Integron

An integron is a two component gene capture and dissemination system, initially discovered in relation to antibiotic resistance, and which is found in plasmids, chromosomes and transposons. The first component consists of a gene encoding a site specific recombinase along with a specific site for recombination, while the second component comprises fragments of DNA called gene cassettes which can be incorporated or shuffled.

An integron with a large number of cassettes may be called a super-integron, as in Vibrio cholerae chromosome 2. A cassette may encode genes for antibiotic resistance, although most genes in integrons are uncharacterized. An integron contains an integrase (int1) related to those of a phage, followed by an attI site for integration of cassettes and recognition of the integrase , and a promoter to drive expression. An integron may appear in a plasmid or on the chromosome. 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.

A functional integron "platform" requires:

• an integrase: intI, a tyrosine recombinase responsible for incorporation into the genome
• a proximal recombination site: attI, which acts as the locus for reincorporation to the genome. It combines with a attC site at the insertion site.

Further reading

• INTEGRALL The Integron Database
• Journal of Bacteriology, June 2002, p. 3017-3026, Vol. 184, No. 11 article Characterization of the Class 3 Integron and the Site-Specific Recombination System It Determines
• NCBI Antimicrob Agents Chemother. 1998 Dec;42(12):3053-8. article Class 1 integron-borne multiple-antibiotic resistance carried by IncFI and IncL/M plasmids in Salmonella enterica serotype typhimurium
• Nature Reviews Microbiology 4, 608-620. Mazel, D. Integrons: agents of bacterial evolution

Superintegrons is an incorrect term to call an integron platform associated with long cassette arrays. Most of the integron platforms that contain hundreds of gene cassettes such as in Vibrio cholerae are found as par of the bacterial chromosome. Therefore the integron nomeclature that depicts them should be as chromosomal integrons and not superintegrons and those that mobilise on plasmids or transposons and contain small numbers of gene cassettes or no gene cassettes as mobile integrons.

Sources

• Medical terms

Superintegrons, is an incorrect term used for an integron platform associated with long cassette arrays. Most integron platforms that contain hundreds of gene cassettes, such as in Vibrio cholerae, are found as part of the bacterial chromosome. Therefore, the integron nomeclature that depicts them should be named as chromosomal integrons and not superintegrons, and as for those that mobilise on plasmids or transposons and contain small numbers of gene cassettes or no gene cassettes,should be referred as mobile integrons.