New CRISPR tool opens up more of the genome for editing
The genome editing system CRISPR has become a hugely important tool in medical research, and could ultimately have a significant impact in fields such as agriculture, bioenergy, and food security. The targeting system can travel to different points on the genome, guided by a short sequence of RNA, where a DNA-cutting enzyme known as Cas9 then makes the desired edits. However, despite the gene-editing tool’s considerable success, CRISPR-Cas9 remains limited in the number of locations it can visit on the genome. That is because CRISPR needs a specific sequence flanking the target location on the genome, known as a protospacer adjacent motif, or PAM, to allow it to recognize the site. For example, the most widely used Cas9 enzyme, Streptococcus pyogenes Cas9 (SpCas9), requires two G nucleotides as its PAM sequence, significantly restricting the number of locations it can target, to around 9.9 percent of sites on the genome. As yet, there are only a...