Spiromicrovirus (taxid:10852)



Non-enveloped, round, T=1 icosahedral symmetry, about 30 nm in diameter. The capsid consists of 12 pentagonal trumpet-shaped pentomers. The virion is composed of 60 copies each of the F, G, and J proteins, and 12 copies of the H protein. There are 12 spikes which are each composed of 5 G and one H proteins.



Circular, ssDNA(+) genome of 4.4 to 6.1kb. replication occurs via dsDNA intermediate and rolling circle.


Early and late genes promoters tightly regulate the timing of gene expression, which is crucial for the replication cycle.



  1. The viral particle attaches to host cell by binding host lipopolysaccharides.
  2. The proteins of the capsid perform Injection of the viral DNA through bacterial membranes into cell cytoplasm.
  3. Host polymerase convert the (+)ssDNA viral genome into a covalently closed dsDNA called replicative form DNA I (RF-I).
  4. Early viral genes are transcribed by host RNA polymerase, producing viral replication proteins.
  5. Viral protein A cleaves RF-I(+) DNA strand at the origin of replication and covalently attaches itself to the DNA.
  6. (+)strand replication occurs by rolling circle, which is converted to dsDNA by host polymerase, generating RF-II molecules (amplification of RF-I).
  7. Late viral genes are transcribed by host RNA polymerase.
  8. Procapsid assembly in the cytoplasm.
  9. Viral protein C binds to replication complex, inducing synthesis and packaging of neo-synthesized (+)ssDNA genomes (RF-III) into procapsids.
  10. Procapsids maturation occurs in host cytoplasm
  11. Mature virions are released from the cell by lysis.

Matching UniProtKB/Swiss-Prot entries

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9 entries grouped by strain

9 entries

Spiroplasma virus 4 (SpV4) reference strain

CAPSD_SPV4 Capsid protein VP1 (VP1)
REP_SPV4 Replication-associated protein ORF2 (EC 3.1.21.-) (EC (Rep)
H_SPV4 Minor spike protein H (H protein) (Pilot protein)
J_SPV4 DNA binding protein ORF8
B_SPV4 Internal scaffolding protein ORF3
C_SPV4 Protein ORF5
ORF6_SPV4 Uncharacterized protein ORF6
ORF7_SPV4 Uncharacterized protein ORF7
ORF9_SPV4 Uncharacterized protein ORF9