Faculty Opinions recommendation of Integron cassette insertion: a recombination process involving a folded single strand substrate.
Fred Dyda · Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature · 2006
Integrons play a major role in the dissemination of antibiotic resistance genes among Gram-negative pathogens.Integron gene cassettes form circular intermediates carrying a recombination site, attC, and insert into an integron platform at a second site, attI, in a reaction catalyzed by an integron-specific integrase IntI.The IntI1 integron integrase preferentially binds to the 'bottom strand' of single-stranded attC.We have addressed the insertion mechanism in vivo using a recombination assay exploiting plasmid conjugation to exclusively deliver either the top or bottom strand of different integrase recombination substrates.Recombination of a single-stranded attC site with an attI site was 1000-fold higher for one strand than for the other.Conversely, following conjugative transfer of either attI strand, recombination with attC is highly unfavorable.These results and those obtained using mutations within a putative attC stem-and-loop strongly support a novel integron cassette insertion model in which the single bottom attC strand adopts a folded structure generating a double strand recombination site.Thus, recombination would insert a single strand cassette, which must be subsequently processed.