T7 phage

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"Gp5" redirects here. For other uses, see GP5.
Bacteriophage T7 Structural Model at Atomic Resolution[1]
Escherichia virus T7
Virus classification Edit this classification
(unranked): Virus
Realm: Duplodnaviria
Kingdom:
Heunggongvirae
Phylum: Uroviricota
Class: Caudoviricetes
Order: Caudovirales
Family: Autographiviridae
Genus: Teseptimavirus
Species:
Escherichia virus T7

Bacteriophage T7 (or the T7 phage) is a bacteriophage, a virus that infects bacteria. It infects most strains of Escherichia coli and relies on these hosts to propagate. Bacteriophage T7 has a lytic life cycle, meaning that it destroys the cell it infects. It also possesses several properties that make it an ideal phage for experimentation: its purification and concentration have produced consistent values in chemical analyses;[2] it can be rendered noninfectious by exposure to UV light;[3] and it can be used in phage display to clone RNA binding proteins.[3]

Discovery

In a 1945 study by Demerec and Fano,

Félix d'Herelle likely studied its close relative in the 1920s.[7][5]

Hosts

T7 grows on rough strains of Escherichia coli (i.e. those without full-length

enteric bacteria, but close relatives also infect smooth and even capsulated strains.[8] E. coli is more resistant to T7 than to some other similar phages.[citation needed
]

Virion structure

Colored microphotography of a T7 virion with its six tail fibers that are folded back against its capsid. The fibers extend as the virus locates a suitable host.
Annotated schematic drawing of a Enterobacteria phage T7 virion (cross section and side view)

The virus has complex structural symmetry, with a

nm and a tail 19 nm in diameter and 28.5 nm long attached to the capsid.[9] The ejection of proteins from the capsid upon infection causes the virus to change structure when it enters the cell.[10]

Genome

The

dsDNA genome which encodes 55 proteins.[13] The genome features numerous overlapping genes [14] that were partially removed through 'refactoring' the genome to produce T7.1.[15]

Schematic view of the phage T7 genome. Boxes are genes, numbers are gene numbers. Colors indicate functional groups as shown. White boxes are genes of unknown function or without annotation. Modified after [16]

Life cycle

T7 has a life cycle of 17 min at 37˚C, i.e. the time from infection to the lysis of the host cell when new phage are released. Due to the short latent period, most physiological studies are conducted at 30˚C where infected cells lyse after 30 min. However, high-fitness strains of T7 have been isolated with a latent period of only ~11 min at 37˚C growing under optimal conditions in rich media results. This adapted phage can undergo an effective expansion of its population by more than 1013 in one hour of growth.[17]

Infection of host bacteria

host cell
. Schematic drawing with annotations.
Tomograms of a T7 virion in action. T7 is using its fibers to "walk" across the cell surface and finally infect the cell.
Reproduction cycle of T7, in total
Replication machinery of T7, details

The T7 phage recognizes certain receptors on the surface of E.coli cells, and binds to the cell surface by its viral tail fibers. In some strains of T7, the tail fibers are replaced with tail-spikes that degrade the

enzymatic activity.[citation needed
]

The adsorbtion and penetration process use

peptidoglycan layer of the bacterial cell wall, allowing transfer of the viral DNA into the bacterium. The short, stubby tail of the T7-like phage is too short to span the cell envelope and, in order to eject the phage genome into the cell at the initiation of infection, virion proteins must first make a channel from the tip of the tail into the cell cytoplasm.[18]
The phage also releases five proteins needed to begin replication of the viral genome and cleave the host genome.[19] T7 bacteriophage has been evolved to override several of the host bacteria's defenses including the peptidoglycan cell wall and the CRISPR system.[19] Once the T7 phage has inserted the viral genome, the process of DNA replication of the host genome is halted and replication of viral genome begins.[citation needed]

Under optimal conditions, the T7 phage can complete the lytic process within 25 minutes, leading to the death of the E. coli host cell. At the time of lysis, the virus can produce over 100 progeny.[19]

Components

Gp5 (encoded by gene gp5) is T7 phage's

sliding DNA clamp during phage DNA replication (though thioredoxin normally has a different function). The sliding clamp functions to hold the polymerase onto the DNA, which increases the rate of synthesis.[20]

DNA replication and repair

Phage T7 has the simplest known DNA replisome, consisting of a helicase and primase that reside in a single polypeptide chain that forms a hexamer in the presence of DNA and ATP or dTTP. T7 DNA polymerase, assisted by E. coli thioredoxin, performs both leading and lagging-strand DNA synthesis.

In phage T7, DNA double-strand breaks are likely repaired by insertion of a patch of donor DNA into a gap at the break site.[21] This repair of double-strand breaks is facilitated by the gene 2.5 protein that promotes the annealing of homologous complementary strands of DNA.[22]

Replicative intermediates

The replicating intracellular DNA of phage T7, when stretched out after cell lysis, is usually longer than the mature phage chromosome (11 to 15 µM) and can occur in the form of highly concatenated linear strands up to 66 times the length of the mature phage chromosome.[23] The replicating DNA can also be seen in the form of coiled ring structures that appear to correspond to multiply looped DNA configurations in which superhelical twists, necessary for compaction of the DNA, were relieved by strand nicking upon cell lysis.[citation needed]

Applications in molecular biology

The T7 promoter sequence is used extensively in molecular biology due to its extremely high affinity for T7 RNA polymerase and thus high level of expression.[3][2]

T7 has been used as a model in

silent mutations
. T7 has been tested on human osteosarcoma to treat tumor cells.[citation needed]

References

  1. doi:10.5281/zenodo.5133295
    , retrieved 2021-07-24
  2. ^
    PMID 4902069
    .
  3. ^
    PMID 22230564
    , retrieved 2019-11-18
  4. PMID 17247150
    .
  5. ^
    ISBN 978-0-12-394788-8
    .
  6. ISBN 9780191727641
    .
  7. ^ d’Herelle, F. (1926). The Bacteriophage and Its Behavior. Baltimore, MD: Williams & Wilkins
  8. ^ Molineux, I. J. (2006). Chapter 20: The T7 group. In: The Bacteriophages (R. Calendar, ed.), pp. 277. Oxford University Press, Oxford.
  9. ^ "Teseptimavirus ~ ViralZone page". viralzone.expasy.org. Retrieved 2019-11-18.
  10. S2CID 205498472
    .
  11. ^ "Genome of bacteriophage T7". 9 September 2004. Retrieved 18 May 2011.
  12. PMID 6864790
    .
  13. ^ "Uniprot: reference proteome of bacteriophage T7".
  14. PMID 34611352
    .
  15. ^
    PMID 16729053
    .
  16. PMID 22748812
    .
  17. PMID 17598749
    .
  18. PMID 20036409
    .
  19. ^ a b c "New Details about Bacteriophage T7-Host Interactions". Archived from the original on 2011-08-17.
  20. PMID 10087914
    .
  21. PMID 10792729
  22. PMID 11222583
  23. ^ Bernstein C, Bernstein H. Coiled rings of DNA released from cells infected with bacteriophages T7 or T4 or from uninfected Escherichia coli. J Virol. 1974 Jun;13(6):1346-55. doi: 10.1128/JVI.13.6.1346-1355.1974. PMID 4598784; PMCID: PMC355455.

External links

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