Identification of an octanucleotide motif sequence essential for viral protein, DNA, and progeny virus biosynthesis at the origin of DNA replication of porcine circovirus type 2.

A plasmid-based transfection system capable of generating infectious porcine circovirus type 2 (PCV2) was established. This system was then used in mutagenesis studies to investigate the involvement of a "conserved" nonanucleotide (which constitutes a portion of the loop sequence) located at the origin of DNA replication of PCV2 with respect to viral protein synthesis, DNA self-replication, and progeny virus production. The results demonstrated that an octanucleotide (AGTATTAC) embedded in the loop sequence is essential for virus replication. This octanucleotide can be further condensed to an essential core element (ECE) represented by AxTAxTAC. The positions specified by the indicated nucleotides are critical for viral DNA replication and stable infectious virus production, and they cannot be substituted by other bases, while the positions indicated by x can accept variable bases and yield stable progeny viruses.