T7 phage

T7 phage is a species of bacteriophage that infects Escherichia coli bacteria. It is a member of the Podoviridae family, characterized by its short, non-contractile tail. T7 phage is widely studied in molecular biology and genetics due to its relatively simple structure and the specificity of its infection cycle. This bacteriophage has been instrumental in understanding gene expression, virus-host interactions, and the mechanics of DNA replication.

Structure

T7 phage has an icosahedral head structure, approximately 60 nm in diameter, which contains its linear, double-stranded DNA genome. The genome is about 40 kilobases in length and encodes approximately 55 genes. The short, non-contractile tail of the T7 phage is distinctive, featuring six tail fibers that are crucial for the recognition and attachment to the host cell's surface.

Life Cycle

The life cycle of T7 phage begins with the attachment of the phage to the outer membrane of the E. coli cell, mediated by the tail fibers recognizing specific receptor sites. Following attachment, the phage injects its DNA into the host cell. The T7 phage DNA then hijacks the host's cellular machinery to begin synthesizing phage proteins and replicating its DNA.

The early genes are expressed first, encoding proteins that modify the host's RNA polymerase to preferentially transcribe the phage's DNA. Middle and late genes are expressed subsequently, directing the assembly of new phage particles and the lysis of the host cell to release them. The entire cycle from infection to lysis can occur in as little as 30 minutes under optimal conditions, resulting in the release of 100 to 200 new phage particles.

Genetic Studies

T7 phage has been a valuable model organism in genetic studies. Its relatively small and well-characterized genome makes it an ideal system for studying gene expression and regulation. Researchers have used T7 phage to develop novel genetic engineering techniques, including the T7 expression system, which is widely used for the overexpression of recombinant proteins in E. coli.

Applications

Beyond its contributions to basic science, T7 phage has applications in biotechnology and medicine. Phage display technology, which involves expressing foreign peptides or proteins on the surface of phage particles, has been used for vaccine development, drug discovery, and the identification of protein interactions. Additionally, due to the growing problem of antibiotic resistance, bacteriophages like T7 are being explored as potential alternatives to traditional antibiotics for treating bacterial infections.

See Also

• Bacteriophage
• Escherichia coli
• Virology
• Genetic engineering
• Phage therapy