Submitted to: Journal of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2004
Publication Date: 9/1/2004
Citation: 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. Journal of Virology. 78(17):9016-9029. 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. 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. We also proposed a novel rolling circle "melting-pot" model to account for its replication based on substitution mutagenesis. In this work, we confirmed the "melting-pot" replication model by deletion mutagenesis. Thus, this work provides insight into the life-cycle of PCV and a general frame work to generate attenuated viruses.
Technical Abstract: Palindromic sequences (inverted repeats) flanking the origin of DNA replication (Ori) capable of forming single-stranded stem-loop structures (cruciform) have been reported to be essential for prokaryotic and eukaryotic DNA replication. In this study, input deletion genomes of porcine circovirus incapable of forming any stem-loop structures at the Ori invariably yielded progeny viruses containing longer and more stable palindromes. These results suggest that Ori-flanking palindromes are essential for termination but not for initiation of DNA replication. Detection of template-strand switching in the middle of an inverted repeat strand among the progeny viruses demonstrated that both the minus-genome and a corresponding palindromic strand served as templates simultaneously during DNA biosynthesis and supports the recently proposed rolling-circle "melting-pot" replication model. The genome configuration presented by this model is viable and it provides insights into the mechanisms of DNA replication, inverted repeats correction (or conversion) and illegitimate recombination of any circular DNA molecule with an Ori-flanking palindrome.