Plectrovirus
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''Plectrovirus'' is a genus of
virus A virus is a submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are ...
es, in the family '' Plectroviridae''. Bacteria in the phylum
Mycoplasmatota Mycoplasmatota is a phylum of bacteria that contains the class Mollicutes. The phylum was originally named "Tenericutes" (''tener cutis'': soft skin). Notable genera include '' Mycoplasma'', '' Spiroplasma'', '' Ureaplasma'', and ''Candidatus'' ...
serve as natural hosts, making these viruses
bacteriophage A bacteriophage (), also known informally as a phage (), is a virus that infects and replicates within bacteria. The term is derived . Bacteriophages are composed of proteins that Capsid, encapsulate a DNA or RNA genome, and may have structu ...
s. ''Acholeplasma virus L51'' is the only species in the genus.


Virology

The virons are non-enveloped and rod-shaped. 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 capsid protein); gp6, gp7 and gp8 (minor capsid 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 Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...
intermediate and the rolling circle mechanism. Gene transcription is by the host's cellular machinery each gene having a specific promoter.Melcher U, Comer J. 2011. Plectrovirus. In: The Springer Index of Viruses. Tidona, C & Darai, G, editors. Springer New York pp. 749–755.


Life cycle

There are six steps in the life cycle # Adsorption to the host via specific receptor(s) # Movement of the viral DNA into the host cell # Conversion of the single strand form to a double stranded intermediate # Replication of the viral genome # Synthesis of the new virons # Release of the new virons from the host A typical replication cycle normally take 10–15 minutes to complete.


Adsorption

This is mediated by one of the viral proteins (gp3) binding to the host receptor.


Entry into the host cell


Conversion to double stranded form

The conversion from single-stranded to double-stranded form is carried out by the host's own
DNA polymerase A DNA polymerase is a member of a family of enzymes that catalyze the synthesis of DNA molecules from nucleoside triphosphates, the molecular precursors of DNA. These enzymes are essential for DNA replication and usually work in groups to create t ...
. The host's
RNA polymerase In molecular biology, RNA polymerase (abbreviated RNAP or RNApol), or more specifically DNA-directed/dependent RNA polymerase (DdRP), is an enzyme that catalyzes the chemical reactions that synthesize RNA from a DNA template. Using the e ...
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
endonuclease In molecular biology, endonucleases are enzymes that cleave the phosphodiester bond within a polynucleotide chain (namely DNA or RNA). Some, such as deoxyribonuclease I, cut DNA relatively nonspecifically (with regard to sequence), while man ...
(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 gp1# 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 gp1# 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

Typically productive infection occurs by budding from the host membrane without
lysis Lysis ( ; from Greek 'loosening') is the breaking down of the membrane of a cell, often by viral, enzymic, or osmotic (that is, "lytic" ) mechanisms that compromise its integrity. A fluid containing the contents of lysed cells is called a ...
of the host.


Notes

A number of exceptions to this life cycle are known. Lysogenic species, which encode
integrase Retroviral integrase (IN) is an enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme ...
s, exist within this family.


References


External links


ICTV Report: ''Plectroviridae''


{{Taxonbar, from=Q7204418 Virus genera