Enterobacteria phage T4

Enterobacteria phage T4
Virus classification
Group:	Group I (dsDNA)
Order:	Caudovirales
Family:	Myoviridae
Genus:	T4likeviruses
Species:	Enterobacteria phage T4

Enterobacteria phage T4 is a bacteriophage that infects Escherichia coli bacteria. The T4 phage is a member of the T-even phages, a group including enterobacteriophages T2 and T6. T4 is capable of undergoing only a lytic lifecycle and not the lysogenic lifecycle.

Genome and structure

The T4 phage's double-stranded DNA genome is about 169 kbp long and encodes 289 proteins. The T4 genome is terminally redundant and is first replicated as a unit, then several genomic units are recombined end-to-end to form a concatemer. When packaged, the concatemer is cut at unspecific positions of the same length, leading to several genomes that represent circular permutations of the original. The T4 genome bears eukaryote-like intron sequences.

Translation

The Shine-Dalgarno sequence GAGG dominates in bacteriophage T4 early genes, whereas the sequence GGAG is a target for the T4 endonuclease RegB that initiates the early mRNA degradation.

Virus particle structure

T4 is a relatively large phage, at approximately 90 nm wide and 200 nm long (most phages 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. The tail attaches to a host cell with the help of tail fibres. The tail fibres are also important in recognizing host cell surface receptors, so they determine if a bacterium is within the phage's host range.

Infection process

The T4 phage initiates an E. coli infection 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 phage can travel through the tail tube and enter the E. coli cell.

Life cycle

The lytic lifecycle (from entering a bacterium to its destruction) takes approximately 30 minutes (at 37 °C) and consists of:

• Adsorption and penetration (starting immediately)
• Arrest of host gene expression (starting immediately)
• Enzyme synthesis (starting after 5 minutes)
• DNA replication (starting after 10 minutes)
• 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 bacteriophage infect a host cell with their information and then blow up the host cell, thereby propagating themselves.

Replication and packaging

The rate of DNA replication in a living cell was first measured as the rate of phage T4 DNA elongation in phage-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 phage T4 DNA synthesis is 1.7 per 10⁸, a highly accurate DNA copying mechanism, with only 1 error in 300 copies. The phage also codes for unique DNA repair mechanisms. The T4 DNA packaging motor has been found to load DNA into phage 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.

History

The specific time and place of T4 phage isolation remains unclear, though they were likely found in sewage or fecal material. T4 and similar phages were described in a paper by Thomas F. Anderson, Max Delbrück, and Milislav Demerec in November 1944.

A number of Nobel Prize winners worked with phage T4 or T4-like phages including Max Delbrück, Salvador Luria, Alfred Hershey, James D. Watson, and Francis Crick. Other important scientists who worked with phage T4 include Michael Rossmann, Seymour Benzer, Bruce Alberts, Gisela Mosig, Richard Lenski, and James Bull.

See also

• T4 rII system

Further reading

• Leiman, P.G., Kanamaru, S., Mesyanzhinov, V.V., Arisaka, F., and Rossmann, M.G., "Structure and morphogenesis of bacteriophage T4."[1]
• Karam, J., Petrov, V., Nolan, J., Chin, D., Shatley, C., Krisch, H., and Letarov, A. The T4-like phages genome project. http://phage.bioc.tulane.edu/. (The T4-like phage full genomic sequence depository)
• 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) ISBN 0-19-514850-9
• (Indication of prevalence and T4-like phages in the wild)
• (Characterization of a T4-like phage)
• (Review of phage T4, from the perspective of its genome)
• (Overview of the RB49 genome, a T4-like phage)
• (T4 phage application in biotechnology for studying protein interaction)
• (Indication of the prevalence of T4-type sequences in the wild)
• (Historical description of the isolation of the T4-like phages T2, T4, and T6)
• (Nearly complete list of then-known T4-like phages)
• (Overview of various T4-like phages from the perspective of their genomes)
• (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) ISBN 1-55581-064-0
• 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) ISBN 0-914826-56-5
• 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)
• (rare type of translational regulation characterized in T4)
• (T4-like phage isolation, including that of phage Ox2)

External links

• Viralzone: T4-like viruses
• T4 Bacteriophage Infection Process Animations