by the integrase and at which gene cassettes may be inserted a promoter: Pc, which directs transcription of cassette-encoded genes Gene cassettes 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. 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. In more modern usage, an integron located on a bacterial chromosome is termed a sedentary chromosomal integron, and one associated with transposons or plasmids is called a mobile integron''. References Medical terms Further reading External links IntegronFinder - A tool to detect integrons in bacterial genomes INTEGRALL - The Integron Database Genetics Bacteriology Enzymes