Conditional guide RNA through two intermediate hairpins for programmable CRISPR/Cas9 function: building regulatory connections between endogenous RNA expressions.

A variety of nanodevices developed for nucleic acid computation provide great opportunities to construct versatile synthetic circuits for manipulation of gene expressions. In our study, by employing a two-hairpin mediated nucleic acid strand displacement as a processing joint for conditional guide RNA, we aim to build artificial connections between naturally occurring RNA expressions through programmable CRISPR/Cas9 function. This two-hairpin joint possesses a sequence-switching machinery, in which a random trigger strand can be processed to release an unconstrained sequence-independent strand and consequently activate the self-inhibitory guide RNA for conditional gene regulation. This intermediate processor was characterized by the fluorescence reporter system and applied for regulation of the CRISPR/Cas9 binding activity. Using plasmids to generate this sequence-switching machinery in situ, we achieved the autonomous genetic regulation of endogenous RNA expressions controlled by other unrelated endogenous RNAs in both E. coli and human cells. Unlike previously reported strand-displacement genetic circuits, this advanced nucleic acid nanomachine provides a novel approach that can establish regulatory connections between naturally occurring endogenous RNAs. In addition to CRISPR systems, we anticipate this two-hairpin machine can serve as a general processing joint for wide applications in the development of other RNA-based genetic circuits.