SEQUENCE OF PORCINE CIRCOVIRUS DNA - AFFINITIES WITH PLANT CIRCOVIRUSES

The complete nucleotide sequence (1759 nt) of the ssDNA genome of porc ine circovirus (PCV) was determined from a cloned dsDNA replicative fo rm isolated from PCV-infected cells, Sequence analysis detected no sig nificant nucleic acid or protein similarity with another animal circov irus, chicken anaemia virus (CAV) but, surprisingly, the highest prote in similarity was obtained between the product of the largest predicte d PCV ORF (ORF 1; encoding a potential protein of 357 kDa) and a putat ive protein encoded by the plant circovirus banana bunchy top virus (B BTV), High protein similarity was also detected with the other plant c ircoviruses subterranean clover stunt virus (SCSV) and coconut foliar decay virus (CFDV), This region of protein identity corresponds with t he 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 CFD V and SCSV and similar (one mismatch) to that found in the plant circo virus BBTV and in the geminiviruses, suggests that rolling-circle repl ication may operate during PCV DNA replication, These findings show th at PCV is unique in that it bridges the gap between animal and plant c ircoviruses, The taxonomic relationship of PCV with other members of t he Circoviridae is discussed.