Figure 1. Schematic representation of class 1 (C1) integrons. In0 is the most basic integron that does not contain any gene cassettes. Different cassette arrays can be integrated in the variable region of the integron. Abbreviations: intI1, class 1 integrase gene; Pc and P2, gene cassette promoters; attI1, integron-associated recombination site; qacEΔ1, truncated version of a quaternary ammonium resistance gene; sulI, sulphonamide resistance gene; orf5, open reading frame; attC, recombination site of the gene cassette; GC, gene cassette; 5′-CS,5′ conserved segment of the integron; 3′-CS,3′ conserved segment of the integron.