Submitted to: Journal of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/22/2003
Publication Date: 4/1/2004
Citation: Cheung, A.K. 2004. Detection of template strand-switching during initiation and termination of dna replication of porcine circovirus. Journal of Virology. 78(8):4268-4277. Interpretive Summary: Porcine circovirus type 2 (PCV2) is a newly emerged viral pathogen of swine. While clinical signs of disease and postmortem lesions induced by PCV2 are known, there is little information on the temporal pathogenesis and epidemiology of the virus. Because PCV2 was identified only recently, basic knowledge of the genetic and biochemical nature of the virus is limited. Standardized diagnostic tests have not developed and vaccines are not available. In previous work, we examined the genetic elements synthesized by PCV type 1 (PCV1) and PCV2 in tissue culture cells. We have identified several new PCV2 genetic elements that are different from the non-pathogenic PCV1 and have determined the essential and non-essential genetic elements required for PCV1 and PCV2 replication. In this work, we examined the mechanisms involved in PCV1 DNA synthesis and proposed a novel model to account for its replication. Thus, this work provides insight into the life-cycle of PCV and information that can be used to generate viruses for vaccine development.
Technical Abstract: The current rolling-circle replication (RCR) model for the synthesis of circular DNA molecules suggests that a "stem-loop" cruciform structure is formed at the origin of DNA replication (Ori), as the result of a replicator protein binding to its cognate recognition site and base-pairing of two flanking inverted repeat (palindrome) sequences. The general consensus is that this flanking palindrome is essential for DNA replication and only the palindromic strand serves as template for DNA synthesis at the Ori. In this report, I demonstrated that a palindrome is not essential for porcine circovirus RCR initiation; but one is generated inevitably, at termination. I proposed that the replicator protein-complex provides a "melting-pot" environment that destabilizes the double helix at the Ori and initiates new DNA polymerization, but there is no formation of a cruciform structure. Instead, all four strands of the inverted repeats exist in a "melted" configuration at the Ori and both the palindromic and the complementary strands can serve as templates for initiation and termination of leading-strand DNA synthesis.