Summary auto-generated
This study reports the complete nucleotide sequence (1759 bp) of porcine circovirus (PCV), a small animal circovirus with a circular single-stranded DNA genome. The researchers cloned and sequenced the PCV replicative form from persistently infected pig kidney cells, and the cloned DNA was confirmed to be infectious following transfection. Sequence analysis revealed surprising findings: while PCV showed little similarity to the animal circovirus chicken anaemia virus (CAV), it demonstrated significant protein homology with plant circoviruses, particularly banana bunchy top virus (BBTV), subterranean clover stunt virus (SCSV), and coconut foliar decay virus (CFDV). The largest predicted open reading frame (ORF1, encoding a ~36 kDa protein) showed homology to putative replication-associated proteins of plant circoviruses. Additionally, PCV contains a conserved nonanucleotide sequence within a stem-loop structure identical to that found in plant circoviruses and similar to geminivirus sequences, suggesting that rolling-circle replication may operate during PCV DNA replication. The authors concluded that PCV uniquely bridges animal and plant circoviruses, indicating possible common evolutionary origins and warranting taxonomic reassessment of circovirus classification.
Key findings
- PCV genome sequence is 1759 bp and contains seven open reading frames, with ORF1 (35.7 kDa) being the largest and only one large enough to encode the major structural protein
- PCV ORF1 protein shows highest homology to replication-associated proteins of plant circoviruses (BBTV, SCSV, CFDV) rather than to chicken anaemia virus (CAV), indicating closer evolutionary relationships with plant viruses
- PCV contains a conserved nonanucleotide motif (TAGTATTAC) within a stem-loop structure identical to plant circoviruses CFDV and SCSV, suggesting rolling-circle replication similar to geminiviruses
- Cloned PCV DNA is infectious following transfection into pig kidney cells, confirming the sequence integrity and functionality of the genome
- PCV uniquely bridges animal and plant circoviruses, suggesting common evolutionary pathways and warranting reconsideration of Circoviridae taxonomy
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Abstract
The complete nucleotide sequence (1759 nt) of the ssDNA genome of porcine circovirus (PCV) was determined from a cloned dsDNA replicative form isolated from PCV-infected cells. Sequence analysis detected no significant nucleic acid or protein similarity with another animal circovirus, chicken anaemia virus (CAV) but, surprisingly, the highest protein similarity was obtained between the product of the largest predicted PCV ORF (ORF1; encoding a potential protein of 35.7 kDa) and a putative protein encoded by the plant circovirus banana bunchy top virus (BBTV). High protein similarity was also detected with the other plant circoviruses subterranean clover stunt virus (SCSV) and coconut foliar decay virus (CFDV). This region of protein identity corresponds with the putative plant circovirus replication-associated protein (Rep). The presence of a nonanucleotide sequence at the apex of a potential-stem loop structure, identical to that found in the plant circoviruses CFDV and SCSV and similar (one mismatch) to that found in the plant circovirus BBTV and in the geminiviruses, suggests that rolling-circle replication may operate during PCV DNA replication. These findings show that PCV is unique in that it bridges the gap between animal and plant circoviruses. The taxonomic relationship of PCV with other members of the Circoviridae is discussed.