Figure 3

Model of cassette integration mediated by integron integrases. The site-specific recombination reaction is carried out between the folded bottom strand of an attC site and the attI site of an integron. (a) Two integrase monomers bind each DNA molecule. (b) Attacking monomer on each DNA molecule cuts one of the two strands. (c) Strand exchange of cut strands. (d) Ligation of exchanged strands forms a Holliday junction. (e) This intermediate structure could be resolved by DNA replication, generating three products, one of which contains the inserted cassette. The attacking monomers are shown by gray circles and the non-attacking monomers are shown by white circles. Y: catalytic tyrosine residues. Adapted from [28].