Integron

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Integrons are genetic units characterized by their ability to capture and incorporate gene cassettes by site-specific recombination.

Discovery

They were initially discovered in relation to antibiotic resistance.[1]

Structure

An integron is minimally composed of:[2][3]

  • a gene encoding for a site-specific recombinase: intI, belonging to the integrase family
  • a proximal recombination site: attI, which is recognized by the integrase[4] and at which gene cassettes may be inserted
  • a promoter: Pc, which directs transcription of cassette-encoded genes

Gene Cassettes

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Additionally, an integron will usually contain one or more gene cassettes that have been incorporated into it. The gene cassettes may encode genes for antibiotic resistance, although most genes in integrons are uncharacterized. An attC sequence (also called 59-be) is a repeat that flanks cassettes and enables cassettes to be integrated at the attI site, excised and undergo horizontal gene transfer.

Occurrence

Integrons may be found as part of mobile genetic elements such as plasmids and transposons. Integrons can also be found in chromosomes.

Terminology

The term super-integron was first applied in 1998 (but without definition) to the integron with a long cassette array on the small chromosome of Vibrio cholerae.[5][6] The term has since been used for integrons of various cassette array lengths or for integrons on bacterial chromosomes (versus, for example, plasmids). Use of "super-integron" is now discouraged since its meaning is unclear.[5]

References

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Further reading

External links

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  1. Integrons: agents of bacterial evolution (Mazel 2006), Nature Reviews Microbiology 4, 608-620 | doi:10.1038/nrmicro1462
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  3. Hall R, Collis C, Kim M, Partridge S, Recchia G, Stokes H (1999) Mobile gene cassettes and integrons in evolution. Ann. New York Acad. Sci. 870:68–80.
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