Siphoviridae
Siphoviridae is a family of double-stranded DNA viruses in the order Caudovirales. Bacteria and archaea serve as natural hosts. There are currently 313 species in this family, divided among 47 genera. The characteristic structural features of this family are a nonenveloped head and noncontractile tail.
Viruses in Siphoviridae are non-enveloped, with icosahedral and head-tail geometries (morphotype B1) or a prolate capsid (morphotype B2), and T=7 symmetry. The diameter is around 60 nm. Members of this family are also characterized by their filamentous, cross-banded, noncontractile tails, usually with short terminal and subterminal fibers. Genomes are double stranded and linear, around 50kb in length, containing about 70 genes. The guanine/cytosine content is usually around 52%.
Viral replication is cytoplasmic. Entry into the host cell is achieved by adsorption into the host cell. Replication follows the replicative transposition model. DNA-templated transcription is the method of transcription. Translation takes place by -1 ribosomal frameshifting, and +1 ribosomal frameshifting. The virus exits the host cell by lysis, and holin/endolysin/spanin proteins. Bacteria and archaea serve as the natural host. Transmission routes are passive diffusion.
Group: dsDNA
The organisation of genes in the genera L5likevirus, Lambdalikevirus, Phic3unalikevirus, and Psimunalikevirus and the proposed genera Sfi2likevirus, Sfi1likevirus, Sk1likevirus, and Tm4likevirus suggests that these may form a lambda supergroup (or subfamily).
The following genera have been proposed but are not currently ratified by the International Committee on Taxonomy of Viruses:
In addition to the above viruses, many members of Siphoviridae have been grouped into an unclassified group with no genus assignment. This group includes numerous phages known to infect Lactobacillus, Mycobacterium, , and other bacteria.
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