Podoviridae

Podoviridae
Virus classification
Group:	Group I (dsDNA)
Order:	Caudovirales
Family:	Podoviridae
Sub-families
	Autographivirinae; Picovirinae;

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

There are at least 74 species in this family.

Virology [edit]

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 and 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. Three internal proteins constitute the polymerase complex.

Two classes of genes are recognized (early and late). This classification is based on the timing of transcription that 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 [edit]

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.

Viral proteins accumulate in the cytoplasm and are associated with the periphery of the perinuclear space of the nucleoplasm. The capsid proteins associate with the viral DNA after being cut into size to form the provirion preformed capsids. The mature viruses assemble in the perinuclear space. They may also be found in the cytoplasm in crystalline arrays. The viruses are released from host cell by lysis.