The term co-option refers to the capacity of

intracellular parasite Intracellular parasites are microparasites that are capable of growing and reproducing inside the cells of a host. Types of parasites There are two main types of intracellular parasites: Facultative and Obligate. Facultative intracellular para ...

s to use host-cell

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

s to complete their vital cycle.

Virus A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsky's 1 ...

es use this mechanism, as their

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...

is small. It is also used in a different sense to refer to characters that have been exapted.

Flu virus

Because of its medical importance, the

influenza A '' A virus'' (''IAV'') causes influenza in birds and some mammals, and is the only species of the genus ''Alphainfluenzavirus'' of the virus family '' Orthomyxoviridae''. Strains of all subtypes of influenza A virus have been isolated from wi ...

virus has been characterized to a large extent, and is mentioned here as an example of co-option. Its

encodes only for 11 proteins, and it needs to use host-cell genes and proteins to carry out its

lytic cycle The lytic cycle ( ) is one of the two cycles of viral reproduction (referring to bacterial viruses or bacteriophages), the other being the lysogenic cycle. The lytic cycle results in the destruction of the infected cell and its membrane. Bacter ...

. In 2010, a study was realized to determine which host-cell factors are necessary for the entry and replication of Influenza A virus. Using

siRNA Small interfering RNA (siRNA), sometimes known as short interfering RNA or silencing RNA, is a class of double-stranded RNA at first non-coding RNA molecules, typically 20-24 (normally 21) base pairs in length, similar to miRNA, and operating wi ...

techniques, the effect of the disruption of more than 19,000 human genes on influenza life cycle was studied. That allowed identifying 295 host-cell genes needed for the virus to complete its lytic cycle, 23 of which are used during the entry steps, and the 219 remaining for the post-entry steps. Of all these genes implicated on the virus vital cycle, 168 might be targets for developing

antiviral drug Antiviral drugs are a class of medication used for treating viral infections. Most antivirals target specific viruses, while a broad-spectrum antiviral is effective against a wide range of viruses. Unlike most antibiotics, antiviral drugs do n ...

s for the treatment of

H1N1 In virology, influenza A virus subtype H1N1 (A/H1N1) is a subtype of influenza A virus. Major outbreaks of H1N1 strains in humans include the Spanish flu, the 1977 Russian flu pandemic and the 2009 swine flu pandemic. It is an orthomyxovirus ...

infection. It is important to emphasize that these targets are not virus proteins, but host-cell proteins.

References

{{DEFAULTSORT:Co-option (biology) Parasitism Virology