Inoviridae
Encyclopedia
The Inoviridae are a family of filamentous bacteriophage
s. The name of the family is derived from the Greek
word 'nos' meaning 'muscle'.
There are five or more proteins in the capid: gp8 (the major capid protein); gp6, gp7 and gp8 (minor capid proteins); and gp3 which acts as the initial host binding protein.
The genomes are non segmented, circular, positive-sense, single-stranded DNA 4.4-8.5 kilobases in length. They encode 4 to 11 proteins.
Replication of the genome occurs via a dsDNA intermediate and the rolling circle mechanism.
Gene transcription is by the host's cellular machinery each gene having a specific promoter.
1. Adsorbion to the host via specific receptor(s)
2. Movement of the viral DNA into the host cell
3. Conversion of the single strand form to a double stranded intermediate
4. Replication of the viral genome
5. Synthesis of the new virons
6. Release of the new virons from the host
A typical replication cycle normally take 10-15 minutes to complete.
. The host's RNA polymerase
binds to the viral genome and syntheses RNA. Some of this RNA is translated and the remainder is used to initiate DNA replication.
(gp2) nicks the double stranded intermediate. This nicking site is specific and the sequence around the site highly symmetrical. The activity of gp2 is regulated by two other viral proteins: gp5 (single strand binding protein) and gp10. New viral genomes are produced via the rolling circle mechanism. These new single strand DNA sequences become templates for further DNA and RNA synthesis. When sufficient gp5 has accumulated within the cell, further DNA synthesis is halted and viron assembly begins.
while those of the genus Inovirus infect species of Enterobacteriaceae
, Pseudomonadaceae
, Spirillaceae
, Xanthomonadaceae
, Clostridium
and Propionibacterium
.
Bacteriophage
A bacteriophage is any one of a number of viruses that infect bacteria. They do this by injecting genetic material, which they carry enclosed in an outer protein capsid...
s. The name of the family is derived from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
word 'nos' meaning 'muscle'.
Virology
The virons are non enveloped, rod-shaped and filamentous. The capsid has a helical symmetry and is generally has a length of 85-280 nm or 760-1950 nm and a width of 10-16 nm or 6-8 nm respectively. These morphological differences depend on the species.There are five or more proteins in the capid: gp8 (the major capid protein); gp6, gp7 and gp8 (minor capid proteins); and gp3 which acts as the initial host binding protein.
The genomes are non segmented, circular, positive-sense, single-stranded DNA 4.4-8.5 kilobases in length. They encode 4 to 11 proteins.
Replication of the genome occurs via a dsDNA intermediate and the rolling circle mechanism.
Gene transcription is by the host's cellular machinery each gene having a specific promoter.
Life cycle
There are six steps in the life cycle1. Adsorbion to the host via specific receptor(s)
2. Movement of the viral DNA into the host cell
3. Conversion of the single strand form to a double stranded intermediate
4. Replication of the viral genome
5. Synthesis of the new virons
6. Release of the new virons from the host
A typical replication cycle normally take 10-15 minutes to complete.
Conversion to double stranded form
The conversion from single stranded to double stranded form is carried out by the host's own DNA polymeraseDNA polymerase
A DNA polymerase is an enzyme that helps catalyze in the polymerization of deoxyribonucleotides into a DNA strand. DNA polymerases are best known for their feedback role in DNA replication, in which the polymerase "reads" an intact DNA strand as a template and uses it to synthesize the new strand....
. The host's RNA polymerase
RNA polymerase
RNA polymerase is an enzyme that produces RNA. In cells, RNAP is needed for constructing RNA chains from DNA genes as templates, a process called transcription. RNA polymerase enzymes are essential to life and are found in all organisms and many viruses...
binds to the viral genome and syntheses RNA. Some of this RNA is translated and the remainder is used to initiate DNA replication.
Replication
This is initiated when a viral endonucleaseEndonuclease
Endonucleases are enzymes that cleave the phosphodiester bond within a polynucleotide chain, in contrast to exonucleases, which cleave phosphodiester bonds at the end of a polynucleotide chain. Typically, a restriction site will be a palindromic sequence four to six nucleotides long. Most...
(gp2) nicks the double stranded intermediate. This nicking site is specific and the sequence around the site highly symmetrical. The activity of gp2 is regulated by two other viral proteins: gp5 (single strand binding protein) and gp10. New viral genomes are produced via the rolling circle mechanism. These new single strand DNA sequences become templates for further DNA and RNA synthesis. When sufficient gp5 has accumulated within the cell, further DNA synthesis is halted and viron assembly begins.
Viron assembly
This is a complex process. It is initiated by the formation of a complex of gp1, gp7, gp9 and gp11 along with the single stranded DNA and gp%. It begins at a specific sequence within the DNA which is predicted to have a hairpin formation. Assembly continues at the membrane where ~1500 subunits of gp5 are displaced by ~2700 subunits of gp8 (the number of major capid protein subunits per viron). This process involves both gp1 and gp11. Assembly is completed by the addition of the viral proteins gp3 and gp6. In hosts with both an inner and outer membrane adhesion zones are created by gp4, a process that may also involve gp1.Viron release
This may involve host lysis but alternatively productive infection may occur by budding from the host membrane. This pattern is typically seen in the Plectivirus genus.Taxonomy
There are two genera in this family: Inovirus and Plectrovirus. These genera differ in their host range: the species in the Plectrovirus genus infect hosts of the class MollicutesMollicutes
The Mollicutes are a class of bacteria distinguished by the absence of a cell wall. The word "Mollicutes" is derived from the Latin mollis , and cutis . They are parasites of various animals and plants, living on or in the host's cells. Individuals are very small, typically only 0.2–0.3 μm in size...
while those of the genus Inovirus infect species of Enterobacteriaceae
Enterobacteriaceae
The Enterobacteriaceae is a large family of bacteria that includes many of the more familiar pathogens, such as Salmonella, Escherichia coli, Yersinia pestis, Klebsiella and Shigella. This family is the only representative in the order Enterobacteriales of the class Gammaproteobacteria in the...
, Pseudomonadaceae
Pseudomonadaceae
The Pseudomonadaceae is a family of bacteria that includes the genera Azomonas, Azomonotrichon, Azorhizophilus, Azotobacter, Cellvibrio, Mesophilobacter, Pseudomonas , Rhizobacter, Rugamonas, and Serpens...
, Spirillaceae
Spirillaceae
Spirillaceae is a family of bacteria. It has been described as a member of Nitrosomonadales, in Betaproteobacteria.It includes the species Spirillum minus which causes Rat bite fever....
, Xanthomonadaceae
Xanthomonadaceae
The Xanthomonadaceae are a family of Proteobacteria, given their own order....
, Clostridium
Clostridium
Clostridium is a genus of Gram-positive bacteria, belonging to the Firmicutes. They are obligate anaerobes capable of producing endospores. Individual cells are rod-shaped, which gives them their name, from the Greek kloster or spindle...
and Propionibacterium
Propionibacterium
Propionibacterium is a genus of bacteria named for their unique metabolism: They are able to synthesize propionic acid by using unusual transcarboxylase enzymes....
.