Nucleotide Sequencing and Expression of Type 2 Porcine Circoviruses Isolated in Korea

ABSTRACT

Porcine circovirus (PCV) is a small, nonenveloped virus that contains a single-stranded circular DNA genome of about 1.76 Kb and belongs to the family Circoviridae. The PCV-2 was thought to be one of the causative agents for postweaning multisystemic wasting syndrome (PMWS) in pigs. In this study, the complete genome of two PCV-2 Korean isolates (KSY-1 and KSY-2) were sequenced and characterized. Also, the ORF2 gene of KSY-1 isolate was expressed in baculovirus expression system and the expressed protein was characterized. The sequence data indicated that the PCV-2 genome of two Korean isolates were 1,768 bases in length and encoded 2 major proteins, Rep (ORF1, 314 amino acids, 37 kDa) and a capsid (ORF2, 233 amino acids, 28~30 kDa) protein. There were 5 glycosylation sites and stem-loop structures with the nonanucleotide (5-AAGTATTAC-3), typically seen in PCV-2. Compared to nucleotide sequences of PCV-1 and PCV-2 reference strains, two Korean isolates were closely related; that is, they showed 98% homology in nucleotide sequence each other. Also, they showed 95~99% homology in nucleotide sequences with those of PCV-2 isolates but 76% similarity with those of PCV-1 reference strains. A phylogenetic analysis revealed that nucleotide sequences of Korean isolates were close to those of PCV-2 (AF055392) isolated in Canada. The baculovirusexpressed ORF2 migrated at 30 kDa and reacted with PCV-2 specific antiserum by indiect fluorescent antibody and Western blot analyses. It is concluded that our results could be valuable to understand the molecular characteristics of PCV-2 and to develop diagnostic methods for PCV-2 infections.