Discovery and Tuning of RNA Editing Guides via High-Throughput Screening and Chemical Modification.

Adenosine deaminases acting on RNA (ADAR) catalyze the deamination of adenosine to inosine in double-stranded RNA. Because inosine is read as guanosine during translation, this process enables programmable A-to-G recoding at the transcript level. ADARs can be harnessed for therapeutic correction of pathogenic mutations through site-directed RNA editing with guide RNAs. To expand the design space of editing-enabling guides, we applied EMERGe, a high-throughput screening platform, to identify motifs targeting a premature termination codon in the MeCP2 transcript associated with Rett syndrome. This uncovered a guide RNA motif that supported efficient ADAR2-mediated editing in vitro, featuring a 5'-GUG-3' sequence predicted to form an asymmetric loop. To enable therapeutic application, structure-activity relationship studies and chemical optimization were performed, yielding a fully modified guide RNA with 2'-O-methyl, 2'-fluoro, and phosphorothioate linkages. This stabilized guide retained the activity of unmodified RNA and showed enhanced nuclease resistance. The optimized guide induces dose-dependent editing at two MECP2 loci in reporter assays in HEK293T cells, demonstrating that EMERGe-selected motifs can be rendered viable in cells through targeted chemical modification. These findings highlight the utility of EMERGe as a discovery platform and establish a pipeline for identifying and optimizing editing-enabling guide RNA features beyond traditional design rules.