Small Cas13 proteins enable compact RNA base editors

CRISPR-Cas13 systems have been developed for precise RNA editing, an attractive therapeutic strategy when temporary changes are desirable or DNA editing is not possible. We identified and characterized an ultra-small family of Cas13b, Cas13b-t, and showed it mediates mammalian transcript knockdown. By functionalizing Cas13b-t with adenosine and cytosine deaminase domains, we engineered compact variants of REPAIR and RESCUE RNA editors, which may be more amenable for in vivo use.