This study focuses on gene expression of porcine circovirus (PCV) in order to identify viral genes and their corresponding mRNA transcripts. By northern blot analysis, the existence of three mRNAs could be demonstrated. Two mRNAs are encoded by the viral (-)-strand and one is encoded by the viral (+)-strand. The (+)-strand encoded mRNA transcript is 990 nucleotides (nt) long and corresponds to the open reading frame (ORF) 1, as shown by S1 mapping. The start point of this transcript is located at pos. 1238, as determined by primer extension analysis and rapid amplification of cDNA ends (RACE). The transcript is spliced as shown by direct reverse sequencing and RACE. It contains an untranslated "leader"-sequence 119 nt in size (pos. 1238 to 1120) which is joined to exon 2 of the ORF 1 transcript at pos. 737. The transcriptional regulatory elements have been identified functionally by CAT assays. They are located within a 258 base points (bp) fragment (pos. 1168 to 1425).