Figure 1.

Integrons structure, acquisition and functions. Gene cassettes are sequentially inserted into an array by recombination between attI and the cassette associated-recombination sites, attC; Pc, an integron-carried promoter; and intI, a gene for the integron integrase. A single ORF (arrow) is expressed by the Pc promoter on gene cassettes (various genes are depcited with various colors). Pc is located between intI and attI in certain integrons. Cassettes have two ORFs, no ORF, or an ORF pointing in the opposite direction. IntI is transcribed in the same direction as the gene cassettes in certain genera.