Non-enveloped, head-tail structure. The capsid is about 84-94 nm in diameter and has a T=16 icosahedral symmetry (Spounalikevirus) . The tail is 140-219 in length, contractile with globular structures at its tip, has 6 long terminal fibers, 6 short spikes and a double base plate.


Linear, dsDNA genome of 130-160 kb, encoding for about 190-230 proteins. Some Twortlikevirus might have circularly permuted genomes.


Genes are transcribed by operons.



  1. Adsorption: the phage attaches to the target cell through its tail fibers.
  2. Ejection of the viral DNA into host cell cytoplasm by contraction of the tail sheath.
  3. Transcription and translation of early genes.
  4. Replication of viral DNA. Transcription and translation of late genes.
  5. Assembly of an empty procapsid and packaging of the genome.
  6. Viral tail fibers assembly and viral tail assembly.
  7. Mature virions are released from the cell by lysis.