Cystoviridae (taxid:10877)



Enveloped, spherical virion of 85 nm in diameter. The virion has a double capsid structure: the outer capsid has a T=13 icosahedral symmetry and the inner capsid has a T=2* icosahedral symmetry.
Virion maturation schemes



Segmented linear dsRNA genome. Contains 3 segments: Large (L), Medium (M) ans Small (S) coding for 12 proteins. Segments size range from 2.9 kb to 6.4 kb. Genome total size is 13.3 Kb.


Each segments encode for a polycystronic mRNA, translated into several proteins by the procaryotic translation machinery.




  1. There are two different attachment processes depending on the considered species. Multimeric protein P3 adsorb to host type IV pili which retracts bringing the virion in contact with the host membrane (e.g. Phi6). In other species, the attachment apparatus is a heteromeric protein assembly that utilizes the rough lipopolysaccharide as a receptor (e.g. Phi8, Phi12 or Phi13).
  2. Protein P6 mediates fusion of virus membrane with host outer membrane, releasing the capsid into the periplasmic space.
  3. The lytic enzyme P5 on the capsid surface digests the peptidoglycan layer of the host
  4. The capsid enters into the cytoplasm possibly via permeabilization of the host plasma membrane. Protein P8, which may be involved in this process, dissociates from the viral capsid. The rest of the capsid is released into the host cytoplasm.
  5. Genomic dsRNA remains enclosed by the inner capsid, thereby "hiding" from host antiviral mechanism.
  6. Polycystronic mRNA are transcribed by the viral RNA-dependent RNA polymerase (RdRp) P2 inside the core particle and released into the cell cytoplasm, so that dsRNA is never exposed to the cytoplasm. Full-length plus-strand transcripts from each of the dsRNA segments are synthesized. These plus-strand transcripts are used as templates for translation.
  7. Neo-synthesized proteins assemble into new capsids. The packaging NTPase P4 translocates the three ssRNA(+) genomic segments in the capsids where they are converted into dsRNA by the viral RdRp P2.
  8. The capsid is matured and enveloped in the cytoplasm.
  9. Mature virions are released from the cell by lysis.

Matching UniProtKB/Swiss-Prot entries

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13 entries grouped by strain

13 entries

Pseudomonas phage phi6 (Bacteriophage phi-6) reference strain

RDRP_BPPH6 RNA-directed RNA polymerase (EC (Protein P2)
EXLYS_BPPH6 Peptidoglycan hydrolase gp5 (Gene product 5) (Gp5)
P4_BPPH6 Packaging enzyme P4 (EC
P1_BPPH6 Major inner protein P1
FUS_BPPH6 Fusion protein P6
CAPSD_BPPH6 Major outer capsid protein (Protein P8)
P9_BPPH6 Major envelope protein (Protein P9)
P7_BPPH6 Assembly protein P7
P10_BPPH6 Envelope protein P10
P3_BPPH6 Spike protein P3
P12_BPPH6 Morphogenetic protein (Protein P12)
P13_BPPH6 Protein P13
P14_BPPH6 Protein P14