Exciting genomic engineering possibilities exist for natural integration systems, called transposons, which have co-opted CRISPR/Cas systems. How insertions occur in a single orientation at a precise distance from the protospacer has been enigmatic. It has been mysterious how the transposase (TnsB) is recruited by the ATPase TnsC to the point of insertion marked by TniQ. We find orientation of the integration event is set by polar growth of a TnsC filament terminated at TniQ. TnsB dissociates TnsC filaments in a process driving the search for new TniQ-programed integration sites. Fixed TnsC structures found as hydrolysis intermediates suggest a spacing mechanism marking the precise point of TnsB-mediated insertion. This model suggests multiple avenues for engineering these systems.
https://science.sciencemag.org/content/early/2021/07/14/science.abi8976