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

Sources

• Medical terms