PCV2 replicase transcripts in infected porcine kidney (PK15) cells

The Circoviridae family includes small viruses containing circular single strand DNA. There are two circoviruses described in pigs. Porcine Circovirus 2 (PCV2) has been linked to a disease termed Postweaning Multisystem Wasting Syndrome (PMWS) whereas a close relative of this virus, termed PCV type 1 (PCV1) has been considered a non-phatogenic contaminant of the PK15 cell line. Rolling circle replication of small DNA viruses like circoviruses is mediated by a replicase (Rep) gene that is transcribed into different mRNAs by an alternative splicing mechanism. In PCV1, two transcripts Rep and Rep' implicated in DNA replication, have been identified from infected cells. These transcripts are the product of a single gene with Rep' having a different carboxyl end than Rep. Sequence comparison shows that there is a high degree of homology for the Rep gene in both viruses. In this article, we have identified three different transcripts by RT-PCR in PCV2 infected PK15 cells. Two of them have homology with their PCV1 counterparts and the third transcript, termed Rep", corresponds to another spliced version of the Rep gene. This transcript, unique to PCV2, encodes for a protein of 80 amino acids in frame with the Rep sequence.