Escherichia virus T4

Escherichia virus T4 is a species of bacteriophage that infects Escherichia coli bacteria. The T4 phage is a member of the T-even bacteriophages, a group characterized by their unique structural properties and life cycle. It is a complex virus, notable for its large size, sophisticated infection mechanism, and the extensive genetic studies it has undergone. The study of T4 has significantly contributed to the fields of molecular biology and genetics, providing insights into virus-host interactions, DNA replication, and gene regulation.

Structure

The T4 phage has an icosahedral head structure, approximately 120 nm in diameter, which contains its DNA genome. The head is connected to a tail structure, around 113 nm in length, which ends in a baseplate with tail fibers. These tail fibers are crucial for the initial recognition and attachment of the phage to specific receptor sites on the E. coli cell surface. The T4 genome is made of double-stranded DNA and contains about 169 kbp, encoding around 300 genes.

Life Cycle

The life cycle of Escherichia virus T4 can be divided into several stages: attachment, penetration, biosynthesis, maturation, and release.

• Attachment: The T4 phage attaches to the host cell via its tail fibers binding to specific receptors on the E. coli surface.
• Penetration: After attachment, the phage contracts its tail sheath, injecting its DNA into the host cell.
• Biosynthesis: The phage DNA hijacks the host's cellular machinery to begin synthesizing phage components, shutting down the host's normal DNA, RNA, and protein synthesis.
• Maturation: Assembly of new phage particles begins once enough components have been synthesized.
• Release: Mature phages are released from the host cell by lysing the cell wall, typically resulting in the death of the host cell.

Genetics and Molecular Biology

The genetics of Escherichia virus T4 have been extensively studied, revealing complex regulatory mechanisms. The T4 genome contains genes that are expressed in a temporally controlled manner, with early, middle, and late genes. Early genes are involved in taking over the host cell's machinery and include enzymes for nucleotide metabolism. Middle and late genes are primarily involved in the synthesis of new phage components and assembly.

Applications and Significance

Escherichia virus T4 has been a valuable model organism in molecular biology and genetics. It has been used to study DNA replication and repair, transcription, and the regulation of gene expression. Additionally, T4's ability to specifically target and kill E. coli has led to its exploration as a tool in phage therapy, an alternative to antibiotics for treating bacterial infections.

See Also

• Bacteriophage
• Molecular biology
• Genetics
• Phage therapy