VIRION
Non-enveloped, head-tail structure. Heads are about 60 nm in diameter and tails 135 x 18 nm. The tail is contractile, has 6 long terminal fibers, 6 short spikes and a small base plate. The capsid has an elongated icosahedral symmetry T=7, composed of 72 capsomers (60 hexamers and 12 pentamers). Upon contraction, the tail sheath becomes loose and slides along the tail core.
GENOME
Linear, dsDNA genome of about 33 kb, encoding for about 45 proteins.
GENE EXPRESSION
Genes are transcribed by operons.
REPLICATION
CYTOPLASMIC
- Adsorption: the phage attaches to the target cell through its tail fibers.
- Viral exolysin degrades cell wall locally
- Ejection of the viral DNA into host cell cytoplasm by contraction of the tail sheath.
- Transcription and translation of early genes.
- Replication of genomic DNA by rolling circle. Linear molecules are generated from closed circular monomer product by viral terminase proteins.
- Transcription and translation of late genes.
- Assembly of an empty procapsid and packaging of the genome.
- Viral tail fibers assembly and viral tail assembly.
- Mature virions are released from the cell by lysis.