The bacterial SOS response promotes the expression of the transposase encoded by IS CR mobile genetic elements

Insertion sequences (IS) are widely involved in bacterial genomic plasticity by disrupting, adding, moving genomic sequences, or by activating or extinguishing gene expression. A specific family of IS, IS CR (for insertion sequence of Common Region), is thought to be involved in the dissemination of antibiotic resistance genes (ARG). While some IS CR members are commonly found in bacteria isolated in clinical settings and can contribute to downstream ARG expression, the mechanisms regulating the IS CR -encoded transposases expression have remained uncharacterized. Here, we investigated the expression of the transposase gene of ISCR1, ISCR2 and ISCR8, and its regulation in Escherichia coli . Using in silico analyses and in vitro experiments, we showed that expression levels were extremely low, as observed for most IS transposases. We further demonstrated the direct role of DNA damages and the key SOS response repressor, LexA, in controlling the activity of transposase promoter. These results provide evidence that the mobility of at least some IS CR elements may be promoted upon bacterial exposure to antibiotics inducing the SOS response.