A novel mechanistic framework for precise sequence replacement using reverse transcriptase and diverse CRISPR-Cas systems
CRISPR/Cas systems coupled with reverse transcriptase (RT), such as the recently described Prime editing, allow for site-specific replacement of DNA sequences. Despite widespread testing of Prime editing, it is currently only compatible with type II CRISPR/Cas proteins such as Streptococcus pyogenes and Staphylococcus aureus Cas9. Enabling RT compatibility with other CRISPR/Cas domains, such as type V enzymes with orthogonal protospacer adjacent motif specificities and smaller protein size would expand the range of edits that can be made in therapeutic and industrial applications. We achieve this with a novel mode of DNA editing at CRISPR-targeted sites that reverse transcribes the edit into the target strand DNA (e.g., the complement of the PAM-containing strand), rather than the non-target strand DNA, as in Prime editing. We term this technology RNA encoded DNA replacement of alleles with CRISPR (hereafter, REDRAW). We show that REDRAW extends the utility of RT-mediated editing beyond type II to include multiple type V CRISPR domains. REDRAW features a broad (8-10 bases) targeting window, at which all types of substitutions, insertions and deletions are possible. REDRAW combines the advantages of type V CRISPR domains with the extensive range of genetic variation enabled by RT-mediated, templated sequence replacement strategies.