Modularity and diversity of target selectors in Tn7 transposons

To spread, transposons must integrate into target sites without disruption of essential genes while avoiding host defense systems. Tn7-like transposons employ multiple mechanisms for target-site selection, including protein-guided targeting and, in CRISPR-associated transposons (CASTs), RNA guided targeting. Combining phylogenomic and structural analyses, we conducted a broad survey of target selectors, revealing diverse mechanisms used by Tn7 to recognize target sites, including previously uncharacterized target-selector proteins found in newly discovered transposable elements (TEs). We experimentally characterized a CAST I-D system and a Tn6022-like transposon that uses TnsF, which contains an inactivated tyrosine recombinase domain, to target the comM gene. Additionally, we identified a nonTn7 transposon, Tsy, encoding a homolog of TnsF with an active tyrosine recombinase domain, which we show also inserts into comM. Our findings show that Tn7 transposons employ modular architecture and co-opt target selectors from various sources to optimize target selection and drive transposon spread.

Automated summary

In order to spread, transposons need to integrate into target sites without disrupting essential genes and avoid being detected by host defense systems. Tn7-like transposons use various mechanisms, such as protein-guided or RNA-guided targeting, to select target sites. Through phylogenomic and structural analyses, researchers discovered different target-selector proteins used by Tn7 to recognize target sites, including previously unknown ones found in newly discovered transposable elements (TEs). The study also experimentally characterized a CAST I-D system and a Tn6022-like transposon, uncovering the role of TnsF in targeting the comM gene, and identified a nonTn7 transposon, Tsy, that inserts into comM using a homolog of TnsF with an active tyrosine recombinase domain. These findings highlight the modular architecture of Tn7 transposons and their ability to adapt target selectors from various sources to optimize target selection and facilitate transposon spread.