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

5 entries

Pigeon circovirus (PiCV) (Columbid circovirus) reference strain

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

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

2 entries

Porcine circovirus 2 (PCV2)

ORF3_PCV2 Protein ORF3
ORF4_PCV2 Anti-apoptotic ORF4 protein