E-Mail Researchers from Skoltech and their colleagues from Russia and the US have described two new, compact Cas9 nucleases, the cutting components of CRISPR-Cas systems, that will potentially expand the Cas9 toolbox for genome editing. One of the two nucleases has been shown to work in human cells and thus can have biomedical applications. The paper was published in the journal Nucleic Acids Research. CRISPR-Cas, the genome editing technology borrowed from bacteria, relies on Cas nucleases; these enzymes, when guided by CRISPR RNAs, can degrade target genetic sequences -- they are the blades in the Nobel Prize-worthy 'genetic scissors.' In research applications, the most popular Cas9 nuclease is the Streptococcus pyogenes one, Type II-A SpCas9. It is efficient and relatively simple, as one large protein both binds to crRNA and cleaves DNA; it also requires a short PAM -- a string of nucleotides bookending the target site that the enzyme uses to locate and 'read' it.