Reining in Cas13a activity with N-terminal removable tags expands Cas13a based molecular sensing and enables precise gene interference

Activation of Cas13 is exclusively dependent on crRNA-target RNA hybridization according to the canonical mode of Cas13 action. Upon activation Cas13 can cleave both target RNA and any surrounding RNA. The latter has been well adopted by therapeutic gene interference and biosensor development. This work for the first time, rationale designs and validates a multi-component controlled activation system of Cas13 by N-terminus tagging. A composite SUMO tag comprised of His, Twinstrep, and Smt3 tags fully suppresses target dependent activation of Cas13a by interfering with crRNA docking. The suppression releases upon proteases mediated proteolytic cleavage. The modular composition of the composite tag can be altered to fulfill customized response to alternative proteases. The biosensor SUMO-Cas13a is able to resolve a broad concentration range of protease Ulp1 with a calculated LOD of 48.8pg/μL in aqueous buffer. Further, in accordance with this finding Cas13a was successfully programmed to exert target gene knock down preferentially in SUMO protease high cell types. In summary the discovered regulatory component not only fulfills Cas13a based protease detection for the first time, but also delivers a novel strategy for multi-component controlled activation of Cas13a toward temporal and spacial precision.