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 repli cation of viral DNA. Truncation or introduction of point mutations into fou r conserved sequence motifs led to inactivation of Rep as replication initi ator. Transcription of rep starts at nucleotide 767 +/- 10 bp. An intron (n ucleotides 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 frames hift, 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 tr ansfected with a plasmid carrying the rep gene by real-time PCR. In contras t to other viruses replicating via a rolling circle, Rep protein alone cann ot promote replication: Rep and Rep' together comprise the functional repli cation initiator factor of PCV1. (C) 2001 Academic Press.