Enterobacteria phage T2

  Enterobacteria phage T2 is a virulent bacteriophage of the T4-like viruses genus, in the family Myoviridae. It infects Eschericia coli and is the best known of the T-even phages. Its virion contains linear double-stranded DNA, terminally redundant and circularly permuted. The phage is covered by a protective protein coat, which normally contains sulfur. In addition, the only molecule in the phage that contains phosphorus is its DNA.

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This phage can quickly turn an E. coli cell into a T2-producing factory that releases phages when the cell ruptures. Experiments conducted by Alfred Hershey and Martha Chase displayed that the DNA of viruses is injected into the bacterial cells, while most of the viral proteins remain outside. The injected DNA molecules cause the bacterial cells to produce more viral DNA and proteins. These discoveries supported that DNA, rather than proteins, is the hereditary material.

The first phages that were studied in detail included seven that commonly infect E. coli. They were named Type 1 (T1), Type 2 (T2), etc, for easy reference, but as it happens T2, T4 and T6 are structurally similar (polyhedral head, tail structure and fibres for attaching to the surface of a bacterium), and this easily recognizable shape is now referred to as the T-Even phage.

Like all viruses, T-Even phages cannot reproduce extracellularly. They need a host cell in which to replicate their genetic material. An organism which reproduces like this is called an obligate parasite, and in the case of the T-Even phages, the process ends in the cell's death. The phage can attach to the surface of a bacterium using the proteins on its 'feet' (tail fibres), and inject its genetic material (either, but not both, DNA or RNA). This genetic material uses the host cell's ribosomes to replicate, and synthesise proteins for the capsid and tail of the phage. New phages are assembled within the cell - up to 200 - until the cellular membrane lyses (splits open). The newly made phages are now free to attack more cells. This is the Lytic cycle.¹

¹ Biology, Seventh Edition - Neil Campbell and Jane Reece