Transcriptional analysis of porcine circovirus type 2.

Porcine circovirus type 2 (PCV2) is the causative agent of an emerging swine disease, postweaning multisystemic wasting syndrome. In this work, the RNAs of PCV2 synthesized during productive infection in porcine kidney cells were characterized. A total of nine RNAs were detected. They include the viral capsid protein RNA (CR), a cluster of five Rep-associated RNAs (designated Rep, Rep', Rep3a, Rep3b, and Rep3c), and three NS-associated RNA (designated NS515, NS672, and NS0). Members of the Rep-associated RNA cluster all share common 5' and 3' nucleotide sequences and they also share 200 common 3' nucleotides with the NS-associated RNAs. Rep, capable of coding for the replication-associated-protein (RepP), appears to be the primary transcript that gives rise to Rep', Rep3a, Rep3b, and Rep3c by alternate splicing. Protein sequence alignment showed that RepP and the Rep' protein of PCV2 are equivalent to those described for PCV type 1 (PCV1) (a nonpathogenic virus), which had been shown to be essential for viral DNA replication. The results also suggest that NS515, NS672, and NS0 are transcribed from three different promoters inside ORF1 downstream of the Rep promoter. To date, only three RNAs (CR, Rep, and Rep') have been reported for PCV1-infected porcine kidney cells. Therefore, it is important to apply similar strategies from this study to reexamine the transcription pattern of PCV1.