Gene cassette transcription in a large integron-associated array

We demonstrated that the majority of the cassette-associated genes in the subject array were expressed. We further showed that cassette expression was conditional and that the conditionality varied across the array. We finally showed that this expression was mediated by a diversity of cassette-borne promoters within the array capable of responding to environmental stressors.Widespread expression within large gene cassette arrays could provide an adaptive advantage to the host in proportion to the size of the array. Our findings explained the existence and maintenance of large cassette arrays within many prokaryotes. Further, we suggested that repeated rearrangement of cassettes containing genes and/or promoters within large arrays could result in the assembly of operon-like groups of co-expressed cassettes within an array. These findings add to our understanding of the adaptive repertoire of the integron/gene cassette system in prokaryotes and consequently, the evolutionary impact of this system.Integrons are genetic elements capable of mobilising and rearranging genes packaged as mobile gene cassettes in a site-specific manner [1]. In concert with other mechanisms capable of mobilising DNA between cells, the integron/gene cassette system contributes to the overall process of lateral gene transfer (LGT). LGT is a major contributor to genetic diversity amongst prokaryotes [2] and hence a significant force in prokaryote evolution. The ability of the integron/gene cassette system in particular, to influence the evolution of prokaryote strains is graphically shown in the rapid dissemination of antibiotic resistance genes both geographically and amongst different prokaryotes [3]. However, cassette-associated genes are not limited to the provision of antibiotic resistance phenotypes, with a plethora of novel ORFs (open reading frames or putative genes) present in the gene cassette metagenome [4]. While the majority of the ORFs contained within gene cassettes have no analo