Genome-editing tools are central to generate experimental systems, test hypotheses and increasingly for clinical applications. A pair of recent Nature articles identified a programmable genome-editing tool in autonomous transposable elements known as insertion sequences (IS) by studying the mechanistic and structural properties of their interaction with target and donor DNA.

To further investigate the role of these ncRNAs in IS110 activity, Durrant et al. began by focusing on one member of the IS110 family, IS621. The authors used small RNA sequencing to confirm that ncRNAs were transcribed from an IS621 plasmid in Escherichia coli. Next, they demonstrated by affinity measurements that ncRNA transcribed from IS621 in vitro binds strongly to the IS621 recombinase. Further analyses showed notable sequence covariation between regions of the ncRNAs and both the target (the genomic insertion site) and donor (the IS621 plasmid) DNAs, indicating regions of the ncRNAs base-pair with target and donor DNA. In vitro reconstitution experiments that combined the transcribed ncRNA, purified IS621 recombinase, target and donor DNA showed that all four components were required to form the expected recombination product. This experiment also showed that the ncRNA–recombinase complex binds to both the donor and target DNA (but not non-complementary DNA), leading the authors to name these ‘bridge RNAs’.