Escherichia virus T7

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Escherichia virus T7
Phage T7.png

Escherichia virus T7

Systematics
Classification : Viruses
Area : Duplodnaviria
Empire : Heunggongvirae
Phylum : Uroviricota
Class : Caudoviricetes
Order : Caudovirales
Family : Podoviridae
Subfamily : Autographivirinae
Genre : Teseptimavirus
Type : T7 phage
Taxonomic characteristics
Genome : dsDNA linear
Baltimore : Group 1
Symmetry : icosahedral, tailed
Scientific name
Escherichia virus T7
Short name
T7
Left
NCBI  Taxonomy: 1985738
NCBI  Reference: = 201850583 ICTV_Tax = 201850583

The bacteriophage T7 (or the T7 phage , officially Escherichia virus T7 ) is a virus species of the genus Teseptimavirus (formerly T7virus ) that infects susceptible bacterial cells. T7 phage have a double-stranded DNA - genome and most strains infect (English: strains ) of E. coli bacteria ( Escherichia coli ). The bacteriophage T7 has a lytic cycle and a number of properties that make it an ideal phage for experiments.

discovery

In a 1945 study by Demerec and Fano, T7 was described as one of seven phage types (T1 to T7) that infect coli bacteria. It is probably identical to the phage δ previously used by Delbrück. In addition, d'Herelle probably examined a close relative of T7 in the 1920s.

Hosts

T7 grows on 'rough' strains of Coli bacteria (i.e., those with no O-antigen full-length polysaccharide on their surface) and some other gut bacteria , but close relatives also infect smooth and even encapsulated strains.

construction

T7 virus particles (virions) have a complex structural symmetry. The capsid of the phage has an icosahedral head with an inner diameter of 55 nm, attached to a tail with a diameter of 19 nm and a length of 28.5 nm.

Genome

The genome of phage T7 is among the first fully sequenced genomes (published in 1983). The head of the virus particle contains the approximately 40 kbp double-stranded DNA genome which codes for 55 proteins .

Schematic view of the genome of a T7 phage. The sections correspond to genes and are marked with the gene number. The colors code the three functional groups shown, white boxes are genes with an unknown function or without annotation. Modified from Häuser et al. 2012. [11]

Propagation cycle

T7 has a short life cycle of 17 minutes (at 37 ° C), which is the time from infection to lysis (dissolution) of the host cell when the new phage virions are released. Due to the short latency period, most physiological studies are performed at a low 30 ° C, with infected cells then dissolving after 30 minutes. However, high fitness strains of T7 were isolated with a latency period of only approx. 11 min at 37 ° C. (under optimal conditions in enriched nutrient media).

Infection of the host cells

The T7 phage recognizes certain receptors on the surface of the coliform bacteria and adheres to the cell surface by virtue of its tail fibers; In some T7 strains, however, the tail fibers are replaced by tail tips ('spikes') with enzymatic activity that break down the O or K antigens on the cell surface. In the adsorption and penetration process, lysozymes are used to create an opening in the peptidoglycan layer of the bacterial cell wall , which then enables the viral DNA to be transferred into the bacterium.

Because of the short, stunted tail of the T7-like phage, proteins of the virion must first form a channel from the tip of the tail into the cell cytoplasm so that the phage genome can be injected into the cell at the beginning of the infection. The phage also injects proteins that are needed to start replicating the viral genome and fragment the host genome. The T7 bacteriophage overcomes various defense strategies of the host bacteria, in addition to the peptidoglycan cell wall, in particular the CRISPR system. As soon as the T7 phage has introduced its viral genome into the bacterium, the DNA replication process of the host genome is stopped and the replication of the viral genome begins. Under optimal conditions, the T7 phage can complete the entire process in 25 minutes with the dissolution (lysis) of the bacterium (i.e. death of the E. coli host cell), with the virus producing over 100 offspring.

Applications in molecular biology

The T7 promoter sequence is widely used in molecular biology because of its extremely high affinity for T7 RNA polymerase and the associated high level of expression.

T7 has been used as a model organism in synthetic biology . Chan et al. ' refactored ' the genome of T7 in 2005 , replacing approximately 12  kbp of its genome with synthesized DNA. The design of this engineered DNA was designed in such a way that it is easier to handle in several ways: Individual functional elements have been separated from one another (by a restriction endonuclease) for the purpose of simplified modification. In particular, overlapping protein-coding domains (coding sequences, i.e. 'genes' in the true sense) were separated. It was also investigated whether T7 or parts of it, possibly together with other components, could be suitable for the treatment of human tumor cells.

See also

Individual evidence

  1. ↑ a b c d ICTV: ICTV Taxonomy history: Enterobacteria phage T4 , EC 51, Berlin, Germany, July 2019; Email ratification March 2020 (MSL # 35)
  2. ↑ T7virus: Enterobacteria phage T7 , on: ViralZone , Swiss Institute of Bioinformatics (SIB)
  3. ↑ Master Species List 2018a v1 , on: ICTV online
  4. ↑ Demerec M, Fano U: Bacteriophage-Resistant Mutants in Escherichia Coli . In: Genetics . 30, No. 2, March 1945, pp. 119-136. PMID 17247150 . PMC 1209279 (free full text).
  5. ↑ a b Lobocka M, Szybalski (Ed.): Bacteriophages . Academic Press, December 31, 2012, ISBN 978-0-12-394788-8 , pp. 226 ff.
  6. ↑ d'Herelle, F. (1926). The Bacteriophage and Its Behavior. Baltimore, MD: Williams & Wilkins
  7. ^ Molineux, IJ (2006). Chapter 20: The T7 group. In: The Bacteriophages (R. Calendar, ed.), Pp. 277 ff, Oxford University Press, Oxford.
  8. ↑ Genome of bacteriophage T7 .
  9. ↑ JJ Dunn, FW Studier: Complete nucleotide sequence of bacteriophage T7 DNA and the locations of T7 genetic elements . In: Journal of Molecular Biology . 166, No. 4, 1983, pp. 477-535. doi : 10.1016 / S0022-2836 (83) 80282-4 . PMID 6864790 .
  10. ↑ Uniprot: reference proteome of bacteriophage T7 .
  11. ^ R. Hauser, S. Blasche, T. Dokland, E. Haggård-Ljungquist, A. von Brunn, M. Salas, S. Casjens, I. Molineux, P. Uetz: Bacteriophage protein-protein interactions (=  Advances in Virus Research, Vol. 83). 2012, ISBN 978-0-12-394438-2 , Bacteriophage Protein – Protein Interactions, p. 219–298 , doi : 10.1016 / B978-0-12-394438-2.00006-2 , PMID 22748812 , PMC 3461333 (free full text).
  12. ^ RH Heineman, JJ Bull: Testing Optimality with Experimental Evolution: Lysis Time in a Bacteriophage . In: evolution . 61, No. 7, 2007, pp. 1695-1709. doi : 10.1111 / j.1558-5646.2007.00132.x . PMID 17598749 . PMC 1974807 (free full text).
  13. ^ CY Chang, P. Kemp, IJ Molineux: Gp15 and gp16 cooperate in translocating bacteriophage T7 DNA into the infected cell . In: Virology . 398, No. 2, 2010, pp. 176-186. doi : 10.1016 / j.virol.2009.12.002 . PMID 20036409 . PMC 2825023 (free full text).
  14. ↑ a b c New Details about Bacteriophage T7-Host Interactions . Archived from the original on August 17, 2011.
  15. ↑ Chan LY, Kosuri S, Endy D: Refactoring bacteriophage T7 . In: Molecular Systems Biology . 1, 2005, p. 2005.0018. doi : 10.1038 / msb4100025 . PMID 16729053 . PMC 1681472 (free full text).
  16. ↑ Chen X, Li Y, Xiong K, Aizicovici S, Xie Y, Zhu Q, Sturtz F, Shulok J, Snodgrass R, Wagner TE, Platika D: Cancer gene therapy by direct tumor injections of a nonviral T7 vector encoding a thymidine kinase gene . In: Human Gene Therapy . 9, No. 5, March 1998, pp. 729-736. doi : 10.1089 / hum.1998.9.5-729 . PMID 9551620 .

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