Natural Nucleoside Modifications in Guide RNAs Can Modulate the Activity of the CRISPR-Cas9 System .

At the present time, the clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein 9 (Cas9) system has been widely adopted as an efficient genomic editing tool. However, there are some actual problems such as the off-target effects, cytotoxicity, and immunogenicity. The incorporation of modifications into guide RNAs permits enhancing both the efficiency and the specificity of the CRISPR-Cas9 system. In this study, we demonstrate that the inclusion of -methyladenosine, 5-methylcytidine, and pseudouridine in trans-activating RNA (tracrRNA) or in single guide RNA (sgRNA) enables efficient gene editing . We found that the complexes of modified guide RNAs with Cas9 protein promoted cleavage of the target short/long duplexes and plasmid substrates. In addition, the modified monomers in guide RNAs allow increasing the specificity of CRISPR-Cas9 system and promote diminishing both the immunostimulating and the cytotoxic effects of sgRNAs.