T4 phage
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Model of the T4 phage |
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The T4 phage (officially Escherichia virus T4 , formerly Enterobacteria phage T4 bacteriophage T4 , T4 bacteriophage ) is a bacteriophage species in the genus T4virus (alias T4likevirus , T4-like viruses ) that infects Escherichia coli bacteria. With its morphology, it is considered the prototype of bacteriophages and was of great importance in virological research for understanding the propagation strategy of phages and viruses and general genetics (see also Hershey Chase experiment , Max Delbrück ). The species includes the subtypes T2, T4 and T6, so that the term T-even bacteriophages is also used in English (to be distinguished from the subfamily Tevenvirinae , which includes many more viruses).
structure
As a member of the order Caudovirales , family Myoviridae , genus Tequattrovirus (alias T4virus , T4likevirus ), the genome of the T4 phage consists of a single double-stranded DNA molecule with a length of 168,903 bp . It comprises about 300 genes and makes up 48% of the weight of the virion . The DNA contains, besides the normal nucleotides in place of cytosine the 5-hydroxymethylcytosine , additionally by a glucose residue glycosylated can be. This glycosylation of the DNA is probably responsible for the control of gene expression . The reading directions of the genome are circularly alternately reversed and there are redundant sections at the ends . Within the capsid , the DNA is regularly arranged according to a complex packing scheme.
The capsid of the T4 phage is basically icosahedral , but an elongated stretching that deviates from the basic shape is particularly typical for this species ( "elongated, pentagonal, bipyramidal antiprisms " ). It consists of 152 capsomeres and is about 111 nm long and 78 nm in diameter. Myoviridae have complex contractile tail pieces that consist of a neck piece (collar), a base plate, on which six short spikes and six long tail fibers attach. Overall, the tail piece is 113 × 16 nm in size with a molecular weight of about 2 × 10 7 Da from 430 polypeptide chains of 22 genes. During the replication of the T4 phage, a number of structurally unstable or non-DNA-packaging malformations (multiple capsids, non-stretched icosahedra) of the capsid arise, which is not surprising due to the highly complex structure. The virion consists of a total of 49 different proteins .
Eight serological subgroups of T4 phages can be distinguished by the different properties of antigen binding . Taxonomic subtypes of the species T4 phage are: Enterobacteria phage C16, F10, Fsα, PST, SKII, SKV, SKX, SV3, T2, T4 and T6 . The T2 phage (formerly a separate species) is therefore only a subtype of the T4 phage.
Infection cycle
The infection cycle lasts about 30 minutes. For this purpose, the phage docks with the ends of the tail fibers on porin proteins of the outer membrane of E. coli . The tail spine with a lysozyme function breaks through the cell wall enzymatically and the phage DNA is injected through the tail into the interior of the cell. There the DNA is first transcribed and translated by bacterial enzymes . The newly created phage polymerase now replicates the phage genes. During this time, the synthesis of the phage capsid begins. The replicated DNA is then packaged in this. Finally, phage-specific lysozyme is synthesized, which destroys the cell wall of the bacterium. This releases the mature phages.
particularities
The T4 phages have an extremely fast DNA synthesis apparatus, thanks to the viral DNA polymerase type B with an error rate of only one exchange for 300 genome copies. It has special DNA repair mechanisms that otherwise only occur in eukaryotic cells. This gives the T4 phage a high level of genetic stability despite the high replication rate.
In molecular biology and genetic engineering is the T4 DNA ligase of great importance, it is also just as T4 ligase called. Also, the T4 polynucleotide kinase , T4 RNA ligase and T4 DNA polymerase are important enzymes in molecular biology research.
literature
- ↑ a b c d ICTV: ICTV Taxonomy history: Enterobacteria phage T4 , EC 51, Berlin, Germany, July 2019; Email ratification March 2020 (MSL # 35)
- ↑ Myoviridae - dsDNA Viruses - dsDNA Viruses (2011). Retrieved August 7, 2019 .
- ↑ Petr G Leiman, Fumio Arisaka, Mark J van Raaij, Victor A Kostyuchenko, Anastasia A Aksyuk: Morphogenesis of the T4 tail and tail fibers . In: Virology Journal . tape 7 , no. December 1 , 2010, ISSN 1743-422X , doi : 10.1186 / 1743-422X-7-355 , PMID 21129200 , PMC 3004832 (free full text) - ( biomedcentral.com [accessed August 7, 2019]).
Further reading:
- CM Fauquet, MA Mayo et al: Eighth Report of the International Committee on Taxonomy of Viruses. Academic Press, Amsterdam et al. 2005, ISBN 0-12-249951-4 .
- J. Cairns, GS Stent, JD Watson (Eds.): Phage and the Origins of Molecular Biology. The Centennial Edition. CSHL Press, Cold Spring Harbor, NY, 2007, ISBN 978-0-87969-800-3 .
- G. Fuchs: General microbiology. 9th edition. Georg Thieme Verlag, Stuttgart 2014, ISBN 978-3-13-444609-8 .