Figure 2.

Acquisition of gene cassettes into the integron’s platform. New gene cassettes are acquired through the recombination of the attl site of integrons and the attC site of the circular gene. The new incoming gene is inserted at the proximal position of the integrase gene next to the embedded promoter. The repeated acquisition leads to the expansion of the cassette array, but the cassettes can be excised in the reverse of acquisition either by att1-attl or attC-attc recombination.