand origin, and iii) a single strand origin. However, differences exist between viruses and plasmids and between viruses. Porcine circovirus replication probably involves a "melting pot" rather than "cruciform" rolling-circle mechanism.This review provides a summary of current knowledge of replication in porcine circoviruses as models of the Circovirus genus. Based on various studies, the factors affecting replication are defined and the mechanisms involved in the different phases of replication are described or proposed.

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Melting pot rolling circle replication model. i. Replication origin representation after binding of the Rep. Strands (+) and (-) are close together. The destabilized environment known as "melting pot" is included in the dotted oval. ii. Schematic representation of the template DNA strands during the initiation of DNA synthesis. The leading strand shifts strand 'a', and uses strands 'a' and 'b' as template DNA strands. iii. Schematic representation of the template DNA strands at the termination of DNA synthesis. The leading strand shifts strand 'b' and uses either the newly synthesized 'aN ' or strand 'b'. Black: positive polarized genome (+); Blue: negative strand; Red: potential base pairs representation. Reprinted from Journal of Virology 78(8), Cheung AK, "Detection of template strand switching during initiation and termination of DNA replication of porcine circovirus." pages 4268–4277, Copyright© 2004 [6], with permission from American Society for Microbiology.
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Figure 5: Melting pot rolling circle replication model. i. Replication origin representation after binding of the Rep. Strands (+) and (-) are close together. The destabilized environment known as "melting pot" is included in the dotted oval. ii. Schematic representation of the template DNA strands during the initiation of DNA synthesis. The leading strand shifts strand 'a', and uses strands 'a' and 'b' as template DNA strands. iii. Schematic representation of the template DNA strands at the termination of DNA synthesis. The leading strand shifts strand 'b' and uses either the newly synthesized 'aN ' or strand 'b'. Black: positive polarized genome (+); Blue: negative strand; Red: potential base pairs representation. Reprinted from Journal of Virology 78(8), Cheung AK, "Detection of template strand switching during initiation and termination of DNA replication of porcine circovirus." pages 4268–4277, Copyright© 2004 [6], with permission from American Society for Microbiology.

Mentions: Unlike the cruciform rolling-circle model of the Geminiviruses, PCVs exhibit "melting pot" organization [6]. This is described as a sphere of instability at the level of the stem-loop where the (+) and (-) strains are close together but not held by hydrogen bonds. This allows a possible exchange of matrix strand(s), also called template strand(s), during genome synthesis (figure 5). The rolling circle melting pot model, as defined by Cheung [6], was thoroughly investigated by Kato's team in 2003 [29]. This study revealed the ability of a quadruplet structure to generate transient triplex stem loop configurations, thereby making the two template strands available for positive strand synthesis and allowing easy exchange of these template strands. The availability of two template strands during synthesis of the leading strand seems to help maintain the nucleic sequence of the replication origin.


Replication of porcine circoviruses.

Faurez F, Dory D, Grasland B, Jestin A - Virol. J. (2009)

Melting pot rolling circle replication model. i. Replication origin representation after binding of the Rep. Strands (+) and (-) are close together. The destabilized environment known as "melting pot" is included in the dotted oval. ii. Schematic representation of the template DNA strands during the initiation of DNA synthesis. The leading strand shifts strand 'a', and uses strands 'a' and 'b' as template DNA strands. iii. Schematic representation of the template DNA strands at the termination of DNA synthesis. The leading strand shifts strand 'b' and uses either the newly synthesized 'aN ' or strand 'b'. Black: positive polarized genome (+); Blue: negative strand; Red: potential base pairs representation. Reprinted from Journal of Virology 78(8), Cheung AK, "Detection of template strand switching during initiation and termination of DNA replication of porcine circovirus." pages 4268–4277, Copyright© 2004 [6], with permission from American Society for Microbiology.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2690592&req=5

Figure 5: Melting pot rolling circle replication model. i. Replication origin representation after binding of the Rep. Strands (+) and (-) are close together. The destabilized environment known as "melting pot" is included in the dotted oval. ii. Schematic representation of the template DNA strands during the initiation of DNA synthesis. The leading strand shifts strand 'a', and uses strands 'a' and 'b' as template DNA strands. iii. Schematic representation of the template DNA strands at the termination of DNA synthesis. The leading strand shifts strand 'b' and uses either the newly synthesized 'aN ' or strand 'b'. Black: positive polarized genome (+); Blue: negative strand; Red: potential base pairs representation. Reprinted from Journal of Virology 78(8), Cheung AK, "Detection of template strand switching during initiation and termination of DNA replication of porcine circovirus." pages 4268–4277, Copyright© 2004 [6], with permission from American Society for Microbiology.
Mentions: Unlike the cruciform rolling-circle model of the Geminiviruses, PCVs exhibit "melting pot" organization [6]. This is described as a sphere of instability at the level of the stem-loop where the (+) and (-) strains are close together but not held by hydrogen bonds. This allows a possible exchange of matrix strand(s), also called template strand(s), during genome synthesis (figure 5). The rolling circle melting pot model, as defined by Cheung [6], was thoroughly investigated by Kato's team in 2003 [29]. This study revealed the ability of a quadruplet structure to generate transient triplex stem loop configurations, thereby making the two template strands available for positive strand synthesis and allowing easy exchange of these template strands. The availability of two template strands during synthesis of the leading strand seems to help maintain the nucleic sequence of the replication origin.

Bottom Line: Porcine circovirus type 1 is non pathogenic contrary to porcine circovirus type 2 which is associated with the disease known as Post-weaning Multisystemic Wasting Syndrome.Porcine circovirus replication probably involves a "melting pot" rather than "cruciform" rolling-circle mechanism.This review provides a summary of current knowledge of replication in porcine circoviruses as models of the Circovirus genus.Based on various studies, the factors affecting replication are defined and the mechanisms involved in the different phases of replication are described or proposed.

View Article: PubMed Central - HTML - PubMed

Affiliation: French Food Safety Agency, Viral Genetics and Biosafety Unit, Ploufragan, France. f.faurez@afssa.fr

ABSTRACT
Porcine circoviruses are circular single-stranded DNA viruses that infect swine and wild boars. Two species of porcine circoviruses exist. Porcine circovirus type 1 is non pathogenic contrary to porcine circovirus type 2 which is associated with the disease known as Post-weaning Multisystemic Wasting Syndrome. Porcine circovirus DNA has been shown to replicate by a rolling circle mechanism. Other studies have revealed similar mechanisms of rolling-circle replication in plasmids and single-stranded viruses such as Geminivirus. Three elements are important in rolling-circle replication: i) a gene encoding initiator protein, ii) a double strand origin, and iii) a single strand origin. However, differences exist between viruses and plasmids and between viruses. Porcine circovirus replication probably involves a "melting pot" rather than "cruciform" rolling-circle mechanism.This review provides a summary of current knowledge of replication in porcine circoviruses as models of the Circovirus genus. Based on various studies, the factors affecting replication are defined and the mechanisms involved in the different phases of replication are described or proposed.

Show MeSH
Related in: MedlinePlus