Enterobacteria phage T4 is a phage that infects E. coli bacteria. Its DNA is 169-170 kbp long; one of the longest DNAs in phages, and is held in an icosohedral head. T4 is also one of the largest phages, at approximately 90 nm wide and 200 nm long (most phages range from 25 to 200 nm in length). Its tail fibres allow attachment to a host cell, and the T4’s tail is hollow so that it can pass its nucleic acid to the cell it is infecting during attachment. T4 is only capable of undergoing a lytic lifecycle and not the lysogenic life cycle.

Lifecycle

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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 lifecycle is complete the host cell bursts open and ejects the newly built viruses into the environment, at which point the host cell is destroyed.

Unique features

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The T4 phage has some unique features, such as:

• Eukaryote-like introns
• High speed DNA copying mechanism, with only 1 error in 300 copies
• Special DNA repair mechanisms

Caudovirales