Description of Podoviridae
adapted from
ICTVdb
Virion Properties
Morphology
Phages consist of a head
and a tail and are not enveloped. Phage has a head with
icosahedral symmetry and a tail with helical symmetry and
exhibits icosahedral symmetry (T=7). The head is isometric and
has a diameter of 60 nm. Head appear hexagonal in outline and
consists of 72 capsomers. The tail is straight, short and thick,
non-contractile rod built of stacked disks that is not banded and
has a length of 17 nm and a width of 6 nm. The tail has 6 short,
subterminal fibers.
Physicochemical and Physical Properties
The molecular mass (Mr) of
virions is about 48 x 10
6. Virions have a buoyant
density in CsCl of 1.44-1.51 g cm
-3. The sedimentation
coefficient is 510
S20w. Virions are not
sensitive to treatment with ether and chloroform.
Nucleic Acid
The Mr of the genome constitutes 50% of the virion
by weight. The genome is not segmented and contains a single
molecule of linear double-stranded DNA. The DNA is fully
sequenced. Complete sequence is 40000-42000 nucleotides long. The
genome has a guanine + cytosine content of 50 %. Double stranded
DNA is non-permuted. The genome has terminally redundant
sequences.
Proteins
Proteins constitute about 50% of the
particle weight.
The viral genome encodes structural proteins and
non-structural proteins. Virions consist of at least 9 structural
protein(s) located in the capsid.
Structural Proteins: Capsid protein head
protein. Capsid protein has a molecular mass of 38000 Da with 460
copies per virion.
Non-Structural Proteins: In addition to the
polymerase, the virus codes for enzymes such as adenylated
transferase (B type DNA polymerase and RNA polymerase) and 3
internal protein(s) located inside the head.
Lipids
Lipids are not reported.
Carbohydrates
Carbohydrates have not been
reported.
Genome Organization and Replication
Phages are adsorbed tail first to specific receptors
located on the cell wall and enter host cells by digestion with
lysozyme.
The process of intracellular uncoating of virions is
understood. Virus uncoating occurs in the cytoplasm.
Infection and
Replication: Although severity of illness depends on
route and dose, the majority of infections are virulent. Viral
DNA entering the nucleus remains linear. Infecting genome
integrates into the host genome. The host chromosome;
degenerates.
Transcription: The virus
codes for about 55 gene(s). Virus transcription is temporally
regulated; 2 classes of genes recognized; they are termed early
and late. Genes with related functions are clustered
together.
Translation: Genome
replication is bidirectional. During bidirectional replication
transcription phase DNA forms concatamers. Genome replication
occurs by a semi-conservative.
Replication cycle Viral
proteins accumulate in the cytoplasm; are associated with the
perinuclear space (periphery of nucleoplasm). Virions accumulate
in the cell cytoplasm.
Assembly and Egress:
Head proteins assemble with the viral DNA inside after genome has
been cut into size to form the provirions (preformed capsids).
Viruses assemble in the perinuclear space.
Maturation: In thin
sections the mature virus is can be seen in crystalline
arrays.
Release: Virus is
released from host cell upon death by lysis.