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Enterobacteria Phage T4
Species of bacteriophages that infect Escherichia coli
T4 is a relatively large virus, at approximately 90 nm wide and 200 nm long (most viruses range from 25 to 200 nm in length). The DNA genome is held in an icosahedral head, also known as a capsid. The T4's tail is hollow so that it can pass its nucleic acid into the cell it is infecting after attachment. Myoviridae phages like T4 have complex contractile tail structures with a large number of proteins involved in the tail assembly and function. The tail fibres are also important in recognizing host cell surface receptors, so they determine if a bacterium is within the virus's host range.
The structure of the 6 megadalton T4 baseplate that comprises 127 polypeptide chains of 13 different proteins (gene products 5, 5.4, 6, 7, 8, 9, 10, 11, 12, 25, 27, 48 and 53) has recently been described in atomic detail. An atomic model of the proximal region of the tail tube formed by gp54 and the main tube protein gp19 have also been created. The tape measure protein gp29 is present in the baseplate-tail tube complexes, but it could not be modeled.
The T4 virus initiates an Escherichia coliinfection by binding OmpC porin proteins and lipopolysaccharide (LPS) on the surface of E. coli cells with its long tail fibers (LTF). A recognition signal is sent through the LTFs to the baseplate. This unravels the short tail fibers (STF) that bind irreversibly to the E. coli cell surface. The baseplate changes conformation and the tail sheath contracts, causing GP5 at the end of the tail tube to puncture the outer membrane of the cell. The lysozyme domain of GP5 is activated and degrades the periplasmic peptidoglycan layer. The remaining part of the membrane is degraded and then DNA from the head of the virus can travel through the tail tube and enter the E. coli cell.
The lytic lifecycle (from entering a bacterium to its destruction) takes approximately 30 minutes (at 37 °C) and consists of:
Formation of new virus particles (starting after 12 minutes)
After the life cycle is complete, the host cell bursts open and ejects the newly built viruses into the environment, destroying the host cell. T4 has a burst size of approximately 100-150 viral particles per infected host. Complementation, deletion, and recombination tests can be used to map out the rII gene locus by using T4. These Escherichia viruses infect a host cell with their information and then blow up the host cell, thereby propagating themselves.
Replication and packaging
Virus T4 genome is synthesized within the host cell using Rolling Circle Replication.
The time it takes for DNA replication in a living cell was measured as the rate of virus T4 DNA elongation in virus-infected E. coli. During the period of exponential DNA increase at 37 °C, the rate was 749 nucleotides per second. The mutation rate per base pair per replication during virus T4 DNA synthesis is 1.7 per 10-8, a highly accurate DNA copying mechanism, with only 1 error in 300 copies. The virus also codes for unique DNA repair mechanisms. The T4 Phage head is assebled empty around a scaffolding protein, which is later degraded. Consequently the DNA needs to enter the prohead through a tiny pore, which is achieved by a hexamer of gp17 interactng with DNA first, which also serves as a motor and nuclease. The T4 DNA packaging motor has been found to load DNA into virus capsids at a rate up to 2000 base pairs per second. The power involved, if scaled up in size, would be equivalent to that of an average automobile engine.
Survival curves for virus T4 with DNA damaged by UV (top) or MMC (bottom) after single virus T4 infecting host cells (monocomplexes) or two or more virus T4 simultaneously infecting host cells (multicomplexes).
Multiplicity reactivation (MR) is the process by which two or more virus genomes, each containing inactivating genome damage, can interact within an infected cell to form a viable virus genome. Salvador Luria, while studying UV irradiated virus T4 in 1946, discovered MR and proposed that the observed reactivation of damaged virus occurs by a recombination mechanism.(see refs.) This preceded the confirmation of DNA as the genetic material in 1952 in related virus T2 by the Hershey-Chase experiment.
As remembered by Luria (1984, pg. 97) the discovery of reactivation of irradiated virus (referred to as "multiplicity reactivation") immediately started a flurry of activity in the study of repair of radiation damage within the early phage group (reviewed by Bernstein in 1981). It turned out later that the repair of damaged virus by mutual help that Luria had discovered was only one special case of DNA repair. Cells of all types, not just, bacteria and their viruses, but all organisms studied, including humans, are now known to have complex biochemical processes for repairing DNA damages (see DNA repair). DNA repair processes are also now recognized as playing critical roles in protecting against aging, cancer, and infertility.
MR is usually represented by "survival curves" where survival of plaque forming ability of multiply infected cells (multicomplexes) is plotted against dose of genome damaging agent. For comparison, the survival of virus plaque forming ability of singly infected cells (monocomplexes) is also plotted against dose of genome damaging agent. The top figure shows the survival curves for virus T4 multicomplexes and monocomplexes with increasing dose of UV light. Since survival is plotted on a log scale it is clear that survival of multicomplexes exceeds that of monocomplexes by very large factors (depending on dose). The UV inactivation curve for multicomplexes has an initial shoulder. Other virus T4 DNA damaging agents with shoulders in their multicomplex survival curves are X-rays and ethyl methane sulfonate (EMS). The presence of a shoulder has been interpreted to mean that two recombinational processes are used. The first one repairs DNA with high efficiency (in the "shoulder"), but is saturated in its ability as damage increases; the second pathway functions at all levels of damage. Surviving T4 virus released from multicomplexes show no increase in mutation, indicating that MR of UV irradiated virus is an accurate process.
The bottom figure shows the survival curves for inactivation of virus T4 by the DNA damaging agent mitomycin C (MMC). In this case the survival curve for multicomplexes has no initial shoulder, suggesting that only the second recombinational repair process described above is active. The efficiency of repair by this process is indicated by the observation that a dose of MMC that allows survival of only 1 in 1,000 monocomplexes allows survival of about 70% of multicomplexes. Similar multicomplex survival curves (without shoulders) were also obtained for the DNA damaging agents P32 decay, psoralen plus near-UV irradiation (PUVA), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), methyl methane sulfonate (MMS) and nitrous acid.
Several of the genes found to be necessary for MR in virus T4 proved to be orthologs for genes essential for recombination in prokaryotes, eukaryotes and archaea. This includes, for instance, T4 gene uvsX which specifies a protein that has three-dimensional structural homology to RecA from Escherichia coli and the homologous protein RAD51 in eukaryotes and RadA in archaea. It has been suggested that the efficient and accurate recombinational repair of DNA damages during MR may be analogous to the recombinational repair process that occurs during meiosis in eukaryotes.
The specific time and place of T4 virus isolation remains unclear, though they were likely found in sewage or fecal material. T4 and similar viruses were described in a paper by Thomas F. Anderson, Max Delbrück, and Milislav Demerec in November 1944.
^Taylor, Nicholas M. I.; Prokhorov, Nikolai S.; Guerrero-Ferreira, Ricardo C.; Shneider, Mikhail M.; Browning, Christopher; Goldie, Kenneth N.; Stahlberg, Henning; Leiman, Petr G. (2016). "Structure of the T4 baseplate and its function in triggering sheath contraction". Nature. 533 (7603): 346-352. Bibcode:2016Natur.533..346T. doi:10.1038/nature17971. PMID27193680.
Mosig, G., and F. Eiserling. 2006. T4 and related phages: structure and development, R. Calendar and S. T. Abedon (eds.), The Bacteriophages. Oxford University Press, Oxford. (Review of phage T4 biology)ISBN0-19-514850-9
Malys N, Chang DY, Baumann RG, Xie D, Black LW (2002). "A bipartite bacteriophage T4 SOC and HOC randomized peptide display library: detection and analysis of phage T4 terminase (gp17) and late sigma factor (gp55) interaction". J Mol Biol. 319 (2): 289-304. doi:10.1016/S0022-2836(02)00298-X. PMID12051907.(T4 phage application in biotechnology for studying protein interaction)
Monod C, Repoila F, Kutateladze M, Tétart F, Krisch HM (March 1997). "The genome of the pseudo T-even bacteriophages, a diverse group that resembles T4". J. Mol. Biol. 267 (2): 237-49. doi:10.1006/jmbi.1996.0867. PMID9096222.(Overview of various T4-like phages from the perspective of their genomes)
Kutter E.; Gachechiladze K.; Poglazov A.; Marusich E.; Shneider M.; Aronsson P.; Napuli A.; Porter D.; Mesyanzhinov V. (1995). "Evolution of T4-related phages". Virus Genes. 11 (2-3): 285-297. doi:10.1007/BF01728666. PMID8828153.(Comparison of the genomes of various T4-like phages)
Karam, J. D. et al. 1994. Molecular Biology of Bacteriophage T4. ASM Press, Washington, DC. (The second T4 bible, go here, as well as Mosig and Eiserling, 2006, to begin to learn about the biology T4 phage)ISBN1-55581-064-0
Eddy, S. R. 1992. Introns in the T-Even Bacteriophages. Ph.D. thesis. University of Colorado at Boulder. (Chapter 3 provides overview of various T4-like phages as well as the isolation of then-new T4-like phages)
Surdis, T.J "et al" Bacteriophage attachment methods specific to T4, analysis, Overview.
Mathews, C. K., E. M. Kutter, G. Mosig, and P. B. Berget. 1983. Bacteriophage T4. American Society for Microbiology, Washington, DC. (The first T4 bible; not all information here is duplicated in Karam et al., 1994; see especially the introductory chapter by Doermann for a historical overview of the T4-like phages)ISBN0-914826-56-5
Russell, R. L. 1967. Speciation Among the T-Even Bacteriophages. Ph.D. thesis. California Institute of Technology. (Isolation of the RB series of T4-like phages)
Malys N, Nivinskas R (2009). "Non-canonical RNA arrangement in T4-even phages: accommodated ribosome binding site at the gene 26-25 intercistronic junction". Mol Microbiol. 73 (6): 1115-1127. doi:10.1111/j.1365-2958.2009.06840.x. PMID19708923.(rare type of translational regulation characterized in T4)
Kay D.; Fildes P. (1962). "Hydroxymethylcytosine-containing and tryptophan-dependent bacteriophages isolated from city effluents". J. Gen. Microbiol. 27: 143-6. doi:10.1099/00221287-27-1-143. PMID14454648.(T4-like phage isolation, including that of phage Ox2)