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Journal of Virology, April 2004, p. 4268-4277, Vol. 78, No. 8
0022-538X/04/$08.00+0     DOI: 10.1128/JVI.78.8.4268-4277.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Detection of Template Strand Switching during Initiation and Termination of DNA Replication of Porcine Circovirus

Andrew K. Cheung*

Virus and Prion Diseases of Livestock Research Unit, National Animal Disease Center, USDA Agricultural Research Service, Ames, Iowa 50010

Received 23 September 2003/ Accepted 22 December 2003

Nucleotide substitution mutagenesis was conducted to investigate the importance of the inverted repeats (palindrome) at the origin of DNA replication (Ori) of porcine circovirus type 1 (PCV1). Viral genomes with engineered mutations on either arm or both arms of the palindrome were not impaired in protein synthesis and yielded infectious progeny viruses with restored or new palindromes. Thus, a flanking palindrome at the Ori was not essential for initiation of DNA replication, but one was generated inevitably at termination. Among the 26 viruses recovered, 16 showed evidence of template strand switching, from minus-strand genome DNA to palindromic strand DNA, during biosynthesis of the Ori. Here I propose a novel rolling-circle "melting-pot" model for PCV1 DNA replication. In this model, the replicator Rep protein complex binds, destabilizes, and nicks the Ori sequence to initiate leading-strand DNA synthesis. All four strands of the destabilized inverted repeats exist in a "melted" configuration, and the minus-strand viral genome and a palindromic strand are available as templates, simultaneously, during initiation or termination of DNA replication. Inherent in this model is a "gene correction" or "terminal repeat correction" mechanism that can restore mutilated inverted-repeat sequences to a palindrome at the Ori of circular DNAs or at the termini of circularized linear DNAs. Potentially, the melted state of the inverted repeats increases the rate of noncomplementary or illegitimate nucleotide incorporation into the palindrome. Thus, this melting-pot model provides insight into the mechanisms of DNA replication, gene correction, and illegitimate recombination at the Ori of PCV1, and it may be applicable to the replication of other circular DNA molecules.

* Mailing address: National Animal Disease Center, P.O. Box 70, Ames, IA 50010. Phone: (515) 663-7497. Fax: (515) 663-7458. E-mail: acheung{at}nadc.ars.usda.gov.

Journal of Virology, April 2004, p. 4268-4277, Vol. 78, No. 8
0022-538X/04/$08.00+0     DOI: 10.1128/JVI.78.8.4268-4277.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Guan, W., Wong, S., Zhi, N., Qiu, J. (2009). The Genome of Human Parvovirus B19 Can Replicate in Nonpermissive Cells with the Help of Adenovirus Genes and Produces Infectious Virus. J. Virol. 83: 9541-9553 [Abstract] [Full Text]  
  • Cheung, A. K. (2006). Rolling-Circle Replication of an Animal Circovirus Genome in a Theta-Replicating Bacterial Plasmid in Escherichia coli.. J. Virol. 80: 8686-8694 [Abstract] [Full Text]  
  • Steinfeldt, T., Finsterbusch, T., Mankertz, A. (2006). Demonstration of nicking/joining activity at the origin of DNA replication associated with the rep and rep' proteins of porcine circovirus type 1.. J. Virol. 80: 6225-6234 [Abstract] [Full Text]  
  • Cheung, A. K. (2004). Palindrome Regeneration by Template Strand-Switching Mechanism at the Origin of DNA Replication of Porcine Circovirus via the Rolling-Circle Melting-Pot Replication Model. J. Virol. 78: 9016-9029 [Abstract] [Full Text]  


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