Two prime editing guide RNAs (pegRNAs), deliver Cas9 enzymes to targeted regions of the genome. The enzymes nick opposite strands of the DNA at different points, at which point the pegRNA serves as a template for the desired gene insertion. This results in two single-stranded DNAs (ssDNA) that bind to each other due to their partially complementary sequence and, if they outcompete the original DNA, are integrated into the genome and completed by the host cell’s existing DNA repair machinery. Because two pegRNAs are used, GRAND editing can insert segments of up to 1,000 base pairs long—more than what one pegRNA could deliver alone.
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