Submitted to: Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 18, 2003
Publication Date: September 1, 2003
Citation: CHEUNG, A.K. THE ESSENTIAL AND NON-ESSENTIAL TRANSCRIPTION UNITS FOR VIRAL PROTEIN SYNTHESIS AND DNA REPLICATION OF PORCINE CIRCOVIRUS TYPE 2. VIROLOGY. 2003. v. 313. p. 452-459. 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 PCV2 RNA biosynthesis in tissue culture cells and identified several new PCV2 genetic elements that are different from the non-pathogenic PCV type 1. In this work, we determined the essential and non-essential transcription units of PCV2 replication. Thus, this work provides a general frame work to elucidate the genetic basis for PCV2 pathogenicity and a method to screen for attenuated viruses for vaccine development.
Technical Abstract: During porcine circovirus (PCV) replication in PK15 cells, nine PCV type 2 (PCV2)-specific RNAs are synthesized. They include the capsid RNA (CR), five Rep-associated RNAs (Rep, Rep', Rep3a, Rep3b, Rep3c), and three NS-associated RNAs (NS515, NS672 and NS0). In this work, mutational studies were conducted to investigate the involvement of each PCV2 transcription unit in viral protein synthesis and DNA replication. The results demonstrated that a stop codon introduced at the very 5'-end of CR did not affect Rep-associated antigens or viral DNA synthesis. Altering the consensus dinucleotides at the splice junctions of the minor RNAs (Rep3a, Rep3b, Rep3c, NS515 and NS672) or introducing a stop codon in the abundant NS0 RNA also did not have any affect on viral protein synthesis or DNA replication. However, mutations that resulted in truncated Rep or Rep' proteins caused greater than 99% reduction of protein synthesis and complete shut down of viral DNA replication. These results demonstrated that both Rep and Rep' are absolutely essential for PCV2 replication.