Submitted to: Virology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/1/2004
Publication Date: 6/20/2004
Citation: Cheung, A.K. 2004. Identification of an octanucleotide motif sequence essential for viral protein, DNA, and progeny virus biosynthesis at the origin of DNA replication of porcine circovirus type 2. Virology. 324(1):28-36. 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 are 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 "melting-pot" model to account for its replication. In this work, we examined the mechanisms involved in PCV2 DNA replication and identified a signature DNA sequence that is essential for viral protein, DNA and progeny virus biosynthesis. Thus, this work provides insight into the life-cycle of PCV and a general frame work to generate attenuated viruses.
Technical Abstract: A plasmid-based transfection system capable of generating infectious porcine circovirus type 2 (PCV2) viruses was established. This system was then used in mutagenesis studies to investigate the involvement of the "loop-sequence", which is flanked by a pair of inverted repeats, located at the origin of DNA replication of PCV2 with respect to viral protein synthesis, DNA self-replication and progeny virus production. The results demonstrated that an octanucleotide (AGTATTAC) embedded in the loop-sequence is essential for virus replication. This octanucleotide can be further condensed to an essential core element represented by AxTAxTAC. The positions specified by the indicated nucleotides are critical for viral DNA replication and stable infectious virus production and they cannot be substituted by other bases, while the positions indicated by x can accept variable bases and yield stable progeny viruses.