PubReading [138] - Improving CRISPR–Cas specificity with chemical modifications in single-guide RNAs - D. Ryan, D. Dellinger et al

<p><strong>CRISPR</strong> systems have emerged as transformative tools for altering genomes in living cells with un- precedented ease, inspiring keen interest in increasing their specificity for perfectly matched targets. We have developed a novel approach for improving specificity by incorporating chemical modifications in <strong>guide RNA</strong>s (gRNAs) at specific sites in their <strong>DNA recognition</strong> sequence (‘guide sequence’) and systematically evaluating their on-target and off-target activities in biochemical DNA cleavage assays and cell-based assays. Our results show that a chemical <strong>modification</strong> (2′-O-methyl-3′-phosphonoacetate, or ‘MP’) incorporated at select sites in the ribose- phosphate backbone of gRNAs can dramatically re- duce off-target cleavage activities while maintaining high on-target performance, as demonstrated in clinically relevant genes. These findings reveal a unique method for enhancing specificity by chemically modifying the guide sequence in gRNAs. Our approach introduces a versatile tool for augmenting the performance of CRISPR systems for research, industrial and therapeutic applications.</p><p><em>doi: 10.1093/nar/gkx1199 - 2018</em></p>