Submitted to: Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 15, 2002
Publication Date: September 5, 2003
Citation: Cheung, A.K. 2003. Transcriptional analysis of porcine circovirus type 2. Virology. 305(1):168-80. 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 this work, we examined PCV2 RNA biosynthesis in tissue culture cells. We identified several new PCV2 genetic elements that are different from the nonpathogenic PCV type 1. Thus, this work provides a general framework to elucidate the genetic basis for PCV2 pathogenicity and a method to screen for attenuated viruses for vaccine development.
Technical Abstract: The RNAs of porcine circovirus type 2 (PCV2) synthesized during productive infection in PK15 cells were characterized. A total of 6 RNAs were detected. They include the viral capsid protein RNA, a cluster of 4 Syn RNAs (designated Syn0, Syn1, Syn2a and Syn2b), and the NS RNA. NS is the most abundant RNA and it shares common 3' nucleotide sequence with the Syn RNAs. It is transcribed from a promoter present inside ORF1, independent from the Syn RNA promoter. Members of the Syn RNA cluster all share common 5' and 3' nucleotide sequences. Syn0, capable of coding for the replication associated protein (RepP), appears to be the primary transcript that give rises to Syn1, Syn2a and Syn2b by alternate splicing. Protein sequence alignment showed that Syn1 of PCV2 is equivalent to the Rep' of PCV1. Interestingly, the extensive amino acid homologous sequence observed between the deduced PCV RepP and the 2C-proteins of picornaviruses is not encoded by any of the spliced Syn RNAs. Contrary to a report which showed that the full-length Rep protein of PCV1 is required for PCV1 DNA replication, the full-length Rep encoded by Syn0 is not essential for PCV2 DNA replication. Therefore, whether Syn0 is translated to give a contiguous RepP or what role the Syn0 protein plays in the life cycle of porcine circoviruses is not clear at the present time.