Podoviridae_Virion
Podoviridae_Virion

The Podoviridae are a family of bacteriophages. Unlike the other families of tailed viruses this family has short tails that are non contractile.

There are at least 74 species in this family.
Virology

The viron is nonenveloped with a head-tail structure. There are 9 structural proteins.

The head is ~60 nanometers (nm) in diameter, consists of 72 capsomers and is icosahedral with a T = 7 symmetry. The head protein has a molecular mass of ~38 kiloDaltons and is present in 460 copies per virion.

The tail is non-contractile and has 6 short subterminal fibers. It is thick, rod-shaped and built of stacked disks. The maximum length is ~17 nm.

The double stranded DNA genome is linear ~40-42 kilobases in length and encodes ~55 genes. The guanine + cytosine content is ~50%. It has terminally redundant sequences and is nonpermuted. By weight the genome constitutes ~50% of the viron.

The genome encodes 9 structural proteins, an adenylated transferase B type DNA polymerase and an RNA polymerase. 3 internal proteins constitute the polymerase complex.

2 classes of genes are recognized (early and late). This classification is based on the timing of transcription which is temporally regulated. Genes with related functions are clustered together. Genome replication is bidirectional.

In general these viruses tend to be lytic rather than lysogenic.
Life cycle

Phages are adsorbed using tail first to specific receptors located on the cell wall and then enter host cells after digestion of the cell wall with lysozyme. Virus uncoating occurs in the cytoplasm. The viral DNA remains linear. In latent infections the infecting genome integrates into the host genome. Genome replication occurs by a semi-conservative mechanism. During replication the viral DNA forms concatamers. In lytic cycles the host genome degenerates.

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