Synergistic effect of split DNA activators of Cas12a with exon-unwinding and induced targeting effect

CRISPR-Cas12a, an RNA-guided nuclease, has been repurposed for genome editing and molecular diagnostics due to its capability of cis-cleavage on target DNA and trans-cleavage on non-target single-strand DNA (ssDNA). However, the mechanisms underlying the activation of trans-cleavage activity of Cas12a, particularly in the context of split DNA activators, remain poorly understood. We elucidate the synergistic effect of these activators and introduce the concepts of induced targeting effect and exon-unwinding to describe the phenomenon. We demonstrate that upon binding of split DNA activators adjacent to the Protospacer Adjacent Motif (PAM) to the Cas12a ribonucleoprotein (Cas12a-RNP), a ternary complex form that can capture and interact with distal split DNA activators to achieve synergistic effects. Notably, if the distal activator is double-strand DNA (dsDNA), the complex initiates exon-unwinding, facilitating the RNA-guide sequence's access. Our findings provide a mechanistic insight into action of Cas12a and propose a model that could significantly advance our understanding of its function.