Figure 1

General structure of class 1 integrons. Cassettes are inserted in the variable region of integrons by a site-specific recombination mechanism. The attI1 and attC sites are shown by a vertical rectangle and oval, respectively, and promoters are denoted by Pint, Pc and P. Integrated cassettes are composed of a gene and an attC recombination site. Genes are as follows: intI1, integrase gene; qacEΔ1, antiseptic resistance gene; sul1, sulphonamide resistance gene; orf5, gene of unknown function.