Circovirus (taxid:39725)



Non-enveloped, round, T=1 icosahedral symmetry, about 17 nm in diameter. The capsid consists of 12 pentagonal trumpet-shaped pentamers.



Monopartite, circular, ssDNA genome of about 1800 to 2000bp.
The genome is replicated through double-stranded intermediates. The replication (Rep) protein initiates and terminates rolling circle replication, the host DNA polymerase being used for DNA replication itself. There is a potential stem-loop structure in the intergenic region that includes a conserved nonanucleotide sequence (AGTATTAC) where ssDNA synthesis is initiated.


The encapsidated viral DNA and the complementary DNA of the replicative intermediate encode two mRNAs for the Rep and capsid proteins.
Rep mRNA can undergo alternative splicing in some strains to produce Rep' protein.




  1. Virus penetrates into the host cell probably by clathrin- and caveolae-independent endocytosis.
  2. Uncoating, the viral ssDNA genome penetrates into the nucleus.
  3. Viral ssDNA is converted into dsDNA with the participation of cellular factors. dsDNA transcription gives rise to viral mRNAs.
  4. Viral mRNAs are translated to produce viral proteins.
  5. Replication may be mediated by a Rep protein, and would occur by rolling circle producing ssDNA genomes.
  6. These newly synthesized ssDNA can either
    a) be converted to dsDNA and serve as a template for transcription/replication
    b) be encapsidated by capsid protein and form virions released by cell lysis.

Host-virus interaction

Autophagy modulation

Cap protein of PCV2 induces activation of host autophagy in order to enhance its own replication .

Apoptosis modulation

PCV2 ORF3-encoded protein induces apoptosis by activating caspase-8 and caspase-3 pathways . This protein may be a candidate for PML bodies inhibition which is essential for nuclear virus replication in mammals.

Matching UniProtKB/Swiss-Prot entries

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25 entries grouped by strain

7 entries

Beak and feather disease virus (BFDV) reference strain

REP_BFDV Replication-associated protein (EC 2.7.7.-) (EC 3.1.21.-) (EC 3.6.1.-) (ATP-dependent helicase Rep) ...
CAPSD_BFDV Capsid protein
ORF4_BFDV Uncharacterized protein ORF4
ORF7_BFDV Uncharacterized protein ORF7
ORF6_BFDV Uncharacterized protein ORF6
ORF5_BFDV Uncharacterized protein ORF5
ORF3_BFDV Uncharacterized protein ORF3

3 entries

Porcine circovirus 2 (PCV2) reference strain

CAPSD_PCV2 Capsid protein
REP_PCV2 Replication-associated protein (EC 2.7.7.-) (EC 3.1.21.-) (EC 3.6.1.-) (ATP-dependent helicase Rep) ...
NS0_PCV2 Protein NS0

4 entries

Goose circovirus (GoCV) reference strain

REP_GOCV Replication-associated protein (EC 2.7.7.-) (EC 3.1.21.-) (EC 3.6.1.-) (ATP-dependent helicase Rep) ...
CAPSD_GOCV Probable capsid protein
ORFC2_GOCV Uncharacterized protein ORFC2
ORFV2_GOCV Uncharacterized protein ORFV2

2 entries

Canary circovirus (CaCV) reference strain

REP_CACV Replication-associated protein (EC 2.7.7.-) (EC 3.1.21.-) (EC 3.6.1.-) (ATP-dependent helicase Rep) ...
CAPSD_CACV Probable capsid protein

2 entries

Porcine circovirus 1 (PCV1) reference strain

REP_PCV1 Replication-associated protein (Rep) (EC 2.7.7.-) (EC 3.1.21.-) (EC 3.6.1.-) (ATP-dependent helicase ...
CAPSD_PCV1 Capsid protein

5 entries

Pigeon circovirus (PiCV) (Columbid circovirus)

REP_PICV Replication-associated protein (EC 2.7.7.-) (EC 3.1.21.-) (EC 3.6.1.-) (ATP-dependent helicase Rep) ...
CAPSD_PICV Probable capsid protein
ORFC3_PICV Uncharacterized protein ORFC3
ORFC4_PICV Uncharacterized protein ORFC4
ORFC2_PICV Uncharacterized protein ORFC2

2 entries

Porcine circovirus 2 (PCV2)

ORF3_PCV2 Protein ORF3
ORF4_PCV2 Anti-apoptotic ORF4 protein
These structures were created with the help of Colabfold by Jason Nomburg, Nathan Price and Jennifer Doudna (ModelArchive).

Acartia tonsa copepod circovirus taxid:1168547

Protein ModelArchive
Replication-associated protein (ATP-dependent helicase Rep) (RepP) ma-jd-viral-20901
Uncharacterized protein ma-jd-viral-49947

Anguilla anguilla circovirus taxid:1420600

Protein ModelArchive
Putative capsid protein ma-jd-viral-63316
Replication-associated protein (ATP-dependent helicase Rep) (RepP) ma-jd-viral-20702

Barbel circovirus taxid:759938

Protein ModelArchive
Putative capsid protein ma-jd-viral-27842
Replication-associated protein (ATP-dependent helicase Rep) (RepP) ma-jd-viral-20903

Canary circovirus taxid:142661

Protein ModelArchive
Probable capsid protein ma-jd-viral-28754
Replication-associated protein (EC 2.7.7.-) (EC 3.1.21.-) (EC 3.6.1.-) (ATP-dependent helicase Rep)... ma-jd-viral-20927

Canine circovirus taxid:1194757

Protein ModelArchive
Putative capsid protein ma-jd-viral-27432
Replication-associated protein (ATP-dependent helicase Rep) (RepP) ma-jd-viral-20747

Duck circovirus taxid:324685

Protein ModelArchive
Capsid protein ma-jd-viral-28851
Replication-associated protein (ATP-dependent helicase Rep) (RepP) ma-jd-viral-20938
Uncharacterized protein ma-jd-viral-57969
Uncharacterized protein ORFC2 ma-jd-viral-42269

Finch circovirus taxid:400122

Protein ModelArchive
Capsid protein ma-jd-viral-28761
Replication-associated protein (ATP-dependent helicase Rep) (RepP) ma-jd-viral-20866
Uncharacterized protein ma-jd-viral-58828

Goose circovirus taxid:146032

Protein ModelArchive
Probable capsid protein ma-jd-viral-28852
Replication-associated protein (EC 2.7.7.-) (EC 3.1.21.-) (EC 3.6.1.-) (ATP-dependent helicase Rep)... ma-jd-viral-20920
Uncharacterized protein ORFC2 ma-jd-viral-44063
Uncharacterized protein ORFV2 ma-jd-viral-34052

Gull circovirus taxid:400121

Protein ModelArchive
Capsid protein ma-jd-viral-28760
Replication-associated protein (ATP-dependent helicase Rep) (RepP) ma-jd-viral-20763
Uncharacterized protein ma-jd-viral-29081

Human circovirus VS6600022 taxid:1525173

Protein ModelArchive
Capsid protein ma-jd-viral-27904
Replication-associated protein (ATP-dependent helicase Rep) (RepP) ma-jd-viral-20967
Uncharacterized protein ma-jd-viral-53306
Uncharacterized protein ma-jd-viral-42295

Labidocera aestiva circovirus taxid:1173709

Protein ModelArchive
Putative structural protein ma-jd-viral-43922
Putative viral replication protein ma-jd-viral-20727

Mink circovirus taxid:1475143

Protein ModelArchive
Cap protein (Capsid protein) ma-jd-viral-27514
Replication-associated protein (ATP-dependent helicase Rep) (RepP) ma-jd-viral-20734

Penaeus monodon circovirus VN11 taxid:1419711

Protein ModelArchive
Nonstructural protein 2 ma-jd-viral-33106
Replication-associated protein ma-jd-viral-20894
Structural protein VP ma-jd-viral-28530

Pigeon circovirus taxid:126070

Protein ModelArchive
Probable capsid protein ma-jd-viral-28758
Replication-associated protein (EC 2.7.7.-) (EC 3.1.21.-) (EC 3.6.1.-) (ATP-dependent helicase Rep)... ma-jd-viral-20736
Uncharacterized protein ORFC2 ma-jd-viral-29716
Uncharacterized protein ORFC3 ma-jd-viral-63445
Uncharacterized protein ORFC4 ma-jd-viral-29225

Porcine circovirus 3 taxid:1868221

Protein ModelArchive
Cap ma-jd-viral-27790
Cap (Capsid) ma-jd-viral-27790

Porcine circovirus type 1/2a taxid:720569

Protein ModelArchive
Capsid ma-jd-viral-27508
Replication-associated protein (ATP-dependent helicase Rep) (RepP) ma-jd-viral-20701

Raven circovirus taxid:345250

Protein ModelArchive
Capsid protein ma-jd-viral-28759
Replication-associated protein (ATP-dependent helicase Rep) (RepP) ma-jd-viral-20758

Starling circovirus taxid:349370

Protein ModelArchive
Putative capsid protein ma-jd-viral-28753
Replication-associated protein (ATP-dependent helicase Rep) (RepP) ma-jd-viral-20809
Uncharacterized protein ma-jd-viral-39523

Swan circovirus taxid:459957

Protein ModelArchive
Putative capsid protein ma-jd-viral-28850
Replication-associated protein (ATP-dependent helicase Rep) (RepP) ma-jd-viral-20771

Zebra finch circovirus taxid:1642515

Protein ModelArchive
Capsid protein ma-jd-viral-28756
ORFC2 ma-jd-viral-29717
ORFV2 ma-jd-viral-42535
Replication-associated protein (ATP-dependent helicase Rep) (RepP) ma-jd-viral-20778