Replication of porcine circovirus type 1 requires two proteins encoded by the viral rep gene

The rep gene of porcine circovirus type 1 (PCV1) is indispensable for replication of viral DNA. Truncation or introduction of point mutations into four conserved sequence motifs led to inactivation of Rep as replication initiator. Transcription of rep starts at nucleotide 767 +/- 10 bp. An intron (nucleotides 1176 to 1558) is removed by splicing. This leads to synthesis of a truncated protein, which was termed Rep' (19.2 kDa). Because of a frameshift, the last 48 amino acids of Rep' deviate from the C-terminus of the 35.6-kDa full-length Rep protein. The presence of full-length and spliced rep transcripts was demonstrated in PCV1-infected cells as well as in cells transfected with a plasmid carrying the rep gene by real-time PCR. In contrast to other viruses replicating via a rolling circle, Rep protein alone cannot promote replication: Rep and Rep' together comprise the functional replication initiator factor of PCV1. (C) 2001 Academic Press.