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First posted online 19 June 2000 ARTICLE ABSTRACT
Rec 13 March 2000; Acc 7 June 2000 DOI: 10.1099/vir.0.17035-0

Open reading frame 2 of porcine circovirus type 2 encodes a major capsid protein

Porntippa Nawagitgul,1 Igor Morozov,3 Steven R. Bolin,4 Perry A. Harms,2 Steven D. Sorden2 and Prem S. Paul1,2

1,2,3 Department of Veterinary Microbiology and Preventive Medicine1, Department of Veterinary Diagnostic and Production Animal Medicine2, and Veterinary Medical Research Institute (VMRI)3, Iowa State University, 1802 Elwood Drive, Bldg 6, Ames, IA 50011-1240, USA
4 Viral and Prion Diseases of Livestock Research Unit, National Animal Disease Center, ARS, USDA, Ames, Iowa, USA

Porcine circovirus 2 (PCV2), a single-stranded DNA virus associated with post-weaning multisystemic wasting syndrome of swine, has two potential open reading frames, ORF1 and ORF2, greater than 600 nucleotides in length. ORF1 is predicted to encode a replication-associated protein (Rep) essential for replication of viral DNA, while ORF2 contains a conserved basic amino acid sequence at the N terminus resembling that of the major structural protein of chicken anaemia virus. Thus far, the structural protein(s) of PCV2 have not been identified. In this study, a viral structural protein of 30 kDa was identified in purified PCV2 particles. ORF2 of PCV2 was cloned into a baculovirus expression vector and the gene product was expressed in insect cells. The expressed ORF2 gene product had a molecular mass of 30 kDa, similar to that detected in purified virus particles. The recombinant ORF2 protein self-assembled to form capsid-like particles when viewed by electron microscopy. Antibodies against the ORF2 protein were detected in samples of sera obtained from pigs as early as 3 weeks after experimental infection with PCV2. These results show that the major structural protein of PCV2 is encoded by ORF2 and has a molecular mass of 30 kDa.

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This article is now available in the September 2000 print issue of JGV (vol. 81, 2281-2287). The complete issue of the journal may be seen in electronic form on JGV Online.