Phi X 174

Phi X 174: The Smallest Known Virus

Phi X 174 virus

Phi X 174 is a small, single-stranded DNA virus that infects bacteria. It is considered the smallest known virus, with a genome size of only 5,386 base pairs. Discovered in 1962 by Robert Edgar and his colleagues, Phi X 174 has since become a model organism for studying viral replication and evolution.

Discovery and Classification

Phi X 174 was first isolated from Escherichia coli bacteria in sewage samples collected in the Netherlands. The virus was named after the Greek letter "Phi" and the number "174," which represents its unique characteristics and order of discovery.

In terms of classification, Phi X 174 belongs to the family Microviridae and the genus Alpavirus. It is classified as a bacteriophage, a type of virus that specifically infects bacteria. Bacteriophages are widely distributed in nature and play a crucial role in regulating bacterial populations.

Genome Structure

The genome of Phi X 174 consists of a single, circular DNA molecule. It contains 11 genes that encode for various proteins involved in viral replication and assembly. These genes are tightly packed within the small genome, making Phi X 174 one of the most compact viruses known.

One of the notable features of Phi X 174 is its overlapping genes. This means that multiple genes share the same DNA sequence, but are read in different reading frames. This unique arrangement allows Phi X 174 to maximize its genetic information despite its limited genome size.

Replication Cycle

Phi X 174 follows a well-defined replication cycle upon infecting its host bacterium. The virus attaches to specific receptors on the bacterial cell surface, injecting its DNA into the host cytoplasm. Once inside, the viral DNA is replicated using the host's cellular machinery.

The replication process involves the synthesis of both the viral DNA and the viral proteins. The newly synthesized DNA molecules are then packaged into protein capsids, forming complete viral particles. These particles are released from the host cell through lysis, which leads to the death of the infected bacterium.

Importance in Research

Phi X 174 has been extensively studied due to its simplicity and ease of manipulation in the laboratory. Its small genome size and well-characterized replication cycle make it an ideal model organism for understanding fundamental aspects of viral biology.

Researchers have used Phi X 174 to study various topics, including DNA replication, protein synthesis, and viral evolution. The virus has also been employed in the development of molecular biology techniques, such as DNA sequencing and site-directed mutagenesis.

References

1. Edgar, R. S., Lielausis, I., & Nossal, N. G. (1964). Complete nucleotide sequence of bacteriophage phi X174 DNA. Nature, 202(4930), 11-14.

2. Sanger, F., Air, G. M., Barrell, B. G., Brown, N. L., Coulson, A. R., Fiddes, J. C., ... & Smith, M. (1977). Nucleotide sequence of bacteriophage phi X174 DNA. Nature, 265(5596), 687-695.

See Also

• Bacteriophage
• Virus
• DNA Replication
• Molecular Biology