Effective in vivo RNA base editing via engineered cytidine deaminase APOBECs fused with PUF proteins

Base editing stands at the forefront of genetic engineering, heralding precise genetic modi cations with broad implications. While CRISPR-based DNA and RNA base editing systems capitalize on sgRNA-guided speci city and diverse deaminase functionalities, the pursuit of ef cient C-to-U RNA editing has been hampered by the inherent constraints of cytidine deaminases. Here, we report an RNA base editing platform by re ning cytidine deaminases, termed pro- fessional APOBECs (ProAPOBECs), through systematic enhancements and AI- driven protein engineering. ProAPOBECs demonstrate unprecedented cata- lytic versatility, particularly fused with RNA-recognizing Pumilio and FBF (PUF) proteins. We demonstrate that in vivo RNA base editing of Pcsk9 using ProA- POBECs effectively lowers cholesterol levels in mice. Additionally, AAV- mediated RNA base editing with ProAPOBECs in the brain of an autism mouse model not only corrects point mutations in Mef2c mRNAs but also signi cantly alleviates disease-associated phenotypes. This work introduces a pioneering collection of RNA base editing instruments, emphasizing their therapeutic potential in combatting genetic disorders.